Intro to Hyp. - Mid Term Review

Question 1

Newtons 2nd law requires acceleration to be expressed in an _____ frame.

Answer 1

Inertial

Source Notes, 2.1

Question 2

What is the physical interpretation of the ballistic coefficient?

Answer 2

Its a measure of an objects ability to overcome air resistance in flight. A higher value implies that a given object can overcome drag forces more efficiently than an object with a lower coefficient.

Dynamics of Atmospheric Re-Entry, F.J. Regan, Pg. 182

Question 3

In regards to defining continuum vs. rarified flow, what parameter is of primary utility?

Answer 3

The Knudsen number.

Kn = λ/L

Where λ is the mean free path and L is a reference length.

Hypersonic Aerothermodynamics, J. Bertin, Pg. 12

Question 4

For the stagnation region, what are the four dominant chemical reactions for equilibrim in order of occurrence with increasing velocity?

Answer 4

1. Vibrational Energy Excited
2. Oxygen Dissocates
3. Nitrogen Dissocates
4. Ionization of Nitrogen and Oxygen

Hypersonic Aerothermodynamics, J. Bertin, Pg. 19 (Fig. 1.14)

Question 5

In a thermally perfect gas, the state variables e and h are determined by what parameter?

Answer 5

Absolute temperature.

Source Notes: 3.3.1

Question 6

The specific heats begin to vary with absolute temperature for air around Mach = __________. Chemical effects begin at aroung Mach = __________.

Answer 6

M = 3
M = 6

Source Notes: 3.3.1

Question 7

True or False:
Following a bow shock the change in entropy (ds) in the shock layer is negligible compared to the boundary layer.

Answer 7

True.

Source Notes: 3.1.2 Hypersonic Gas Dynamics

Question 8

Generally, the continuim approach is valid for a Knudsen number Kn < _________.

Answer 8

0.01

Source Notes: 3.1.2 Hypersonic Gas Dynamics

Question 9

What paramter discussed in class can serve as a measure of the degree of dissociation?

Answer 9

z = R_{mix}/R_{air}

Lecture: 10/31/2023

Question 10

What is the theoretical upper bound for z, where z = R_{mix}/R_{air}?

Answer 10

z = 2.07 ~ 2

Question 11

True or False:
Monotonic gasses only have translational degrees of freedom. There are no vibrational or rotational modes to excite.

Answer 11

True.

Question 12

At what approximate temperature (in Kelvin) does vibrational excitation of diatomic oxygen and nitrogen begin to occur?

Answer 12

1000 - 1500 K

Question 13

At what temperature range, does diatomic oxygen bein to dissociate?

Answer 13

Approximately 2000 - 3000 K

Question 14

At what temperature range does diatomic nitrogen begin to dissociate?

Answer 14

Approximately 3000-4500 K

Question 15

At what temperature (in Kelvin) does ionization generally occur for air?

Answer 15

Approximately 5000 K

Question 16

Why does oxygen dissociation occur before nitrogen?

Answer 16

The dissociation energy for oxygen is much lower than nitrogen (498 vs. 945 kJ/mol) .

Question 17

What are the four primary “real gas effects?”

Answer 17

1. Dissociation
2. Ionization
3. Chemical Reactions
4. Vibrational Activation

Question 18

For the unmodified Newtonian model of aerodynamics, the Cp (pressure coefficient) has a max value of _____, and a specific heat ratio of _______.

Answer 18

2
1

Question 19

For modified newtonian model of aerodynamics, Cp_w < ________.

Note: Cp_w = pressure coefficient at the wall.

Answer 19

2 (which is the cp_max for the unmodified Newtonian model).

Question 20

True or False:
In the modified Newtonian model, the calculation of the pressure coefficient at the wall becomes a function of the specific heat ratio.

Answer 20

True.

Question 21

What are the three primary transport properties that need to be considered in hypersonic flows?

Give the corresponding coefficients for each as they would appear in the equations of motion.

Answer 21

1. Mass diffusion (D for use in Fick’s law)
2. Momentum Diffusion (μ for the dynamic viscosity)
3. Energy Diffusion (κ for use in Fourniers equation)

Question 22

What is one of the primary constraints for hypersonic air-breathing vehicles in terms of it’s trajectory state?

Answer 22

The trajectory must be tailored such that a high dynamic pressure may be maintained. This ensures:
1. Efficient combustion
2. Effective mixing of fuel with air
3. Safe engine cooling
4. Optimal oxygen/fuel ratios

Question 23

What is the non-dimensional paramter that links the viscosity of a medium to its thermal conductivity?

Answer 23

The Prandtl number (Pr)