When Mach number is less than unity, the flow is called-

Explanation

Explanation: Mach number Mach number is defined as the ratio of inertia force to elastic force. For the compressible fluid flow, Mach number is an important dimensionless parameter. On the basis of the Mach number, the flow is defined. Mach Number Type of flow M 5 Hypersonic flow Important Points Other important dimensionless numbers are described in the table below M = ​ = ​ Elastic force Inertia force ​ = ​ KA ρAV 2 ​ = ​ ​ ρ K V 2 ​ = ​ ​ ρ K V ​ ​ = C = V elocity of sound C V { ​ ρ K } M = ​ velocity of sound in fluid V elocity of body moving in fluid Reynold’s number Froude Number Euler number Weber Number