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Boundary layer transition from laminar to turbulence is of vital importance to the design of hypersonic vehicles. With continuous expansion of flight speed and altitude domains, the high-temperature gas effects in hypersonic high-enthalpy boundary layers invalidate the calorically perfect gas assumption. They can thus largely influence the flow transition process. Relevant research is multi-interdisciplinary and multi-physics coupling. In recent years, the hypersonic high-enthalpy boundary layer transition has received increasing interest worldwide owing to rapid development of vehicle design. Recent progress is reviewed in this article. Firstly, commonly used high-temperature gas models are introduced, especially the thermochemical non-equilibrium models. Then, the prevailing computational methods for high-enthalpy flows, including the shock-capturing, shock-fitting and boundary layer equation methods are introduced. The progress in experimental techniques for high-enthalpy wind tunnels and flight tests are also summarized. Afterward, the influences of high-temperature effects on the receptivity, modal growth, transient growth and nonlinear interactions in the transition process are reviewed. Here some phenomena has received wide interests that the third mode and the supersonic mode appear at relatively large growth rates in the streamwise instability. Finally, the progress is summarized, and future researches are briefly prospected.
2022, 54(11): 2937-2957.   doi: 10.6052/0459-1879-22-184
In this paper we investigate the evolution dynamics of side-by-side droplets after being impacted by a planar shock by using a three-dimensional conservative sharp interface method. Our research mainly focuses on the development of wave structures after the shock impact and the asymmetric interface evolution of single droplet induced by the coupling between the side-by-side droplets. Firstly, we analyze the development of the wave system including those inside and outside the channel between the side-by-side droplets. We find that at the early stage of impact, the intersection of reflected shock waves accounts for the formation of new reflected shock waves and Mach rods. This is quite different from the curved wave front formed by the reflected shock wave on the other side of the droplet transversely opposite to the channel. The difference of the flow field on the two sides of the droplet is responsible for the asymmetric interface evolution of the droplet in the middle stage of the droplet-shock interaction. Secondly, we investigate the interface morphology and its evolution in the middle stage of shock impact, especially when the incident shock wave moves to the downstream of and is far away from the droplets, and report the occurrence of new flow phenomena at the downstream outlet of the channel, such as interface coalescence caused by airflow expansion and subsequent interface fragmentation owing to airflow blockage. Finally, the effect of the gap between the side-by-side droplets on the droplet interaction is studied. We find that the gap size has a significant effect on the occurrence of pressure peaks in the channel. Specifically, a smaller gap not only brings higher pressure peak, but also makes the peak appear at an earlier time.
2022, 54(11): 2958-2969.   doi: 10.6052/0459-1879-22-358
Based on the control of the near wake flow of a wavy cylinder by steady blowing and suction to enhance the vibration of the cylinder, the effects of the forward blowing and backward suction and the forward and backward suction control modes on the lift and drag characteristics, time-average pressure coefficient, circulation, turbulent kinetic energy and flow field mechanism of a wavy cylinder under different blowing and suction conditions at subcritical Reynolds number (Re = 3000) were numerically studied by large eddy simulation. It is found that the fluctuating lift coefficient of wavy cylinder under the control of forward blowing and backward suction and forward and backward suction is significantly increased under different conditions of blowing and suction momentum coefficient, and the maximum increase is as high as 636% and 391% respectively compared with that of uncontrolled cylinder and wavy cylinder. This may be mainly attributed to the shorter recirculation area of wavy cylinder under the control of blowing and suction, the concentration of high-intensity vortices towards the rear of blunt body, and the shorter vortex formation length, The "riblike vortex" formed by the interaction of spanwise vortex and streamwise vortex becomes larger and longer, and the normalized circulation near the wake increases significantly, resulting in the increase of fluctuating lift coefficient, which may lead to stronger vibration of the cylinder; At the same time, both control methods change the pressure distribution on the surface of the wavy cylinder. Because the front end tends to be streamlined due to the blowing at the front stagnation point of the wavy cylinder, the high-pressure area of the wavy cylinder decreases under different blowing and suction momentum coefficients, but the low-pressure area increases due to the suction at the rear stagnation point, while the high-pressure area of the wavy cylinder is basically unchanged and the low-pressure area increases under different blowing and suction momentum coefficients. The research results can provide basic theoretical support for improving the efficiency of distributed wind energy capture structure in low wind speed areas.
2022, 54(11): 2970-2983.   doi: 10.6052/0459-1879-22-212
Atmospheric density is a fundamental parameter for vehicle designing and flight controlling. In recent years, many researchers have discovered that atmospheric densities in the upper mesosphere and lower thermosphere predicted by the empirical model, such as USSA-76 and NRLMSISE-00, are larger than the measured values. On the other hand, vehicle designing is tending to be more detailed, and engineers hope that the empirical models provide densities under variable latitudes, day-night times and seasons. Based on that, the present work analyzesdependences of near-space atmospheric density on latitude, solar local time and date, by using satellite observed data. Emphasizes are put on density fluctuation patterns and amplitudes. The fluctuation patterns caused by latitude and date vary with altitude, and the amplitudes are largest at 78 km and locally smallest at about 22 km and 92 km. The fluctuation amplitude caused by the solar local time increases monotonically with altitude. Based on the temporal-spatialfluctuationlaw, we proposed the temporal-spatial fluctuation modelfor the near-space atmospheric density, which describes the density fluctuations with latitude, local time and date. The present model describes the temporal-spatial fluctuations better than the existed empirical models at variable altitudes. The confidence coefficient of the present model is much better than NRLMSISE-00 under the same error band. The modeling method in this work is reasonable, and the obtained model could be used in near-space vehicle designing.
2022, 54(11): 2984-2993.   doi: 10.6052/0459-1879-22-231
Based on the Brinkman-extended Darcy model and the local thermal equilibrium model, the fluid flow and heat transfer characteristics in the multilayered-parallel fractured porous channel are studied. The analytical solutions of velocity field, temperature field in each region of multilayered-parallel fractured porous channel, friction coefficient and Nusselt number are obtained. The effects of the fracture number, Darcy number, hollow ratio and the ratio of effective thermal conductivity on heat transfer characteristics are analyzed. The results show that when Darcy number is small, the Darcy velocity in the porous media which does not change with the porous height increases with the increase of the number of fracture layers, and is not affected by the porous layer position in multilayer porous channel with certain number of fractures. Increasing the number of fracture layers weakens the influence of hollow ratio on pressure drop and increases the fluid pressure drop in the channel, but the increase degree gradually decreases. The increase of the ratio of effective thermal conductivity or decrease of the hollow ratio leads to a stepwise temperature distribution in the multilayered fractured porous channel, while the temperature distribution curves in the multilayered fractured channel tend to be consistent when the thermal conductivity ratio is small or the hollow ratio is large. Furthermore, when the ratio of thermal conductivity is small, the heat transfer effect in multilayered fractured porous channel is better than that in single fractured porous channel at any hollow ratio. However, when the ratio of thermal conductivity is large, there is a critical hollow ratio, which makes the heat transfer effect in the channels with different numbers of fracture layers be the same, and increasing the number of fractured layers has little influence on the heat transfer effect in multilayered fractured porous channel.
2022, 54(11): 2994-3009.   doi: 10.6052/0459-1879-22-285
The traditional mapped weighted essentially non-oscillatory (WENO) schemes commonly suffer from the drawback of low-efficiency, since they usually require the mapping processes resulting in extra computational costs. The goal of the present work is to improve the efficiency of the mapped WENO schemes. By designing a set of approximate constant mapping function which is devised using an approximation of the standard signum function, a novel mapped WENO scheme is proposed. The new mapping function is devised to meet the overall criteria for a proper mapping function required in the design of the WENO-PM6 scheme. The WENO-PM6 scheme was presented to overcome the potential loss of accuracy of the well-validated WENO-M scheme in previously published literature. The new proposed mapped WENO scheme is denoted as WENO-ACM. It maintains almost all advantages of the WENO-PM6 scheme, such as low dissipations and high resolutions. However, it decreases the number of mathematical operations remarkably in every mapping process leading to a significant improvement of efficiency. Theoretical analysis indicates that the new scheme can attain the optimal convergence rate of accuracy regardless of critical points. The investigation of approximate dispersion relation (ADR) shows that the spectral properties of the new scheme are significantly improved. A variety of benchmark-test problems, including accuracy tests, standard shock-tube problem, Mach 3 shock-entropy wave interaction, Woodward-Colella interacting blast waves, 2D Riemann problem, double Mach reflection, forward-facing step problem, Rayleigh-Taylor instability and Kelvin-Helmholtz instability are conducted. Compared to the well-established WENO-JS, WENO-M, WENO-PM6 schemes comprehensively, the present scheme exhibits significantly improved high efficiency, very high resolution and sharp discontinuity capturing. Most importantly, the extra computational cost of WENO-ACM compared to WENO-JS is much lower than those of WENO-M and WENO-PM6. Specifically, WENO-ACM can reduce the extra computational cost compared to WENO-JS more than 80% and 90% against WENO-M and WENO-PM6, respectively.
2022, 54(11): 3010-3031.   doi: 10.6052/0459-1879-22-247
Vortex identification is a very important problem of fluid and flow, in order to find a reasonable method of vortex identification in the wake of marine propeller, this paper studies the theory of six kinds of vortex recognition technology combined with practice, in which analytic solutions of both Burgers vortex and Lamb-Oseen vortex are also used for necessary explanation. The advantages and disadvantages of various vortex identification methods are discussed in detail at the angle of theory and application. The local low-pressure criterion is intuitive, but it is obviously insufficient after considering viscous and unsteady effects. The path line or streamline criterion obviously cannot satisfy Galileo invariance, which will cause confusion in vortex identification. The magnitude of vorticity criterion needs to specify its threshold value, which has certain uncertainty, and can also incorrectly identify vortex sheets that are not vortices. The complex eigenvalue of the velocity gradient tensor will also have an unrecognized region. The second invariant criterion of the velocity gradient tensor and the second eigenvalue criterion of the symmetric tensor can better identify the vortex core, and these two criteria are sometimes equivalent. The numerical simulation of propeller wake is implemented on the open source software OpenFOAM platform. The large eddy model is modeled by a local dynamic equation, which is better than the dynamic Smagorinsky model to a certain extent. The results of numerical experiment show that, for the vortex identification in the marine propeller wake, the second invariant criterion of the velocity gradient tensor is consistent with the second eigenvalue criterion of the symmetric tensor. However, the local minimum pressure criterion, streamline or path line criterion, vorticity magnitude criterion and complex eigenvalue criterion of velocity gradient tensor have some defects, which are not suitable for vortex identification in the wake of marine propeller.
2022, 54(11): 3032-3041.   doi: 10.6052/0459-1879-22-339
The experimental measurement of the flow field around the circular cylinder near the wall is carried out by using the Particle Image Velocimetry. The characteristics of the flow regime under different Reynolds numbers (${Re} = {1500} \sim {5540}$) together with three different gap ratios (${G \mathord{\left/ {\vphantom {G D}} \right. } D}{ \;= 0}{.5}$, ${G \mathord{\left/ {\vphantom {G D}} \right. } D}{\; = 1}{.0}$, ${G \mathord{\left/ {\vphantom {G D}} \right. } D}{ \;= 1}{.5}$) are studied. The experiment results shows that for the case of ${G \mathord{\left/ {\vphantom {G D}} \right. } D}{ \;= 0}{.5}$, with the increasing of Reynolds number, the recirculation zone behind the cylinder is gradually symmetrical about the centerline of the cylinder while its size is decreasing, and the size of the separation bubble on the wall also decreases gradually. The experiment reveals that the cylindrical wake and the gap flow perform differently while the Reynolds numbers ${{Re} _t}$ between ${Re} = {3000} \sim {3200}$. When the Reynolds number is smaller than ${{Re} _t}$, a small separation bubble will form on the front wall of the cylinder, which hinders the flow of upstream fluid through the gap and reduces the intensity of the gap flow, and then deviates from the wall. At ${Re} { \;= 1500}$, the vortex shedding frequency increases with the decrease of the gap ratio. And with the decrease of gap ratio, the vortex shedding frequency increases first and then decreases in a small range (${0}{.185} \leqslant St \leqslant {0}{.227}$) for ${Re} \geqslant {3000}$. The Reynolds number has a significant influence on the flow characteristics, especially for the case of small gap ratios. At ${G \mathord{\left/ {\vphantom {G D}} \right. } D}{ \;= 0}{.5}$, the secondary vortex deviates from the wall and moves upward to the position close to the upper wake vortex, and the vortex merging process appears between the upper wake vortex and the secondary vortex for the ${Re} { \;= 1500}$. As the Reynolds number increases to ${Re} { \;= 5540}$, the secondary vortex does not merge with the upper wake vortex, and the secondary vortex directly interacts with the lower wake vortex. At ${G \mathord{\left/ {\vphantom {G D}} \right. } D}{ \;= 1}{.0}$ and ${G \mathord{\left/ {\vphantom {G D}} \right. } D}{ \;= 1}{.5}$, the energy carried by the secondary vortex is decreasing gradually with the increasing of Reynolds number.
2022, 54(11): 3042-3057.   doi: 10.6052/0459-1879-22-403
For numerical simulation of high-speed flows, it requires that small-scale structures are resolved with high-fidelity, and discontinuities are stably captured without spurious oscillation. These two aspects put forward almost contradictory requirements for numerical schemes. The widely used high-order schemes can satisfy the two demands required above to some extent. However, they all have advantages and disadvantages compared to each other and no one can be considered perfect. For example, high-order schemes are prone to generating numerical oscillations near discontinuities when a small-scale problem is discretized, such as the Reynolds-stress model. To solve this deficiency, a simple, effective and robust modification is introduced to the seventh-order weight compact nonlinear scheme (WCNS) by making use of the descaling function to formulate a scale-invariant WCNS scheme. The descaling function is devised using an average of the function values and introduced into the nonlinear weights of the WCNS7-JS/Z/D schemes to eliminate the scale dependency. The design idea of the scale-invariant WCNS scheme is to make weights independent of the scale factor and the sensitivity parameter. In addition, the shock-capturing ability of the new scheme performs well even for small-scale problems. The new schemes can achieve an essentially non-oscillatory approximation of a discontinuous function (ENO-property), a scale-invariant property with an arbitrary scale of a function (Si-property), and an optimal order of accuracy with smooth function regardless of the critical point (Cp-property). We derive the seventh-order D-type weights. The one-dimensional linear advection equation is solved to verify that WCNS schemes can achieve the optimal (seventh) order of accuracy. We test a series of one- and two-dimensional numerical experiments governed by Euler equations to demonstrate that the scale-invariant WCNS schemes perform well in the shock-capturing ability. Overall, the scale-invariant WCNS schemes provide a new method for improving WCNS schemes and solving nonlinear problems.
2023, 55(1): 1-18.   doi: 10.6052/0459-1879-22-399
In the past few decades, although traditional computational methods such as finite element have been successfully used in many scientific and engineering fields, they still face several challenging problems such as expensive computational cost, low computational efficiency, and difficulty in mesh generation in the numerical simulation of wave propagation under infinite domain, large-scale-ratio structures, engineering inverse problems and moving boundary problems. This paper introduces a class of collocation discretization techniques based on physical-informed kernel function to efficiently solve the above-mentioned problems. The key issue in the physical-informed kernel function collocation methods is to construct the related basis functions, which includes the physical information of the considered differential governing equation. Based on these physical-informed kernel functions, these methods do not need/only need a few collocation nodes to discretize the considered differential governing equations, which may effectively improve the computational efficiency. In this paper, several typical physical-informed kernel functions that satisfy common-used homogeneous differential equations, such as the fundamental solutions, the harmonic functions, the radial Trefftz functions and the T-complete functions and so on, are firstly introduced. After that, the ways to construct the physical-informed kernel functions for nonhomogeneous differential equations, inhomogeneous differential equations, unsteady-state differential equations and implicit differential equations are introduced in turn. Then according to the characteristics of the considered problems, the global collocation scheme or the localized collocation scheme is selected to establish the corresponding physical-informed kernel function collocation method. Finally, four typical examples are given to verify the effectiveness of the physical-informed kernel function collocation methods proposed in this paper.
2022, 54(12): 3352-3365.   doi: 10.6052/0459-1879-22-485
CO2 microbubble is a promising enhanced oil recovery and carbon sequestration method. In this paper, based on microbubbles porous media generation method, a self-designed microbubble generator featuring the porous ceramic membrane was developed. The morphology and dissolution characteristics of CO2 microbubbles at different initial CO2 concentrations were experimentally investigated. The results showed that the CO2 microbubbles prepared at 10 MPa were distributed in the range of 10 ~ 70 μm with an average bubble diameter of 34.43 μm. At 15 MPa, CO2 microbubbles with smaller diameter were generated, with an average bubble radius of 25.03 μm. However, under high salinity condition, microbubbles with average diameter of 277.17 μm were produced. The brine salinity decreased microbubbles stability, which leading to bigger bubble. In a word, the microbubbles diameter was highly affected by the pressure in microbubbles porous medium generation method. Then, the static and dynamic dissolution kinetics of microbubbles in the porous media were investigated by microfluidics. The results of dissolution experiments showed that microbubbles had excellent dissolution efficiency. When contacting with formation water, microbubbles would rapidly dissolve and the undissolved microbubbles were still migrating the porous media in the form of bubbles. CO2 microbubbles could form a migration mode with carbonated water in the front and microbubbles in the rear, after microbubble were injected into the reservoir. For the first time, the enhanced oil recovery mechanisms of CO2 microbubbles were studied under high-temperature high-pressure conditions, which mainly include: ①Microbubbles carry residual oil on the pore wall during migration; ②Microbubbles carry residual oil droplets out of the pores with dead ends through dissolution and oil swelling; ③Break the capillary force balance of residual oil droplets and promote the flow of oil droplets; ④Block the high permeability channel to improve the sweep efficiency. This paper provides valuable guidance for CO2 microbubble to enhanced oil recovery and carbon sequestration.
2023, 55(1): 1-11.   doi: 10.6052/0459-1879-22-507
The ultra-low friction impact ground pressure of deep coal rock is essentially a time-varying process in which a large amount of coal rock mass is instable and sliding along the coal-rock interface, during which the friction and friction coefficient of the coal-rock interface change with time, and at the same time, the energy conversion characteristics of releasing energy from the impact kinetic energy of the coal-rock interfacial with the frictional force of the coal-rock interface. In order to quantitatively describe the energy conversion law of coal rock interface, the dimensional analysis method is introduced, and the elastic coefficient, damping coefficient and pending coefficient of coal rock are experimentally determined, and the expression of the friction coefficient of deep coal rock interface is given. Taking Shenyang Hongyang Three Mines as the research object, through the combination of experimental research and engineering practice, a new index of impact kinetic energy conversion rate is defined, the reliability of the built model is verified, and the law of coal-rock interface friction work to coal-rock impact kinetic energy conversion is quantitatively described. The results show that the interfacial friction coefficient of deep coal rocks decreases linearly with the increase of the amplitude of the impact load, and increases linearly with the increase of the frequency of the impact load. When the impact load amplitude is 5000 N and the impact load frequency is 500 Hz, the ultra-low friction effect occurs when the friction force of deep coal rock interface decreases by 97% and the reduction rate is 38.9 kN/ms ~ 41.38 kN/ms. For the first time, the ultra-low friction effect is quantitatively described in terms of friction reduction amplitude and reduction rate. Combined with the experimental and engineering actual analysis, it is found that the average experimental result of the energy consumption ratio is 0.441, and the calculation result of the "11.11" impact ground pressure of Hongyang Three Mines is 0.488, which is relatively close, which further proves the rationality of the proposed model.
2023, 55(2): 1-13.   doi: 10.6052/0459-1879-22-467
In order to achieve the drag reduction effect, the experimental scheme of zero-mass jet active control turbulent boundary layer is designed independently in the paper. Dual piezoelectric (PZT) oscillators as the active control actuators are symmetrically distributed embedded along the spanwise direction of the flat plate in turbulent boundary layer. The experimental investigation is carried out by synchronous (syn) and asynchronous (asyn) vibration active control mode to achieve drag reduction with the periodic vibration of dual PZT oscillators in a wind tunnel. It realizes the periodic interference and modulation to the multi-scale coherent structure in turbulent boundary layer. Furthermore, it reduces the skin friction and realizes drag reduction effect in all controlled cases.The consequence shows that the maximum drag reduction rate of 18.54% is obtained at 100 V, 160 Hz asynchronous vibration case.The multi-scale wavelet analysis of streamwise velocity shows that the energy of the small-scale coherent structure increases while the large-scale coherent structure decreases in all controlled conditions.Meanwhile, it adjusts the energy distribution of the large-scale and small-scale coherent structures in near-wall regions of turbulent boundary layer .The drag reduction effect of the asynchronous controlled case is better than the synchronous controlled case at the same voltage and frequency of vibration. When the vibration frequency of the PZT oscillators is 160 Hz, the PDF curves of the wavelet coefficient show the fluctuation characteristics and the tails of the PDF curve widen significantly. The pulsations of near-wall regions become more ordered and regular and the turbulence weakens intermittently after control in turbulent boundary layer.The results of the conditional phase averaging of small-scale coherent structure show that the periodic perturbations of the PZT oscillators enhance the turbulence intensity of the small-scale coherent structures. Furthermore, drag reduction effect is also achieved by breaking the large-scale coherent structure into the small-scale coherent structure. As the streamwise position is far away from the PZT oscillators, the modulation effect of the coherent structure in turbulent boundary layer gradually weakens.
2023, 55(1): 1-10.   doi: 10.6052/0459-1879-22-248
The WENO-S scheme is a class of weighted essentially non-oscillatory schemes suitable for numerical simulations of problems with discontinuities. The smoothness indicator of this kind of scheme is constant for single-frequency waves, which makes this kind of scheme have exactly the same approximate dispersion relationship with its linear base scheme, and thus has an excellent ability to simulate small-scale waves. Time efficiency is crucial for numerical methods. For a WENO-S scheme, the formula of the smoothness indicator on each sub-stencil has the same formula except for different subscripts. Then some smoothness indicators are the same when calculating adjacent numerical fluxes of linear convection equations. So, a method is proposed to remove redundant computations of smoothness indicators. The premise of this approach is that the quantity used for reconstruction or interpolation on a grid line can be represented as a sequence. According to this requirement, the feasibility and application requirements for several different physical problems are analyzed. The seventh-order WENO-S scheme is employed to illustrate the advantages of the WENO-S schemes, including good properties near extreme points, good stability near discontinuities, and outstanding spectral properties. Then the method of eliminating the computation of the redundant smoothness indicators is introduced. In numerical computation, all smoothness indicators in a grid line are calculated and stored in advance. With this approach, the count of the smoothness indicator calculation is about 1/4 of the original one for the seventh-order WENO-S scheme when there are many grid points. Numerical examples include one-dimensional advection, spherical wave propagation, two-dimensional rotation, small disturbance propagation, and one- and two- dimensional inviscid flow problems. The numerical results show that this scheme can capture a variety of flow structures well and have good time efficiency. Furthermore, the proposed method reduces the computational time by about 20%.
2023, 55(1): 1-15.   doi: 10.6052/0459-1879-22-371
2022, 54(12): 1-2.   doi: 10.6052/0459-1879-22-557
A ship always encounters waves and may move with six degrees of freedom in the naval architecture and ocean engineering. The ship can be regarded as a rigid body simply when the motion amplitude is small. However, when the wave gets severe, the ship's motion amplitude get large and the ship hull may deforms a lot. In this situation, ship's elasticity may effects the pressure on the hull and the ship response motion, which cannot be ignored. Therefore, it is of great significance to simulate the motion of an elastic ship in waves and to study the influence of the hull elasticity, which can improve the ship performance and the navigation safety. MPS (Moving Particle Semi-Implicit) method is a mesh free particle method based on Lagrangian representation. This method has its unique advantages in simulating problems with large deformation characteristics of free surfaces. As a traditional structural solution method, Finite Element Method (FEM) has been widely used and has been proved with good stability, accuracy and robustness. In this paper, the advantages of MPS method and FEM method are combined and the in-house fluid-structure interaction solver MPSFEM-SJTU is used to simulate the motions of rigid and elastic hulls in regular waves. The impact of hull elasticity on the hull motion response and the pressure on the hull is analyzed. Firstly, the effect of regular wave length on the motion response of hull is studied by simulating the motion of a rigid hull in regular waves with different wavelengths. Then the motions of rigid and elastic hull in regular waves are simulated respectively. The results show that the motion amplitude of rigid hull, both pitch and heave, are greater than those of the elastic hull. and the pressure near the midship of elastic hull is greater than that of rigid hull. For the pressure distribution on elastic and hull surface, the pressure at the bottom near the midship is greater than that on the rigid hull due to the bending of the elastic ship.
2022, 54(12): 1-14.   doi: 10.6052/0459-1879-22-468
In order to accurately describe the characteristics of each stage of rock creep behavior under the combined action of acid environment and true triaxial stress, based on the chemical kinetic theory of water-rock interaction, a chemical damage factor considering pH and time is defined. The elastic body, nonlinear Kelvin body, linear Kelvin body, and visco-elastic-plastic body (Mogi-Coulomb) are connected in series, and the actual situation under the action of true triaxial stress is considered at the same time, a damage-creep constitutive model considering the coupling of rock acid corrosion and true triaxial stress is established. The parameters of the deduced model are identified and verified with the existing experimental research results. The yield surface equation of rock under true triaxial stress is obtained by data fitting, and the influence of intermediate principal stress on the creep model is discussed. The results show that the derived constitutive model can well reflect creep properties of the rock under acid corrosion The true triaxial creep characteristics under the action have certain rationality and practicability
Aiming at the problems that there is a certain difference between the muscle fiber microstructure model and the image observed under the microscope, the microscopic component biomechanical model cannot effectively capture the mechanical behavior of skeletal muscle during shear deformation, and the high calculation cost of multi-scale numerical models of skeletal muscle. In this thesis, the mechanical properties of skeletal muscle are studied from the perspectives of experiment, multiscale modeling and simulation. Curved-edge Voronoi polygons are proposed as the cross-section of muscle fibers, and the corresponding representative volume element (RVE) is established at the microscale. A new biomechanical model (MMA model) is proposed, and the MMA model is used as the biomechanical model of muscle fibers and connective tissue. Combine the experimental results of skeletal muscle, the RVE models, the biomechanical models of muscle fibers and connective tissue to establish a multiscale numerical model of skeletal muscle. According to the experimental results, the parameters of the biomechanical model are determined, the multiscale homogenization method are used to realize the connection between the microscale and the macro-scale, and the macroscopic mechanical behavior of skeletal muscle is finally obtained.
Transition from laminar to turbulent flow of the hypersonic boundary layer can increase the wall friction coefficient and heat conduction coefficient by 3-5 times, which has a significant influence on flight performance and safety of hypersonic vehicles. Wavy roughness is a possible passive control method to delay hypersonic boundary layer transition, and is thus of engineering significance. In this paper we investigate the effort of finite-length wavy roughnesses with different locations and heights on the stability of a Mach 6.5 flat-plate boundary layer using direct numerical simulation and linear stability theory(LST). DNS is employed to obtain the laminar base flow, and to study the linear evolution of fixed-frequency disturbances parametrically introduced upstream by blowing and suction. The effects of the relative position of the fast/slow mode synchronization point and the wavy roughness are revealed. It is found that when the wavy roughness is placed upstream of a disturbance’s synchronization point, the disturbance is damped compared to the smooth surface case; when the disturbance’s synchronization point is within or slightly downstream of the wavy roughness, the disturbance is generally enhanced. The effects of heights of wavy roughnesses are also considered. For the wavy roughness with small heights compared to the boundary layer thickness, the effect of wavy roughness is positively correlated with the height of the wavy roughness, while the effect is weakened by the higher wavy roughness. Linear stability theory can predict well the effects of wavy roughness on high-frequency disturbances, but exhibits large discrepancies with DNS in predicting the behaviors of moderate and low-frequency disturbances. This indicates that the receptivity process and the strong non-parallel effect in the vicinity of the wavy roughness neglected by LST should play an important role.
Single crystal Ni-based alloys possess excellent properties such as high temperature resistance, high strength and high toughness. Thses mechanical properties are affected by secondary orientation and cooling holes induced during complex manufacturing processes. The current research mainly focuses on the deformation mechanism and mechanical response of plates with one hole. While, the plate with multiple holes is often used in engineering. At present, it is urgent to clarify the deformation mechanism of the plate with multiple holes, the secondary orientation effect, and the strain gradient effect caused by cooling holes. In this paper, a nonlocal crystal plasticity constitutive model based on the dislocation mechanism is used to numerically simulate the uniaxial tensile deformation behavior of the Ni-based single crystal plate with cooling holes. A dislocation flux term is derived based on the relationship between the plastic slip gradient and geometrically necessary dislocations, enabling this crystal plasticity model to effectively describe the strain gradient effect. In order to comprehensively reveal the secondary orientation effect of Ni-based alloys with cooling holes, this paper systematically studies the uniaxial tensile deformation behavior of sheets with [100] and [110] orientations (two secondary orientations). The influence of the number of holes on the plastic behavior of the plate with two secondary orientations is investigated. By analyzing the variation of the resolved stress on slip systems, activation of the dominant slip systems and the evolution of geometrically necessary dislocation density during the deformation of Ni-based alloy plates, the effects of plastic slip and its distribution on the strength of Ni-based alloy plates with different secondary orientations are discussed. The results show that the tensile strength of [110] plate is lower than that of [100] plate. Furthermore, the plastic deformation process of the five-hole plate is more complicated than that of the one-hole plate and is easier to be affected by secondary orientation. Finally, the location of the slip gradient is mainly located near the cooling hole and the plastic slip zone. The research results can provide theory basis for the design and service of Ni-based alloys in engineering.
Periydnamics (PD) is a new nonlocal method reformulated from solid mechanics. It adopts the integral form of governing equation and is naturally suitable to model fragments and cracks under extreme events, thus widely applied in the field of national defense security. However, the nonlocality in PD introduces the dispersion effect and imposes adverse effect on wave propagation, which will greatly restrict its capability in capturing solid behaviors, especially the fractures. For this purpose, we employ the spectral analysis method to study the dispersion behavior of PD system comprehensively. It is found that compared to the low frequencies, the dispersion relation of high frequency components shows an oscillation trend and zero-energy modes, leading to more serious dispersion problems. The dispersion behavior of high frequencies changes with the wave propagation direction and shows 45° symmetry in the spatial wave propagation. As the PD system itself is non-dissipative, the adverse effect of the dispersion problem can not be suppressed. As a result, the simulation accuracy may be greatly influenced. To introduce the numerical dissipation for dispersion effect suppression, the governing equation of viscosity introduction is proposed as a minimum variation of conventional PD. Both the typical deformation in solids and the selective suppression on high frequencies are considered then the corresponding viscous force state is constructed. Finally, a numerical study is conducted to model the shock waves under extreme events and investigate the influence of wave discontinuity. It is indicated that the wave discontinuity aggravates the dispersion problem and shows Gibbs instability in the wave propagation. These can be effectively suppressed by the viscous force state, which verifies the proposed method. This provides an important reference to reproduce the correct wave propagation process and obtain the reasonable solid behavior in PD, thus helps to support and guide the research of national defense security field.
The expansion stern is an important factor affecting the flatting trajectory and its stability of a trans-media vehicle during high speed water entry and turning flat process. In this paper, based on the fluid volume multiphase flow model and dynamic mesh technology, the coupling calculation method of multiphase flow field and trajectory of the trans-media supercavitating vehicle entering water at high speed is established. The accuracy and applicability of the numerical calculation method are verified by the experiments. Through the numerical simulation study on the high speed water entry and turning flat process of the trans-media vehicle, the influence of the expansion stern on the cavity development morphology, hydrodynamic characteristics and trajectory characteristics of the vehicle during the water entry and turning flat process is obtained, and the influence of the cone angle of expansion sterns on the flatting trajectory during high speed water entry is analyzed. The results show that when the vehicle without the expansion stern entering water and turning flat under the different preset rudder angles, the angle of attack increases continuously, eventually leading to the divergence of the flatting trajectory. After the vehicle with the expansion stern entering water, the recovery moment is formed when the expansion stern is wetted, and the stable flatting trajectory is obtained. The vehicles with different expansion stern cone angles (1.5°, 6°, 8°) have formed three different kinds of trajectory characteristics: stable planing, single-sided tail-slapping and double-sided tail-slapping, and all of them can achieve stable flatting trajectory. The principle of stable planing trajectory is the dynamic balance under the coupling effect of the preset rudder angle and expansion stern planing. This trajectory has the smallest comprehensive drag coefficient, the highest flatting efficiency and the smallest dynamic load, which is an ideal flatting trajectory form for the trans-media vehicle during high speed water entry.
Rotating blade is an essential part of aero-engine. It serves in harsh conditions. Its failure is often caused by excessive vibration. To design the blade properly and to ensure the reliability and safety, the vibration characteristics of the blade need to be revealed. The blade is simplified as a cantilever rotating pipe with double cooling channels based on the Euler-Bernoulli beam theory. The influences of channel axis offset on fluid kinetic energy are considered in the present study. The motion governing equation of the blade is established including the bi-gyroscopic effects with the combination of Lagrange principle and assumed mode method. The method of order reduction and dimension expansion is applied to solve the eigenvalue of the system. The influences of the fluid velocity ratio, rotating speed, slenderness et al. on the first three order eigenvalue curves are studied. The present model degenerates into a simply supported pipe conveying fluid with a single channel to compare with the results reported in literature. The correctness of the present modeling method is verified, partly. The velocity ratio of two channels has great influence on the first three order critical flow velocity values. For a given value of the cross-section area of the cooling passage, the critical flow velocity of the twin-channel model is higher than the single-channel model. A circling phenomenon is introduced to on the second and the third eigenvalue curves by the gyroscopic effect due to the rotating motion. The second and the third eigenvalue curves travel through the imaginary axis several times. With the increase of the slenderness ratio, the system’s dynamic behaviors are similar to the non-rotating cantilever pipe. Moreover, due to the gyroscopic effect, the modal response of the lateral displacement presents a traveling wave property. And the damping factor has different enhancement or weakening effects on the first three modes under different parameter conditions.
In the fields of aerospace, ships, oil pipelines and nuclear power, there will be cracks inevitably in structure or component part when running for a long time under extreme conditions. Therefore, it is necessary to explore the features of the stress-strain fields near the crack tip, to study the quasi-static fracture behavior of cracked structures. In this paper, the stress distributions near the tip of mode-I cracked specimens under plane strain and plane stress conditions are studied for power-law hardening material. Based on the energy density equivalence and dimensional analysis, the analytical equation of equivalent stress of representative volume element (RVE) with the median energy density of a finite-dimensions specimen is proposed, and it is defined as the stress factor. Furthermore, for Compact tension (CT) and Single edge bend (SEB) finite size specimens under plane strain and plane stress conditions, the stress factor is used as a characteristic variable, and a special trigonometric function is assumed to characterize Butterfly-Wings type or Scallop type contour lines of the equivalent stress near the mode-I crack tip, and then a semi-analytical model for compact tension specimens and single edge bend specimens under plane strain and plane stress and fully plastic conditions is proposed to describe the stress fields near the crack tip. As shown in comparing results given by finite element analysis to those predicted by the model for stress fields near the crack tip of the two cracked specimens, all agree well with each other. The semi-analytical model of stress field near the crack tip proposed in this paper is simple in form and accurate in result. It can be directly used to predict the stress distribution near the tip of mode-I crack, which is convenient for fracture safety evaluation and theoretical development.
2016, 48(4): 756-766.   doi: 10.6052/0459-1879-16-159

2017, 49(1): 3-21.   doi: 10.6052/0459-1879-16-348

2017, 49(1): 22-30.   doi: 10.6052/0459-1879-16-345

2019, 51(3): 656-689.   doi: 10.6052/0459-1879-18-381

2016, 48(4): 767-783.   doi: 10.6052/0459-1879-16-161

2017, 49(3): 550-564.   doi: 10.6052/0459-1879-17-064

2017, 49(2): 239-256.   doi: 10.6052/0459-1879-16-255

1978年，Barton提出的节理粗糙度系数（joint roughness coefficient，JRC）被国际岩石力学学会作为评估节理粗糙度的标准方法.然而该方法存在人为估值的主观性缺陷.就此，国内外学者围绕岩体结构面粗糙度定量化表征开展了大量的研究工作.首先，从二维节理轮廓线到三维岩体结构面，系统地阐述了其粗糙度定量化表征方法研究进展，并总结了各方法参数与JRC的关系；评价了各表征参数的本质特性及其适用性；指出了各方法参数获取过程中存在的问题，主要有：采样间隔的影响，三角形单元划分的影响，如何确定综合参数法中各参数的权重；针对这些问题，给出了笔者的一些想法、建议.与此同时，对结构面粗糙度表征的两个热点问题，即各向异性和尺寸效应的研究也进行了详细总结分析.最后，笔者认为：（1）分形维数因是描述自然界复杂几何体的一种简洁有力的工具，其仍是结构面粗糙度定量描述的有效方法；（2）3D打印技术的应用，有望在开展结构面各向异性、尺寸效应研究方面取得突破性进展.
2019, 51(1): 1-13.   doi: 10.6052/0459-1879-18-054

2016, 48(4): 741-753.   doi: 10.6052/0459-1879-16-069

2016, 48(3): 519-535.   doi: 10.6052/0459-1879-15-436

2012, 44(2): 269-277.   doi: 10.6052/0459-1879-2012-2-20120210
Abstract PDF(42)
Abstract:
In order to predict the cavitating flow characteristics in cryogenic fluids more exactly, a revised cavitation model considering the thermal effect with modified the evaporation and condensation source terms is established, which is based on Kubota cavitation model. The computations for cavitating flows in liquid nitrogen are conducted around an axisymmetric ogive by employing Kubota cavitation model and the revised cavitation model, respectively. The computational results are compared with the experimental data to evaluate the revised cavitation model. It is found that for the results of the revised cavitation model due to considering the thermal effects, the evaporation becomes smaller and the condensation becomes larger, the cavity length is shorter and the cavity interface becomes more porous compared with the results of original Kubota model. The results of the revised cavitation model are more accordant with the experimental data, and it dictates that the revised cavitation model can describe the process of mass transport more accurately in the cavitation process in cryogenic fluids and it is applicable for computations of cavitating flows in cryogenic fluids flow.
2012, 44(2): 252-258.   doi: 10.6052/0459-1879-2012-2-20120208
Abstract PDF(21)
Abstract:
This study focuses on the velocity-annular-effect (VAE) of compressible oscillatory flow inside parallel plate channel. By analyzing the mechanism of VAE, we conclude that VAE, which inevitably occurs in viscous oscillatory pipe flow, is most visible at the phase when the centerline velocity reaches zero. In order to quantitatively evaluate the VAE, coefficient of velocity annular effect (CVAE) was proposed as an index parameter, based on the slope of velocity profile when the centerline velocity reaches zero. Numerical computations with the index parameter CVAE were conducted to analyze the impacts of dimensionless parameters, i.e., Valensi number Va and maximum Reynolds number Remax, on the VAE of oscillatory flow inside parallel plate channel.

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