Hypersonic Heat Exchange

Investigations of Heat Transfer

Heat transfer is investigated in the short-duration (impulse) and long-duration (intermittent) wind tunnels, as well as by computational analysis.

Heat transfer in the short-duration wind tunnels is basically investigated by the thin wall method: microthermocouples 30 ... 40 m in thickness and 02. mm in width are welded to the 0.1 ... 0.2 mm-thick metal wall. Minimum distance between the thermocouples is 0.5mm. When a high spatial resolution is not required, thin calorimeters 2mm in diameter are used. Very small heat fluxes are measured by platinum film gages. Along with heat fluxes, pressure distributions (using gages and pressure sensitive paints — PSP), pressure fluctuations, stagnation pressure (Pitot pressure) are also measured, ordinary and high-speed shadow pictures are made, and concentrations of dust injected into the gas flow to investigate two-phase flows are determined. Owing to small consumption of energy and materials, the test costs in the short-duration wind tunnels are much lower than those in the long-duration wind tunnels. At the same time, a wide range of flow parameters is realized in these wind tunnels. In view of this, a large scope of experimental investigations can be carried out.
The main means of investigating heat transfer in long-duration wind tunnels are thermal sensitive paints (TSP) and surface foil thermocouples. Use is made of melting TSP paints not sensitive to air pressure. The foil surface gage is a thin thermocouple bonded into the model made of heat-insulating material. The spatial resolution of these gages is about 0.5 mm. Special programs are developed to process the heat flux measurement results obtained using TSP paints and surface foil thermocouples. Navier-Stokes equations and boundary layer equations are used for numerical investigations of heat fluxes. A problem of complex heat exchange (heat conduction, convection, emission) is solved using heat fluxes obtained. Non-steady temperatures at a flight vehicle structure are determined.

Investigations of Thermal Protection

Samples of heat-protective materials and small fragments of vehicle structure are tested at TsAGI under conditions approaching the flight conditions:

The wind tunnel T-34 equipped with a 10000 kW arc heater. The total temperature is up to 4000K, the total pressure is up to 40 bar, the test time is up to 180sec. The stagnation pressure ( pressure at the front model point) is up to 8 bar with the flow diameter of 100mm and 1 bar with the flow diameter of 200 mm.
The wind tunnel T-122 equipped with a 1000kW arc heater. The total temperature is up to 5000K, the total pressure is up to 10 bar, the test time is up to 30 min. The heatshield panel under study can be installed in the nozzle wall. In this case, its sizes are as follows: 450 mm ( in the free-stream flow direction) by 200 mm, the thickness is up to 100mm, the surface temperature is up to 1300C, the surface pressure is 0.02 bar. The test panel can also be installed on the surface of a wedge introduced into the flow. Here, the panel sizes are 130 × 130 mm, the thickness is up to 60 mm, the surface temperature is up to 1600C, the surface pressure is up to 0.06 bar.
The wind tunnel is equipped with the device to provide a specified pressure distribution on the surface of the panel under study. This device is used for simulating the hot air flow in a porous heat-shield material. Another device produces the pressure difference between the external and internal panel surfaces which makes it possible to evaluate the effectiveness of the seals commonly placed between the heatshield fragments.
The wind tunnels VAT-104 and VTS equipped with high-frequency induction heaters with the power of, respectively, 240 kW and 860 kW, the flow diameter is 100 mm, the test time is up to 1 hour, the total temperature is up to 7000K, the total pressure is up to 0.7 bar, the stagnation pressure is up to 0.06 bar. Due to absence of electrodes in the heater, these facilities ensure a high air cleanliness and are used to investigate catalycity and chemical erosion of heat-shield materials.
A set of thermo-vacuum chambers of various dimensions and levels of pressure and temperature in them ensures investigations of serviceability of heat protection elements of super- and hypersonic vehicles with reproduction of vibrations and other mechanical loads along flight trajectory.