One should look into hypersonic wind tunnels, M > 5, which is an arbitrary cutoff, but a convention.shreddinglicks said:Summary:: Shock Tunnel pressures
Mach 6
How would I do that? Maybe my logic is wrong. Don't I need to know the temperature to get the viscosity?boneh3ad said:The typical test section pressures in a shock tunnel can vary greatly depending on application. In your case, it sounds like you can start with your desired ##Re## and work backward. What length scale are you using for the ##Re## you cited? If you are referencing free-stream conditions, it would be more appropriate to cite unit ##Re##.
shreddinglicks said:How would I do that? Maybe my logic is wrong. Don't I need to know the temperature to get the viscosity?
The way I have done it is:
1. Create a desired pressure ratio.
2. Calculate incident shock mach.
3. Calculate pressure, density, temperature ratios of incident shock.
4. Calculate reflective shock mach.
5. Calculate pressure, density, temperature ratios of reflective shock.
6. Obtain reservoir properties.
7. Use isentropic relations to obtain properties at nozzle outlet where mach = 6.
8. Get shock property ratios at plate.
9. Calculate pressure, density, temperature ratios at plate edge
10. I use the Sutherland eq for viscosity and velocity is found from m = u/sqrt(gamma*287*Tp)
287 is air gas constant and Tp is the temperature at the plate. This gives me the unit Reynolds number, rho*u/mu
I haven't thought of that. I'll try a script where I'll pick a Reynolds number and work my way to the pressure ratio.boneh3ad said:Sure, but generally if you are designing a wind tunnel, you are starting with your desired free-stream conditions. If you know what ##Re^{\prime}## (or altitude or whatever target you are shooting for that stands in for pressure/density) and ##h_0## you want, you can set your desired pressure and temperature based on that and work backward. If you aren't shooting for high-enthalpy (seems unlikely if you are designing a reflected shock tunnel), then just enough ##T_0## to avoid liquefaction is sufficient.
I tried to work backwards. I chose a Reynolds number and varied the pressure to obtain it. Then worked backwards:boneh3ad said:Sure, but generally if you are designing a wind tunnel, you are starting with your desired free-stream conditions. If you know what ##Re^{\prime}## (or altitude or whatever target you are shooting for that stands in for pressure/density) and ##h_0## you want, you can set your desired pressure and temperature based on that and work backward. If you aren't shooting for high-enthalpy (seems unlikely if you are designing a reflected shock tunnel), then just enough ##T_0## to avoid liquefaction is sufficient.
If I assume an incident shock mach number. I am able to work my way back to p4/p1 and values of the pressures.shreddinglicks said:I tried to work backwards. I chose a Reynolds number and varied the pressure to obtain it. Then worked backwards:
1. calculated the shock at the plate.
2. Obtained property ratios.
3. With the free stream properties I used the isentropic relations to get ratios of free stream and reservoir properties at the nozzle.
4. The equation I have for the reflected shock is a function of specific heat ratio and incident shock mach number so I am stuck.
True, but that would be another topic of focus. Astronuc, mentioned a wiki article stating early designs achieving pressures of 200 MPa. I am interested in what modern designs are capable of.boneh3ad said:Ultimately, this is a design problem, so you have more than just free-stream conditions constraining you, for example, strength of materials. Ultimately, you might not want your driver tube to go over a certain pressure or temperature for safety reasons, so that gives you another constraint or two.
shreddinglicks said:True, but that would be another topic of focus. Astronuc, mentioned a wiki article stating early designs achieving pressures of 200 MPa. I am interested in what modern designs are capable of.
LENS at CUBRC claims to achieve Reynolds number of 10^8.boneh3ad said:I wouldn't put any weight in Wikipedia articles like that. You can follow the citations in them and see where they lead, but the translation by random people on topics like this is often poor.
You might checking out the pages for various well known shock tunnels around the world. Some examples:
T5 at Caltech
HIEST at JAXA
T4 at UQ
LENS at CUBRC
HEG at DLR Göttingen
That actually sounds reasonable. In some ways, they knew more about this stuff in the 1960‘s. At a certain point, you will be limited by material strength of the barrel, so I would be surprised by anything over 1GPa in a non-disposable system.shreddinglicks said:True, but that would be another topic of focus. Astronuc, mentioned a wiki article stating early designs achieving pressures of 200 MPa. I am interested in what modern designs are capable of.
shreddinglicks said:LENS at CUBRC claims to achieve Reynolds number of 10^8.
caz said:That actually sounds reasonable. In some ways, they knew more about this stuff in the 1960‘s. At a certain point, you will be limited by material strength of the barrel, so I would be surprised by anything over 1GPa in a non-disposable system.
There is a modern book on shock tubes
https://www.amazon.com/dp/3319237446/?tag=pfamazon01-20
I have that book.caz said:That actually sounds reasonable. In some ways, they knew more about this stuff in the 1960‘s. At a certain point, you will be limited by material strength of the barrel, so I would be surprised by anything over 1GPa in a non-disposable system.
There is a modern book on shock tubes
https://www.amazon.com/dp/3319237446/?tag=pfamazon01-20
You will probably get a better response if you put this in a new posting.shreddinglicks said:Thanks to everyone who replied. I have one final question. I've been searching the net but can not find any freely available literature. Can someone give me a quick lesson on boundary layer instability and its frequencies? I have an equation that claims to scale the instability frequency by:
F = U/2*delta
U is leading edge velocity
delta is layer thickness
What information does this give me? Does this tell me the likelihood of transition from laminar to turbulence?
Will do.caz said:You will probably get a better response if you put this in a new posting.
A shock tunnel is a type of wind tunnel used to study high-speed flows and the effects of shock waves on objects. It consists of a long tube filled with a gas, typically air, and a test section where models or objects can be placed for experimentation.
In a shock tunnel, pressures are typically measured using pressure transducers or sensors. These devices convert the pressure into an electrical signal that can be read and recorded by a computer or data acquisition system.
The main purpose of measuring pressures in a shock tunnel is to understand the aerodynamic forces and flow characteristics of objects in high-speed flows. This information is crucial for the design and development of aircraft, rockets, and other high-speed vehicles.
The typical pressures in a test section of a shock tunnel can vary greatly depending on the specific conditions and experiments being conducted. However, they can range from a few thousand to millions of pascals (Pa), which is equivalent to a few to several hundred atmospheres of pressure.
The pressures in a shock tunnel are significantly higher than those found in real-life high-speed flows, as the gas in the tunnel is compressed and heated to simulate the conditions of hypersonic flight. However, the flow characteristics and aerodynamic forces observed in a shock tunnel can still provide valuable insights and data for real-life applications.