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This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.

1.

Why can’t build an ideal supersonic diffuser with no total pressure losses?(a) Presence of shock waves(b) Varying cross – sectional area(c) Varying throat area(d) Choked flowThe question was asked in a job interview.I would like to ask this question from Quasi-One-Dimensional Flow Diffusers topic in section Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Right CHOICE is (a) Presence of shock waves

Best explanation: DUE to the presence of oblique shock waves on the convergent portion, the ideal supersonic diffuser is far from achievable. This CONTRIBUTES to the breaking of the isentropic flow characteristics according to which the entropy in the diffuser is constant. In fact, the flow in REALITY is viscous and there is an increase in entropy near the boundary LAYER.

2.

What is the diffuser efficiency of a normal shock diffuser?(a) 1(b) 0(c) Inifinty(d) \(\frac {1}{2}\)The question was asked in my homework.I want to ask this question from Quasi-One-Dimensional Flow Diffusers in division Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Right answer is (a) 1

The best explanation: The diffuser efficiency compares the actual pressure ratio of a diffuser \(\frac {p_{d_{0}}}{p_0}\) and the TOTAL pressure ratio ACROSS a normal shock \(\frac {p_{0_{2}}}{p_{01}}\) . The formula is given by:

ηD = \(\frac {(\frac {p_{d_0}}{p_0})_{actual}}{(\frac {p_{0_2}}{p_{01}} )_{normal \, shock \, at \, M_e}}\)

The numerator will be equal to the denominator for a normal shock diffuser, hence the efficiency is one. For subsonic FLOW, the siffuder’s performance is LOWER resulting in efficiency which is LESS than unity. And for the hypersonic flow the efficiency is greater than unity since it has a better shock recovery.

3.

How is flow deaccelerated In the diffuser?(a) Isentropic compression(b) Isentropic expansion(c) Adiabatic compression(d) Adiabatic expansionI have been asked this question in examination.Question is from Quasi-One-Dimensional Flow Diffusers in chapter Quasi-One-Dimensional Flow of Aerodynamics

Answer»

The correct choice is (a) ISENTROPIC compression

The explanation is: The diffuser’s function is to slow down the INCOMING high speed flow to a lower subsonic flow. The aim is to reduce the velocity with small loss in total PRESSURE. The IDEAL diffuser does this task with the HELP of isentropic compression so that there is no pressure loss.

4.

In the area – Mach relation A < A^* or A ≥ A^*.(a) True(b) FalseThe question was posed to me in a national level competition.The doubt is from Nozzles in chapter Quasi-One-Dimensional Flow of Aerodynamics

Answer»

The correct answer is (b) False

Explanation: In case of AREA – Mach relation, the value of A can never be less than A^* for an isentropic flow because this corresponds to the throat area where Mach number is EQUAL to 1 and has a local minimum area because dA = 0.

5.

Which equation is obtained when Mach number is equated to zero in area-velocity relation?(a) Momentum equation(b) Continuity equation(c) Energy equation(d) Bernoulli’s equationI got this question in semester exam.My doubt stems from Area-Velocity Relation in chapter Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Right option is (b) Continuity equation

For explanation: The area-velocity relation is given by:

\(\frac {dA}{A}\)=(M^2-1)\(\frac {du}{U}\)

In the above equation if we substitute M=0 we get,

\(\frac {dA}{A}=-\frac {du}{u}\)

On INTEGRATING this equation we get:

Au=constant

This is the continuity equation for INCOMPRESSIBLE flow in a DUCT

6.

Sonic flow exists at the throat of an equilibrium chemically reacting nozzle flow?(a) True(b) FalseThe question was asked in a national level competition.My question comes from Area-Velocity Relation in portion Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Correct option is (a) True

Easy explanation: According to the area-velocity relation for a quasi one-dimensional flow, the relation is given as:

\(\FRAC {DA}{A}\)=(M^2-1)\(\frac {du}{u}\)

For sonic flow, Mach number = 1. Therefore for M=1 we get \(\frac {dA}{A}\)=0, thus sonic flow does exist for an equilibrium reacting NOZZLE flow at the throat.

7.

Which is the Euler’s equation for the quasi – one dimensional flow?(a) dp = \(\frac {ρ}{u}\)du(b) dp = –\(\frac {u}{ρ}\)du(c) dp = -ρudu(d) dp = ρuduThe question was asked in semester exam.This interesting question is from Governing Equations in portion Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Correct answer is (c) dp = -ρudu

To explain I would say: We consider a duct of VARIABLE cross sectional area with two stations 1 and 2, having properties as given in the figure.

Using the momentum equation:

p1A1 + ρ1u\(_1^2\)A1 + \(\int_{A_1}^{A_2}\)pdA = p2A2 + ρ2u\(_2^2\)A2

We get,

pA + ρu^2A + pdA = (p + dp)(A + dA) + (ρ + dρ)(u + du)^2 (A + dA)

pA + ρu^2A + pdA = pA + pdA + Adp + dpdA + ρu^2 + (ρdu^2 + 2ρudu + dρu^2 + dρdu^2 + 2dρudu)(A + dA)

SINCE the conditions at STATION 1 are: p, ρ, A and conditions at station 2 are (p + dp), (ρ + dρ), (A + dA).

The product of differentials dPdA, dρ(du)^2(A + dA) are negligible thus are ignored.

The resulting equation is:

AdP + Adρu^2 + ρu^2dA + 2ρuAdu = 0 ➔ eqn 1

The continuity equation is given by:

d(uρA) = 0

Expanding this we get,

ρudA + ρAdu + Audρ = 0

Multiplying the above equation by u on both sides we get:

ρu^2dA + ρuAdu + Au^2dρ = 0 ➔ eqn 2

Subtracting eqn 2 from eqn 1, we get the DIFFERENTIAL equation for the quasi one – dimensional flow:

dp = -ρudu

8.

In which of these conditions there’s no formation of shock wave inside a convergent – divergent nozzle?(a) Overexpanded(b) Underexpanded(c) Fully expanded(d) Fully underexpandedI have been asked this question by my college director while I was bunking the class.I'd like to ask this question from Nozzles topic in portion Quasi-One-Dimensional Flow of Aerodynamics

Answer»

The correct answer is (c) Fully expanded

Explanation: When the NOZZLE is fully expanded i.e. when the ambient PRESSURE is EQUAL to the exit pressure of the nozzle, there no formation of shock WAVES. In case of underexpanded nozzle, there are expansion waves formed at the tip of the nozzle exit and in case of overexpanded nozzle, there’s formation of oblique shock waves at the tip.

9.

Why is the diffuser throat area greater than the nozzle throat area?(a) To reduce speed(b) To maintain constant mass flow rate(c) Rise in entropy within diffuser(d) Rise in entropy within nozzleI had been asked this question in a job interview.Enquiry is from Quasi-One-Dimensional Flow Diffusers topic in chapter Quasi-One-Dimensional Flow of Aerodynamics

Answer»

The correct ANSWER is (c) RISE in entropy within diffuser

Easiest explanation: In a supersonic wind tunnel, there are two throats present. One is that of the NOZZLE which is known as the first throat which has sonic speed with CORRESPONDING area as A*. The second throat is that of the diffuser which is always greater than the first throat because there’s an INCREASE in entropy due to the presence of shock waves.

10.

Oblique shock diffuser has a better pressure recovery than a normal shock diffuser.(a) True(b) FalseThe question was posed to me in examination.My query is from Quasi-One-Dimensional Flow Diffusers in portion Quasi-One-Dimensional Flow of Aerodynamics

Answer»

The correct option is (a) True

The best explanation: In an oblique shock diffuser, the ACCELERATED flow is slowed down by a SERIES of oblique shock waves followed by SLOWING down of the flow by a weak normal wave at the end of the diffuser. THEREFORE, the STATIC pressure at the exit of the diffuser is equal to p∞. The pressure recovery in case of an oblique shock diffuser is greater because of lower total pressure loss compares to the normal shock diffuser.

11.

What is the minimum area of a duct known as?(a) Throat(b) Minimum area duct(c) Convergent duct(d) Divergent ductThe question was asked in final exam.Enquiry is from Area-Velocity Relation topic in portion Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Correct OPTION is (a) THROAT

To ELABORATE: In a nozzle which is designed to achieve supersonic speed, there’s both converging and diverging SECTION which is used to accelerate the flow. There is a minimum area point in the duct where Mach number REACHES 1. This minimum area place in a duct is known as the throat.

12.

According to the energy equation, which of these properties remain constant along the flow?(a) Total enthalpy(b) Total entropy(c) Kinetic energy(d) Potential energyThe question was posed to me by my college professor while I was bunking the class.My question comes from Governing Equations in portion Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Correct option is (a) Total enthalpy

To explain: The energy EQUATION STATED for steady quasi – one – dimensional flow is given by h1 + \(\frac {u_1^2}{2}\) = H2 + \(\frac {u_2^2}{2}\). According to this FORMULA which is derived for the ADIABATIC flow, the total enthalpy remains constant (h0 = 0).

13.

What causes the flow properties to vary in quasi – one – dimensional flow?(a) Cross – sectional area(b) Normal shock(c) Head addition(d) Frictional dragThe question was posed to me in an international level competition.My query is from Governing Equations in section Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Correct CHOICE is (a) Cross – SECTIONAL area

Explanation: In case of quasi – one dimensional flow the flow PROPERTIES keep changing along the DISTANCE x due to the varying cross – sectional area (A) which is in contrast to the one – dimensional flow. In that, the area REMAINS constant thus, the flow properties change fir to the presence of shock wave friction and heat addition or removal.

14.

What is the momentum equation for a quasi – one dimensional flow?(a) p1A1 + ρ1u\(_1^2\)A1 + \(\int_{A_1}^{A_2}\)pdA = p2A2 + ρ2u\(_2^2\)A2(b) p1A1u1+ ρ1u\(_1^2\)A1 + \(\int_{A_1}^{A_2}\)pdA = p2A2u2+ ρ2u\(_2^2\)A2(c) p1A1 + ρ1u\(_1^2\)A1 = p2A2 + ρ2u\(_2^2\)A2(d) p1A1u1+ ρ1u\(_1^2\)A1 = p2A2u2+ ρ2u\(_2^2\)A2This question was posed to me in unit test.The question is from Governing Equations in section Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Right option is (a) p1A1 + ρ1u\(_1^2\)A1 + \(\int_{A_1}^{A_2}\)pdA = p2A2 + ρ2u\(_2^2\)A2

To explain: The integral form of the momentum equation is given by:

∯S(ρV.dS)V = -∯SpdS

In order to find the x – COMPONENT of this the equation becomes:

∯S(ρV.dS)u = -∯SpdSx

Where, pdSx is the x component of PRESSURE

u is the velocity

On the control surfaces of the streamtube, V.dS = 0 because they are streamlines. At 1, A1, V, dS are in opposite direction thus they are negative. This results in the left side of the equation to be – ρ1u\(_1^2\)A1 + ρ2u\(_2^2\)A2.

For the right side of the equation, it is –(-p1A1 + p2A2). Negative SIGN is because at A1, dS points to the left and is negative.

For the upper and lower surfaces of the control volume, pressure integral becomes:

 – \(\int_{A_1}^{A_2}\) – pdA = \(\int_{A_1}^{A_2}\)pdA

Where the negative sign is because the dS points to the left.

This results In the equation to be:

 – ρ1u\(_1^2\)A1 + ρ2u\(_2^2\)A2 = -(-p1A1 + p2A2 ) + \(\int_{A_1}^{A_2}\)pdA

On rearranging the terms we GET:

p1A1 + ρ1u\(_1^2\)A1 + \(\int_{A_1}^{A_2}\)pdA = p2A2 + ρ2u\(_2^2\)A2

15.

Which of these conditions result in underexpanded nozzle?(a) Pe = Pa(b) Pe > Pa(c) Pe < Pa(d) Pe

Answer»

The correct CHOICE is (b) Pe > PA

The BEST explanation: In case of UNDEREXPANDED NOZZLE, the exit pressure is greater than the ambient pressure Pe > Pa. This leads to formation of expansion wave at the tip of the nozzle and the flow is capable of more expansion.

16.

What happens to the mass flow rate if the reservoir pressure is doubled?(a) Doubled(b) Remains same(c) Becomes half(d) Becomes one – fourthI got this question in a national level competition.This intriguing question comes from Nozzles in section Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Right choice is (a) DOUBLED

The explanation: The mass FLOW rate depends on the INLET stagnation pressure, temperature and throat area by the relation:

\(\dot {m} ∝ \frac {p_0 A^*}{\sqrt {T_0}} \)

Thus, when the resrvoic pressure is doubled, the mass flow rate through the nozzle also doubles as it is directly proportional to it.

17.

For which of these flows do we need a divergent duct to increase the velocity of the flow?(a) Subsonic flow(b) Supersonic flow(c) Hypersonic flow(d) Sonic flowThe question was posed to me in an interview.This interesting question is from Area-Velocity Relation in chapter Quasi-One-Dimensional Flow of Aerodynamics

Answer»

The correct option is (b) SUPERSONIC flow

Easy explanation: The area-VELOCITY relation is given by:

\(\frac {dA}{A}\)=(M^2-1)\(\frac {du}{U}\)

According to this formula, for supersonic flows the VALUE of M^2-1 is positive since M > 1. Thus, with INCREASING cross-sectional area, the velocity increases. Increasing area is achieved by convergent duct.

18.

For a subsonic flow, what should be the value of dA to get flow acceleration?(a) Zero(b) Negative(c) Positive(d) OneI have been asked this question in an interview for job.This interesting question is from Area-Velocity Relation in portion Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Correct answer is (b) Negative

The best I can explain: According to the area-velocity RELATION for a QUASI one-dimensional flow, when the flow is subsonic Mach NUMBER is LESS than 1 resulting in the quantity M^2-1 being negative. Therefore for achieving ACCELERATED flow, dA has to be negative.

19.

What happens if the second throat area is larger than the starting value when the wind tunnel starts and the reservoir pressure value is opened?(a) Normal shock is swallowed by diffuser(b) Normal shock remains upstream of diffuser(c) Throat area has no effect(d) Normal shock is generated at the inletI had been asked this question in an international level competition.I need to ask this question from Quasi-One-Dimensional Flow Diffusers in portion Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Right option is (a) Normal SHOCK is swallowed by diffuser

Best explanation: When the wind TUNNEL is initially started, there’s a pressure difference that is generated rapidly creating a transient flow which is often very complex. The starting process USUALLY leads to the formation of the normal shock wave which is PROPAGATED throughout the duct (from nozzle to the diffuser).

If the throat area of the diffuser is not large enough, the normal shock remains upstream of the diffuser and the wind tunnel is unable to start properly. On the other hand, when the second throat area is larger than the starting value, the normal shock is able to pass through the diffuser/swallowed by the diffuser resulting in proper FUNCTIONING of the wind tunnel.

20.

What happens in case of a choked flow?(a) When flow becomes supersonic at the throat(b) When flow is sonic and mass flow remains constant at the throat despite reducing exit pressure(c) When the exit pressure is reduced to a point where the flow becomes subsonic at throat(d) Normal shock is created at the inlet of the nozzleI got this question by my school teacher while I was bunking the class.Origin of the question is Nozzles topic in section Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Right OPTION is (b) When flow is sonic and mass flow remains constant at the THROAT despite reducing exit pressure

The best I can EXPLAIN: When we REDUCE the exit pressure, there comes a point when the Mach number becomes 1 at the throat i.e. the flow is sonic. The mass flow remains constant and the flow becomes frozen upstream of the throat. This condition where after reaching sonic flow at the throat, and despite reducing the exit pressure, the mass flow remains constant is called choked flow.

21.

The area – Mach number relation yields how many solution(s) for a given Mach number?(a) 1(b) 2(c) 3(d) 0I got this question in an international level competition.I'm obligated to ask this question of Nozzles topic in division Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Correct option is (b) 2

To explain I would say: The AREA – Mach relation which is the ratio of LOCAL area to throat area as a function of Mach number yields two solutions for a GIVEN Mach number. One is a SUBSONIC value and the other is the corresponding supersonic value. That value that has to be chosen for a specific Mach number depends on the inlet and exit pressure of the duct.

22.

The governing equations for quasi – one – dimensional flow is used to find properties of flow in a nozzle.(a) True(b) FalseI got this question in final exam.This intriguing question comes from Governing Equations in portion Quasi-One-Dimensional Flow of Aerodynamics

Answer»

The correct answer is (a) True

The BEST EXPLANATION: The three governing equations for quasi – one – dimensional flow is used to compute properties such as pressure, enthalpy, density of a flow inside a nozzle or a diffuser. Apart from this the AREAVELOCITY relation also helps in UNDERSTANDING the physics of supersonic/subsonic flow.

23.

If the given conditions for a nozzle are P01 = 1 atm, Pe = 0.3143 atm, then what is the ratio of exit area to throat area?(a) 1.15(b) 1.5(c) 1.25(d) 1.115The question was posed to me in unit test.This interesting question is from Nozzles topic in chapter Quasi-One-Dimensional Flow of Aerodynamics

Answer» RIGHT choice is (d) 1.115

Explanation: Given, P01 = 1 ATM, Pe = 0.3143 atm

To CALCULATE – \(\frac {A_e}{A^*}\)

Stagnation pressures remain same P01 = P0e

\(\frac {P_{0e}}{P_e} = \frac {1}{0.3143}\) = 3.182

For \(\frac {P_{0e}}{P_e}\) = 3.182 we GET Me = 1.4 (Using gas table)

For Me = 1.4, we get \(\frac {A_e}{A^*}\) = 1.115 (Using gas table)
24.

What is the entropy relation between the entry and exit of an actual diffuser?(a) s1 = s2(b) s1 > s2(c) s1 < s2(d) s1 s2 = 1The question was asked in an online quiz.I'm obligated to ask this question of Quasi-One-Dimensional Flow Diffusers in portion Quasi-One-Dimensional Flow of Aerodynamics

Answer»

The correct answer is (C) s1 < s2

The explanation is: The FLOW DIFFUSES to a slower velocity when the flow interacts with the oblique shock waves inside the diffuser. This causes the diffuser to have a normal shock wave at the end. The ENTROPY of the exit is therefore higher than the entropy of the inlet SEGMENT.

25.

For a flow in a duct, what is Mach number a function of?(a) Local duct area to sonic throat area(b) Sonic throat area to local duct area(c) Local duct area to convergent duct area(d) Local duct area to divergent duct areaI have been asked this question in homework.I would like to ask this question from Nozzles in division Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Correct choice is (a) Local duct area to sonic throat area

To explain: On OBSERVING the area – Mach relation for a FLOW INSIDE a duct, we notice that the Mach number at a point in a duct is a function of ratio of local duct area to the sonic throat area.

M = f(A/A^*)

26.

What is the role of the diffuser?(a) Increase the flow velocity after test section(b) Decrease the flow velocity after test section(c) Increase the flow velocity inside test section(d) Decrease the flow velocity inside the test sectionThe question was posed to me by my school principal while I was bunking the class.I'd like to ask this question from Quasi-One-Dimensional Flow Diffusers topic in division Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Right answer is (b) Decrease the flow velocity after test section

The EXPLANATION is: Diffuser is a duct used mostly in the supersonic wind tunnel in order to slow down the HIGH flow velocity post test section to a lower velocity at the diffuser’s EXIT before EXHAUSTING it to the atmosphere.

27.

In case of the formation of shock in the divergent section of a C – D nozzle, the flow remains isentropic.(a) True(b) FalseI have been asked this question during an interview for a job.My question comes from Nozzles topic in chapter Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Correct option is (b) False

For explanation I would say: Usually the flow in the nozzle is CONSIDERED to be adiabatic because there is no heat TRANSFER. But when we try to achieve SUPERSONIC flow, there is formation of shock waves. Therefore the region between the THROAT the exit of the divergent nozzle does not have isentropic flow.

28.

Which of these properties remain constant in the ideal isentropic supersonic diffuser?(a) Total pressure(b) Velocity(c) Mach number(d) Mass flowI had been asked this question in an international level competition.My question is from Quasi-One-Dimensional Flow Diffusers topic in section Quasi-One-Dimensional Flow of Aerodynamics

Answer»

The correct option is (a) TOTAL pressure

For explanation: Isentropic SUPERSONIC diffusers have a constant entropy throughout the diffuser duct. Since the entropy is constant, the total pressure along is the duct is also constant. Although this is an ideal case and in reality there are some pressure losses OCCURRING due to the formation of shock WAVES.

29.

Why is a variable – geometry diffuser used?(a) Ease in manufacturing(b) Higher efficiency(c) More mass flow rate(d) InexpensiveI had been asked this question by my college director while I was bunking the class.The above asked question is from Quasi-One-Dimensional Flow Diffusers in division Quasi-One-Dimensional Flow of Aerodynamics

Answer»

The correct ANSWER is (B) Higher efficiency

Easiest explanation: In the case of fixed – geometry diffuser, the SECOND throat area is kept larger than the first throat area so that there is no starting problem in the wind tunnel but it does not operate at its maximum efficiency.

Variable – geometry diffuser on the other hand can vary the throat area by hydraulic or mechanical means. The second throat area at the start of the OPERATION is kept high enough so that the normal shock is able to pass through the diffuser and there is no starting problem. Once the wind tunnel starts working, its throat area is reduced so that it OPERATES with a higher efficiency.

30.

What is the exit Mach number if the convergent nozzle is choked?(a) 0(b) 1(c) 0.5(d) 1.5This question was addressed to me during an interview.My question comes from Nozzles in section Quasi-One-Dimensional Flow of Aerodynamics

Answer»

The correct CHOICE is (B) 1

To EXPLAIN I would say: In case of a convergent nozzle, when the flow is choked the EXIT Mach number is 1. In order to check if the nozzle is operating at CHOKING conditions, we compare the actual pressure ratio to the critical pressure ratio. When the actual pressure ratio is larger than the critical pressure ratio, the nozzle is considered to be choked.

31.

What happens to the velocity of the supersonic flow in the convergent duct?(a) Decreases(b) Increases(c) Remains the same(d) Changes periodicallyThis question was posed to me in homework.I'd like to ask this question from Area-Velocity Relation topic in section Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Right choice is (a) DECREASES

The best I can explain: Since the supersonic flows have Mach number greater than 1, the value of M^2-1 is positive. ACCORDING to the area-velocity relation, for a CONVERGENT duct in which dA is NEGATIVE, the velocity decreases.

32.

Total pressure loss in a normal shock diffuser is less than the oblique shock diffuser.(a) True(b) FalseThe question was asked during an online exam.My question is based upon Quasi-One-Dimensional Flow Diffusers in section Quasi-One-Dimensional Flow of Aerodynamics

Answer»

The CORRECT answer is (b) False

Easiest explanation: In case of an oblique shock diffuser, the total PRESSURE DROP across multiple oblique hocks followed by a weak normal shock is less than a strong normal shock in case of normal shock diffuser. This is why it is preferred to opt for an oblique shock diffuser that manages to SLOW down the accelerated flow with lesser pressure loss.

33.

What is the differential form of energy equation for quasi one – dimensional flow?(a) dh – u^2du = 0(b) dh – udu = 0(c) dh + u^2du = 0(d) dh + udu = 0I got this question in an interview.I need to ask this question from Governing Equations topic in chapter Quasi-One-Dimensional Flow of Aerodynamics

Answer»

The CORRECT option is (d) dh + udu = 0

Best explanation: The energy equation for quasi ONE – dimensional flow is given by:

H + \(\frac {u^2}{2}\) = constant

On differentiating the above equation we arrive at the DIFFERENTIAL energy equation for the quasi one – dimensional flow:

dh + udu = 0

34.

Which of this conditions is necessary to achieve flow in a nozzle?(a) \(\frac {P_e}{P_0}\) < 1(b) \(\frac {P_e}{P_0}\) > 1(c) \(\frac {P_e}{P_0}\) = 1(d) \(\frac {P_e}{P_0}\) = 0The question was asked in an interview for internship.I need to ask this question from Nozzles topic in division Quasi-One-Dimensional Flow of Aerodynamics

Answer»

The correct answer is (a) \(\frac {P_e}{P_0}\) < 1

The BEST explanation: If the STAGNATION pressure at the INLET is equal to the exit pressure, then there will be no flow in the nozzle as there is no pressure difference for the flow to move. In order to accelerate the air, the pressure difference has to be created by having pe < p0.

Thus the condition to ACHIEVE an accelerated flow inside a nozzle is: \(\frac {P_e}{P_0}\) < 1

35.

What is the differential form of momentum equation for the quasi one – dimensional flow known as?(a) Froude equation(b) Euler’s equation(c) Kelvin’s equation(d) Bernoulli’s equationI had been asked this question in an online quiz.Query is from Governing Equations in section Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Right choice is (B) Euler’s equation

To elaborate: The DIFFERENTIAL form of momentum equation for the QUASI one – dimensional flow is given by:

DP = – ρudu

This is KNOWN as Euler’s equation which is derived from the momentum equation.

36.

What is the diffuser efficiency for supersonic flow?(a) ηD = 1(b) ηD > 1(c) ηD < 1(d) ηD = 1/2I got this question in exam.Question is taken from Quasi-One-Dimensional Flow Diffusers topic in portion Quasi-One-Dimensional Flow of Aerodynamics

Answer» CORRECT answer is (b) ηD > 1

For explanation: The diffuser efficiency is given by the RATIO of actual total pressure ratio across the diffuser to the total pressure ratio of a hypothetical normal shock wave at test section Mach number. For a supersonic test section Mach number, the diffusers perform better than the normal shock, thus the numerator of the ratio is greater than the denominator, HENCE ηD > 1.
37.

Which of these phenomena attenuates the advantages of greater pressure recovery in an oblique shock diffuser?(a) Abrupt change of convergent – divergent sections(b) Shock wave interaction with walls(c) Isentropic flow(d) Presence of normal shockI got this question during an online interview.I'm obligated to ask this question of Quasi-One-Dimensional Flow Diffusers in section Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Right answer is (b) SHOCK wave interaction with WALLS

The explanation: The viscous boundary layer inside the diffuser wall interacts with the shock wave. This creates an ADDITIONAL loss in total pressure which attenuates.

 In real life, oblique shock diffusers have viscous flow. The PRESENCE of shock waves inside the diffuser leads to interaction with the viscous boundary layer of the diffuser walls which leads to additional pressure losses. There’s also friction INVOLVED which makes oblique shock diffusers far from the ideal diffusers which have no total pressure losses.

38.

The trends of velocity change in a duct for both subsonic and supersonic flow are identical.(a) True(b) FalseI got this question by my college professor while I was bunking the class.My doubt stems from Area-Velocity Relation in chapter Quasi-One-Dimensional Flow of Aerodynamics

Answer»

Right option is (b) False

Explanation: For a flow in a DUCT, both supersonic and SUBSONIC flows show OPPOSITE trends. For a subsonic flow (M < 1), the velocity increases in a convergent duct and DECREASES in the DIVERGENT duct. On the other hand, for a supersonic flow (M > 1), the flow increases in a divergent duct and decreases in the convergent duct.