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Correct option is (b) False

Easiest 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.

The correct answer is (a) K = 0.5 to infinity

The BEST I can explain: 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.

The correct choice is (a) Hypersonic similarity parameter K and γ

Easy explanation: For the flow over a wedge having slenderness ratio τ has formation of OBLIQUE shock WAVES. The relation is given by:

\(\frac {C_p}{τ^{2}}\) = F(K,γ)

According to this, \(\frac {C_p}{τ^{2}}\) is a function of only GAMMA and the hypersonic similarity parameter.

Right option is (c) Length of the body is same

The explanation is: 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.

The correct option is (c) M∞T, \(\frac {α}{τ}\), γ

To explain: The lift coefficient over the body at hypersonic FLOW is obtained by integrating the pressure coefficient over the surface.

cl = \(\frac {1}{l} \int _0^{l}\)(Cpl – CPU)dx

Where, Cpl – Cpu are coefficient of pressure over the upper and lower surface

l is the length of body

The above equation in terms of X is

cl = \(\int _0^{1}\)(Cpl – Cpu)dx

Diving this equation with the square of slenderness ratio, we get

\(\frac {c_l}{τ^{2}} = \int _0^{1}\)(Cpl – Cpu)dx = f(M∞T, \(\frac {α}{τ}\), γ)

THUS, coefficient of lift is a function of M∞T, \(\frac {α}{τ}\) and γ.

The CORRECT choice is (b) Interaction between inviscid flow and boundary layer

To explain: 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.

Right choice is (c) Ablative surface

The BEST 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.

Right choice is (b) False

The EXPLANATION: When there is no FLUID transfer taking place between the surface, then in order to non dimensionalising the governing EQUATIONS, we use the boundary condition V.n = 0. But, when there is transfer of fluid in or out of the surface then normal velocity vT has to be incorporated thus altering the boundary condition as V.n = vT.

Correct answer is (b) False

The 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 CHOICE is (a) V.n = 0

For explanation: 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 is (a) Thin

Best 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.

The correct answer is (b) Product of Mach number and slenderness ratio

The best explanation: 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.

The correct ANSWER is (a) Communication blackout

The EXPLANATION is: 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’.

Right answer is (b) HYPERSONIC flow over slender bodies

Easiest 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.

The correct option is (b) 11.925 × 10^4 Pa

Easy EXPLANATION: Given, P1 = 2.65 × 10^4 Pa, M1 = 4, β = 30°

The NORMAL COMPONENT of the Mach number upstream of the shockwave is given by:

MN1 = M1sinβ = 4sin⁡(30) = 2

Using the normal shock table, for Mn1 = 2 we get the relation between the pressure upstream and DOWNSTREAM

\(\frac {P_2}{P_1}\) = 4.5

Since P1 = 2.65 × 10^4, we get P2 = 4.5 × 2.65 × 10^4 = 11.925 × 10^4 Pa.

Correct CHOICE is (a) 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.

The correct choice is (a) True

The best I can explain: The pressure inside the boundary layer remains constant (in the normal DIRECTION), but the TEMPERATURE increases due to viscous dissipation. Thus, from equation of state, there is a decrease in density making it IMPORTANT to have a larger boundary layer thickness to pass the MASS flow through the boundary layer. Due to this reason, the hypersonic boundary layer thickness grows MUCH more rapidly compared to other flow regimes.

Right option is (a) LOSS of kinetic energy due to viscous effect

Easiest 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.

The correct answer is (a) True

To elaborate: 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.

Right choice is (d) HYPERSONIC

To elaborate: 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 choice is (b) 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.

Right choice is (b) False

Explanation: For two bodies at HYPERSONIC regime at very small angle of attack, apart from product of Mach number and slenderness ratio M∞τ and the VALUE of gamma γ, there is ONE more condition to be met to have SIMILAR dynamic flow. That condition is that the ratio of angle of attack to slenderness ratio (α/τ) should be same.

Right answer is (a) 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.