Numerical simulations of low-speed turbulent flowsaround a slender body are conducted to explore the effect of a minutenose geometrical disturbance on the formation and development of flowasymmetry. The result shows that the asymmetric flows observed inexperiment are simulated successfully by the introduction of a smallbump placed near the body apex. The asymmetric vortex structure growsgradually along the symmetry axis of the slender body, and thedistribution of sectional side force takes the sinusoid character ofvariation. Disturbance energy presents exponential spatial growth fromthe tip until it reaches the saturation. Disturbance scale influencesthe size and the distribution of flow asymmetry. The flow asymmetryshows a single periodicity when the circumferential position of thesingle disturbance changes. Numerical results show that the asymmetricvortex flow originates from the spatial instability of the forebodywake induced by a small disturbance.