Intro to Hyp. - Mid Term Review Flashcards
Newtons 2nd law requires acceleration to be expressed in an _____ frame.
Inertial
Source Notes, 2.1
What is the physical interpretation of the ballistic coefficient?
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
In regards to defining continuum vs. rarified flow, what parameter is of primary utility?
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
For the stagnation region, what are the four dominant chemical reactions for equilibrim in order of occurrence with increasing velocity?
- Vibrational Energy Excited
- Oxygen Dissocates
- Nitrogen Dissocates
- Ionization of Nitrogen and Oxygen
Hypersonic Aerothermodynamics, J. Bertin, Pg. 19 (Fig. 1.14)
In a thermally perfect gas, the state variables e and h are determined by what parameter?
Absolute temperature.
Source Notes: 3.3.1
The specific heats begin to vary with absolute temperature for air around Mach = __________. Chemical effects begin at aroung Mach = __________.
M = 3
M = 6
Source Notes: 3.3.1
True or False:
Following a bow shock the change in entropy (ds) in the shock layer is negligible compared to the boundary layer.
True.
Source Notes: 3.1.2 Hypersonic Gas Dynamics
Generally, the continuim approach is valid for a Knudsen number Kn < _________.
0.01
Source Notes: 3.1.2 Hypersonic Gas Dynamics
What paramter discussed in class can serve as a measure of the degree of dissociation?
z = R_{mix}/R_{air}
Lecture: 10/31/2023
What is the theoretical upper bound for z, where z = R_{mix}/R_{air}?
z = 2.07 ~ 2
True or False:
Monotonic gasses only have translational degrees of freedom. There are no vibrational or rotational modes to excite.
True.
At what approximate temperature (in Kelvin) does vibrational excitation of diatomic oxygen and nitrogen begin to occur?
1000 - 1500 K
At what temperature range, does diatomic oxygen bein to dissociate?
Approximately 2000 - 3000 K
At what temperature range does diatomic nitrogen begin to dissociate?
Approximately 3000-4500 K
At what temperature (in Kelvin) does ionization generally occur for air?
Approximately 5000 K
Why does oxygen dissociation occur before nitrogen?
The dissociation energy for oxygen is much lower than nitrogen (498 vs. 945 kJ/mol) .
What are the four primary “real gas effects?”
- Dissociation
- Ionization
- Chemical Reactions
- Vibrational Activation
For the unmodified Newtonian model of aerodynamics, the Cp (pressure coefficient) has a max value of _____, and a specific heat ratio of _______.
2
1
For modified newtonian model of aerodynamics, Cp_w < ________.
Note: Cp_w = pressure coefficient at the wall.
2 (which is the cp_max for the unmodified Newtonian model).
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.
True.
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.
- Mass diffusion (D for use in Fick’s law)
- Momentum Diffusion (μ for the dynamic viscosity)
- Energy Diffusion (κ for use in Fourniers equation)
What is one of the primary constraints for hypersonic air-breathing vehicles in terms of it’s trajectory state?
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
What is the non-dimensional paramter that links the viscosity of a medium to its thermal conductivity?
The Prandtl number (Pr)
