Correct Answer : Thin
Explanation : Shock layer is defined as the distance between the surface body and the shock wave. For hypersonic flow, this distance is very less thus making the shock layer thin. The shock waves usually lies very close to the surface.
Correct Answer : Curved
Explanation : When a space shuttle having a blunt nose enter the earth’s atmosphere, it is at the hypersonic speed. In this case the shock wave produced is very thin which is a characteristic of hypersonic flow but is slightly detached from the nose at some distance ‘d’. The nose region has a highly curves shock wave present.
Correct Answer : Very high
Explanation : At the nose region of the slender body, the shock wave is considered to be a normal shock. The entropy change across a strong shock wave is high. Thus the entropy gradient in the nose region is extremely high because of strong normal shock.
Correct Answer : M > 5
Explaination : Flow with Mach number less than 1 is known as subsonic flow. Mach number greater than 1 is considered to be supersonic flow with sonic flow at Mach = 1. After Mach greater than 5, the flow properties change drastically and is known as hypersonic flow.
Correct Answer : True
Explanation : In case of hypersonic flow, the shock layer is very thin and the shock lies close to the surface of the body. This often leads to shock waves merging with the viscous boundary layer which is present at the surface.
Correct Answer : Loss of kinetic energy due to viscous effect
Explanation : When a very high velocity flow is over a body, the hypersonic flow has large amounts of kinetic energy. This is often dissipated and converted in the form of internal energy die to viscous effects within the boundary layer. This effect is known as the viscous effect.
Correct Answer : Increases
Explanation : Due to viscous dissipation, kinetic energy of the gas gets converted to the internal energy leading to rise in temperature inside the boundary layer. With increase in temperature, the viscosity coefficient also increases.
Correct Answer : Communication blackout
Explanation : At certain altitude and Mach number in hypersonic flow, the vehicles are unable to communicate by transmitting or receiving radio waves. This is due to the high temperature flow causing ionization of the chemically reactive flow which produces free electrons that absorb these radio waves. This is known as ‘communication blackout’.
Correct Answer : Ablative surface
Explanation : The re – entry vehicles at hypersonic speed undergo viscous dissipation. This leads to rise in temperature within the boundary layer leading to excitation of the molecules causing dissociation or ionization. The surface of these vehicles are usually coated with ablative surfaces because of its high melting point and inert nature.
Correct Answer : Interaction between inviscid flow and boundary layer
Explanation : The interaction between the outer inviscid flow and the boundary layer in hypersonic flow is known as viscous interaction. It played an essential role in surface pressure distribution in turn affecting drag, lift, moments, etc. over the object.
Correct Answer : Hypersonic
Explanation : For flows above Mach number 5 i.e. hypersonic flow, it is seen that the aerodynamic quantities such as coefficient of pressure, coefficient of life and wave drag become independent of the Mach number. This aspect was even described by Newton while formulating his Newtonian theory which states the coefficient of pressure is independent of Mach number at hypersonic speed.
Correct Answer : V.n = 0
Explaination : While non dimensionalising the governing equations for steady inviscid flow, the boundary condition applied is that the flow of tangent to the surface. This means that if V is the velocity vector and n is the unit normal vector at the surface, then for the flow to be tangent, V.n = 0.
Correct Answer : False
Explanation : The coefficient of drag over both conical cylinder and sphere becomes independent after a certain higher Mach number. This is known as Mach number independence. Although, this Mach number independence for sphere is achieve at a lower Mach number compared to the conical slender because for slender bodies, the Mach number independence occurs at a lower Mach number.
Correct Answer : Length of the body is same
Explanation : Two or more flows are considered to be geometrically similar when the flow over the bodies remains identical. This happens when the shape of the bodies is identical and the variation in non – dimensional parameters remain same for the flows.
Correct Answer : K = 0.5 to infinity
Explaination : Hypersonic similarity condition does not hold true for all values of K. For bodies which are very slender such as the cone having half angle of 3 degrees, the similarity stays valid only when the value of K ranges from 0.5 to infinity.
Explanation : While deriving for hypersonic similarity using the governing equations for hypersonic flow, there is no assumption made for rotational or irrotational flow. Thus, when the graph is plotted for both rotational and irrotational flow for different values of freestream velocity and slenderness ratio, both the graphs are same.
K
γ
Correct Answer : Hypersonic similarity parameter K and γ
Correct Answer : Product of Mach number and slenderness ratio
Explaination : The product of Mach number and slenderness ratio along with gamma are the two parameters which appear in the non – dimensional equations. For a body that has same shape but have different scale ratio, if these parameters are same, the flow over them at hypersonic regime remain same. This is the physical meaning of the hypersonic similarity parameter.
Correct Answer : Hypersonic flow over slender bodies
Explanation : Hypersonic similarity parameter K is an important governing parameter in order to study the hypersonic flow i.e. flow with Mach number greater than 5 over slender bodies. It is given by the product of free stream Mach number and flow deflection angle.
