Hypersonics - Science topic

in my experiments I used the PVD (Physical Vapor Deposition) technique.

Hypersonic vehicles, traveling at speeds greater than Mach 5 (approximately 3,836 miles per hour), encounter several significant thermal and mechanical loads that impact composite materials.

Here are some specific aspects of these loads:

Thermal Loads:

a. Aerodynamic Heating: Hypersonic flight generates intense aerodynamic heating due to the high speeds and air compression. The friction between the vehicle and the surrounding air leads to a substantial rise in temperature, causing thermal loads on the composite materials.

b. Thermal Gradients: The extreme thermal environment of hypersonic flight results in significant temperature gradients across the vehicle structure. This creates thermal expansion and contraction within the composite materials, which can induce internal stresses and potentially affect their mechanical behavior.

c. Thermal Shock: Rapid heating and cooling cycles, caused by the transient nature of hypersonic flight, subject the composite materials to thermal shock. This can lead to localized temperature variations and thermal stresses, potentially affecting their structural integrity.

Mechanical Loads:

a. Aerodynamic Forces: Hypersonic vehicles experience intense aerodynamic forces due to the high speeds and air density. These forces generate significant mechanical loads on the composite structure, including bending, compression, tension, and shear.

b. Vibrations: Hypersonic flight can induce vibrations and oscillations in the vehicle structure. These dynamic loads impose additional mechanical stresses on the composite materials, which may affect their fatigue resistance and overall performance.

c. Shock Waves: Hypersonic flight involves the formation and interaction of shock waves. The interaction of shock waves with the vehicle's surface can result in high-pressure loads and impulsive forces, imposing mechanical stresses on the composite materials.

Understanding and analyzing these thermal and mechanical loads is crucial for designing composite materials that can withstand the extreme conditions of hypersonic flight. Advanced computational models and simulation techniques are used to predict and study the behavior of composite materials at different length scales, allowing researchers to assess their mechanical response, thermal behavior, and failure mechanisms accurately.

Typical re-entry Mach number for Apollo flights was M=24. This is the reason for the very thick metal shield that was used to protect the cabin. This shield would simply evaporate (evaporation cooling). The gas temperature would reach incredibly high temperature. From Bernoulli one finds without assuming ionization or dissociation of air To/T=1+0.2M^2=181 at M=30. The stagnation temperature would reach 50.000 K for surrounding temperature T=300 K. Dissociation and ionization would lower this to temperature of the order of 15.000 K. The wall recovery temperature would be of that order of magnitude. Hence a conventional rocket with M=30 is almost impossible. Even for a scramjet at M=7 or M=8 we expect already temperatures of a few thousand degrees (after dissociation). Indeed it is extremely difficult to keep such an engine "alive" (even for short times). The great advantage of scramjet above a normal rocket is that it carries the fuel but gets the oxygen from the surrounding air. This dramatically decreases the engine weight at take-off. However, such engines are currently launched from an aircraft, which also reduces the power for take-off.

Hi, I solved the same equation and described some ideas here: . The equation appears to be just fine. I am attaching the RK routine (Fortran). Please, let me know if it helps.

Thanks a lot Sir.

One more doubt, in case of 2d axissymetric analysis over a blunt body (Orion CEV) , what could be the reference area value inorder to calculate drag coefficient?

My sincere apologise Sir,

I am actually new to this. So i don't know what to mention and all. Hope you will understand

Density based solver with fluid as air (ideal gas density and sutherland function for viscosity)

Turbulence model - SST K-omega

Pressure farfield as freestream with mach 6 and pressure 1064 pa and temperature 234 K

I have used the same as reference values too.

Flux type - ROE FDS

Green gauss node based discretisation scheme

CFL number 0.5

Please let me know if anyelse information is needed.

Omkar Singh Kushwaha Thank you Professor.

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Active cooling, such as transpiration cooling, in combination with UHTC is also a possible solution for particular missions. In the case of transpiration cooling, the UHTC wall would be porous. One of the interesting aspects here is that when an inert gas is injected though the pores, it can protect the UHTC from the outer hot gas and thereby prevent or reduce oxidation. As a result, the full potential of UHTC's high melting point can be exploited. A number of papers have been published on this from different groups.

Dear Shantanu P. Gawande, these bibliographic material I Guess worth to read. My Regards

Correction: Replace

Inspection shows that upon u = c, u' =v, as it should be. The speed of light is invariant.

by

Inspection shows that upon u = c, u' =c, as it should be. The speed of light is invariant.

I would not say that the efforts have failed outright. Significant research has been conducted on the topic and many things have been learned.

One of the main theoretical challenges (something that challenges researchers before even considering any sort of development) is the presence of strong non-equilibrium phenomena. Because the aircraft are meant to travel at such high speeds, they encounter extremely strong shockwaves which lead to high temperatures surrounding the vehicle. This can cause chemical reactions such as dissociation and ionization as well as thermal non-equilibrium, processes that make it extremely difficult to analyze these flows from a simulation point of view, for a slew of reasons that I won't get into. These conditions are also very difficult and costly to recreate in an experimental setting.

On the applications side, there were (and still are) many technological challenges facing the development of these vehicles. For example, the extremely high temperatures that they are bound to encounter need to be mitigated through advanced materials and thermal protection systems. However, things are starting to turn around due to advances in high-temperature ceramics and other materials, as well as improvements in manufacturing processes.

low-supersonic commercial travel had already been achieved a while back when the Concorde flew. However, I believe that the construction and operating costs were prohibitive. Current advances may make these applications more profitable.

In general CFD has reached a certain level of maturity; however, work can still be done in extending existing codes to consider hypersonic phenomena and performing verification and validation. Furthermore, investigations into more advanced topics such as aerodynamic shape optimization, unsteady flows, and coupled fluid-thermal-structural modeling are very popular.

Interesting question

Hi Anton,

those data were collected from at least 4 wind tunnels it seems:

-Langley 20 inch Mach 6

-Mach 6 high Re number

-Mach 8 variable density hypersonic tunnel

-Langley 22-inch helium tunnel

Maybe you can try accessing this article, perhaps this one is not restricted for you:

Hope this helps,

David

Hi Jason,

The following article may help you.

Samuel,

I believe you should write your own UDF.

I send you a PDF file as attached file :

"CFD Modeling and Analysis of an Arc-jet facility using

ANSYS Fluent"

Regards.

Hello Samuel,

the answer is yes if you use compressible DES being able to capture large temperature gradients (omitting chemical reactions in a first step)and shocks. But note also that this can only hold if the Knudsen number is not too large, i.e. the capsule flies already in an environment with significant gas density. But still then the Reynolds number is relatively low, and the boundary layers are often laminar, only free shear layers may cause large-scale flow unsteadiness. Hence try to compute without turbulence model (but with shock capturing) and check for alterations of the results.

The RNG k-epsilon model is a good one for your case and make sure that you use and enhanced wall treatment to get a much better prediction of transitional flows

It depends on your attention problem. If you're going to compare the shock configurations with the experimental results, you'd better:::

Inlet and Outlet as Pressure far field, and the pressure and temperature are given as the incoming value. The wall is better set as Symmetric boundary to avoid a shock/boundary interaction. 

Otherwise, you can give a fix-temperature wall condition.

You'd better try it more times, then you will find the best setting.