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

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RRB JE ME CBT 2 Previous Paper 2: Held on 31 Aug 2019
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  1. Hyper-sonic flow 
  2. Sonic flow
  3. Super-sonic flow 
  4. Sub-sonic flow

Answer (Detailed Solution Below)

Option 4 : Sub-sonic flow
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Explanation:

Mach number

Mach number is defined as the ratio of inertia force to elastic force.

M=InertiaforceElasticforce=ρAV2KA=V2Kρ=VKρ=VC{Kρ=C=Velocityofsound}

M=Velocityofbodymovinginfluidvelocityofsoundinfluid

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 < 0.8

Sub-sonic flow

0.8 < M <1.3

Trans-sonic

M = 1

Sonic flow

1.3 < M < 5

Super-sonic flow

M > 5

Hypersonic flow

26 June 1

Other important dimensionless numbers are described in the table below

Reynold’s number

Re=inertiaforceviscousforce=ρVLμ

Froude Number

Fr=inertiaforcegravitationforce=VLg

Euler number

Eu=inertiaforcepressureforce=VP/ρ

Weber Number

We=inertiaforcesurfacetension=Vσ/ρL

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