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MAE 3303 COMPRESSIBLE FLOW- EXAM 1 FRQS (QUIZ 1-8)
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MAE 3303 COMPRESSIBLE FLOW- EXAM 1 FRQS (QUIZ 1-8)
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MAE 3303 COMPRESSIBLE FLOW- EXAM 1 FRQS (QUIZ1-8)
What is the definition of a compressible flow? Are all liquid flows incompressible? Are all
gas flows compressible? - Answers-Fluid flow where the density change is very
significant, usually 5% or more. All liquid flows are considered incompressible. Not all gas
flows are considered compressible.
Does M -> 00 imply V -> 00? - Answers-No, if M-> 00, that does not mean V -> 00 because
M= V/a
Above what Mach number will changes in air density exceed 5%? - Answers-When M >
0.3
What are the most important and distinctive effects of compressibility on flow? - Answers-
1. Choking - wherein the duct flow rate is shapely limited by the sonic condition
2. Shock Waves - which are nearly discontinuous property changes in a supersonic flow
How is kinetic energy distinguished from internal energy? - Answers-Kinetic energy is
associated with the directed or bulk motion of the fluid whereas internal is associated with
the random motions of molecules of a system.
What is a reversible process? What common agent is required for irreversibility? -
Answers-No dissipative phenomena occur, like friction, heat transfer, mass diffusion,
shock waves, etc. The common agent required for irreversibility is a significant spatial
gradient of the field.
An isentropic process is always: - Answers-Reversible and adiabatic
State the 1st law of thermodynamics applied to a system. - Answers-head entering a
system, Q + work entering a system, W = change in energy, /\E
Can the entropy of a system ever decrease? If so give an example. Can the entropy of
an adiabatic system ever decrease? If so give an example. - Answers-No and no. A
process will proceed in a direction such that the entropy of the system plus that of its
surroundings always increase, or at best, stay the same.
Name the three governing equations of fluid dynamics: - Answers-1. Mass conservation
2. Momentum conservation
3. Energy conservation
What is the physical interpretation of the time rate of change of a fluid property contained
in a fixed volume in the integral form of governing equations? - Answers-The time rate of
, change of a volume integral represents the accumulation/decumulation of a flow quantity
in the control volume due to flow unsteadiness.
What is the physical interpretation of the surface integral in the integral form of governing
equations? - Answers-The surface integral represents the net efflux of the property across
the control surface.
What is the advantage of the control volume approach over the differential equation
approach for flow analysis? - Answers-It is not necessary to know the details of the flow
inside the control volume in order to compute useful information like thrust and efficiency
of a jet engine.
What is the limitation of the control volume approach? - Answers-It does not predict the
details of the flow within the control volume.
What is the one-dimensional flow assumption? - Answers-At any given section all fluid
properties are constant/uniform across the cross section.
State the energy equation for steady one-dimensional single stream flow. - Answers-h2 -
h1 + ((V2)^2 - (V1)^2)/2 = q + ws
Why does the familiar Bernoulli Equation not hold in a compressible flow? *** - Answers-
The internal energy component is not compatible with compressible flow.
How are stagnation properties defined? How are they determined? - Answers-For a
flowing fluid, stagnation state is defined as a reference state that would exist if the fluid
were decelerated to zero speed relative to an observer. To obtain a unique stagnation
state, the deceleration process must be isentropic without shaft power.
Is there any difference between stagnation property and total property for gas flow? -
Answers-No difference. They are different names for the same concept.
Why does thermodynamics play an important role in the study of compressible flows? -
Answers-The motion of a compressible fluid is directly affected by its thermodynamic
state
What is the principle of state? - Answers-For a simple compressible system, composed
of a single chemical species of gas, the thermodynamic state is completely defined by
two independent state variables.
The thermodynamic state of a unit mass pure substance is determined by how many state
variables? - Answers-Two state variables
State the thermal equation of state. - Answers-p = RT/v = rho*RT
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