# Why is critical Mach number of a sphere higher than a cylinder ?

Why is critical Mach number of a sphere higher than a cylinder ?

Asked on 13th January 2022 in

Critical Mach number is the free stream Mach number, such that local Mach number on the surface of the body is sonic.

The flow over a cylinder is a two dimensional flow. When there is a flow over a cylinder, the flow moves upwards and downwards.

The flow over a cylinder is a three dimensional flow. Therefore when there is a flow over a cylinder, it moves upward, downward and also in sideways, left and right.

Therefore, flow over a cylinder has a greater speed than the flow over a sphere. So, to achieve a sonic velocity on the sphere, freestream Mach number is higher than cylinder.

Therefore, critical Mach number of a sphere is higher than cylinder.