The origin of hysteresis may be relate to shear layer.The evolvement of counterflow and coflow shear layer present a difference behave, and may play a common role in main flow de-attachment.

• 其起因与剪切层有关，逆流剪切层和同向流剪切层的演化过程显著不同，并且可能两者对附体的脱离起了共同的作用。