Hotshot Wind Tunnel Research Articles

Effect of heat losses in the temperature transducer in measurements in hotshot wind tunnels

Effect of heat losses in the temperature transducer in measurements in hotshot wind tunnels

Specific Features of Flow on Compression Surfaces of a Convergent Air Intake

The results of computational and experimental studies of a model of a hypersonic convergent air intake are presented. Experimental studies were carried out in a hot-shot wind tunnel IT-302M SB RAS at a Mach number M = 5.7 and an angle of attack α = 4 °. Numerical modeling was carried out in a three-dimensional setting in the ANSYS Fluent software package. The calculations were carried out in 4 versions using different turbulence models: k-ɛ standard, RNG k-ɛ, k-ɷ standard and k-ɷ SST. The features of the flow structure are established. The pressure distributions on the compression surfaces and in the air intake channel are obtained. The separated flow at the entrance of the inner channel was studied. It was found that the use of various turbulence models has a significant effect on the size and position of separation. The best agreement between the calculated and experimental data on the level of static pressure was shown by the variant with the k-ɛ standard turbulence model.

Influence of surface sublimation on the stability of the supersonic boundary layer and the laminar–turbulent transition

We report a theoretical study of the properties of a supersonic boundary layer and its linear stability under conditions of surface material sublimation. Calculations were performed for an adiabatic boundary layer for a flat plate with a naphthalene coating at a free-stream Mach number of M = 3 (for the first instability mode disturbances). In the boundary layer, surface sublimation generates a binary mixture flow (air and foreign vapors). This flow is studied using local self-similar boundary layer equations, and it is shown that the rise in the flow stagnation temperature and the corresponding evaporation of the wall material cause significant wall cooling and an increase in the near-wall density of the binary mixture. This modification of the boundary layer profiles leads to a decrease in the disturbance amplification rates. This is confirmed by calculations based on linear stability theory (LST). Boundary-layer stabilization occurs with an increase in stagnation temperature. The influence of surface sublimation on the position of the laminar–turbulent transition was estimated by means of the LST-based eN method. The possibility of increasing the transition Reynolds number by application of the sublimation coating is demonstrated. The results of pilot boundary layer transition experiments performed in a hot-shot wind tunnel are reported. For the first time, a delay in the transition due to the application of a naphthalene coating was experimentally demonstrated. It is also shown that surface sublimation leads to an increase in the growth rates of the second and third instability modes for a Mach 8 boundary layer.

Influence of the relative momentum flux ratio on the mixing of hydrogen jets in an M=4 crossflow

The paper presents the results of numerical simulation of the 3D flows in a plane channel with the abrupt expansion. Sonic hydrogen jets are supplied from two circle orifices located opposite each other on the channel walls before the backward-facing step. The numerical simulations are carried out under the conditions of experiments performed at the hot-shot wind tunnel IT-302M ITAM SB RAS for the following flow parameters: Mach number at the entrance of the channel M = 3.84, the total temperature T0 = 1715 K, and the total pressure P0 = 6.5 MPa. Calculations were performed with a change in the jet supply pressure from 0.4 to 3.6 MPa, which ensures the variation in the jet-to-crossflow momentum flux ratio in the range of J = 0.7 ÷ 6. Mathematical modeling was performed in ANSYS Fluent based on the Reynolds-Averaged Navier-Stokes equations supplemented by the k-ω SST turbulence model. A comparison of the calculated and experimental data on the flow structure, as well as the static pressure distributions on the walls, indicates a satisfactory agreement. The calculated results made it possible to obtain a clearer understanding of the 3D flow structure in the channel and reveal the influence of the injection pressure on the level of mixing.

Correction of inertance of temperature sensing devices in high-speed flow

The influence of the thermocouple calibration method on the reconstruction of the real temperature in impulse wind tunnel with operation duration of up to 100 ms is presented. It is shown that in an impulse set-up allow obtaining a stepwise thermal load with long temperature plateau which enough to determination of instrumental function, necessary for temperature reconstruction. To this aim, the developed technique, based on the application of the solution of the convolution integral equation, was used. It was included the information on the instrumental function, which was obtained from the calibration measurements. In the deconvolution procedure, the signal was first smoothed by splines, the convolution kernel was extracted by the differentiation of smoothed function, and regularization was performed by Kaczmarz algorithm with relaxation parameter. A comparison is made of the temperature reconstruction in the regular mode of hot shot wind tunnel with two different methods for measuring the response of thermocouples to the temperature step: measurement behind the shock wave front and rapid immersion in aluminum melt. It is found that the use of the instrumental function obtained in a wind tunnel allows one to more reliably determine the position of the temperature maximum in real experiment, which corresponds to the physical structure of the flow.

Determination of the Fuel Concentration Distribution in a Supersonic Combustion Chamber

Kerosene concentration distributions measured in the combustion chamber of a hotshot wind tunnel in the attached pipeline regime with the input Mach number of 2.89 are reported. Kerosene is injected through 12 jet injectors at an angle to the flow from the wall upstream of a cavity. The measurements are performed in three cross sections. Data on the kerosene concentration distribution in the initial region of the combustion chamber and its dependence on the ratio of the jet and main flow momenta are obtained. It is demonstrated that the absence of intense combustion in a model combustor under these conditions is caused by the fact that the local equivalence ratios are insufficient for ignition.

Operating safety of a hot-shot wind tunnel with combined test gas heating in stabilization mode

In the present paper, we analyze emergency situations typical of short-duration wind tunnels with electric-arc or combined test-gas heating in the presence of stabilization and diaphragm-rupturing systems, which occur in the case of no discharge initiation in the settling chamber, with the capacitor battery having remained charged during the start of wind-tunnel systems. For avoiding such emergency situations, some additional changes based on using feedback elements are introduced into the wind-tunnel design: the piston of the fast-response valve is made hollow for increasing the volume of the shutoff cavity and for making the release of pressure from this cavity unnecessary; the high-pressure channel, which connects the piston and the piston rod with the settling-chamber cavity, is filled with a liquid and is closed from the side of the settling chamber with a piston; the device for controlled diaphragm breakdown is provided with an external electric circuit intended to control the diaphragm-rupturing process. Those modifications allow subsequent functioning of the wind-tunnel systems only in the presence of heat-supply-induced pressure growth in the settling chamber of the wind tunnel.

On the question of starting conditions for frontal axisymmetric inlets tested in hot-shot wind tunnels

The work presents the results of an analysis of starting conditions for some frontal axisymmetric inlets of internal compression tested at freestream Mach numbers М = 3−8.4 in the hot-shot wind tunnels based at Khristianovich Institute of Theoretical and Applied Mechanics (ITAM). The results of these inlets test are compared with the data of numerical computations of inviscid, laminar, and turbulent flows carried out by the pseudo-unsteady method. There were determined the inlet throat areas limiting either with regard to the inlet starting or with regard to providing the maximally possible degree of geometric compression of the inlet-captured supersonic airstream at its deceleration in the already started inlet. Reshaping of computed flow patterns in the inlets depending on the variation of the minimal cross section of the inlet internal duct is analyzed.

Dynamic characteristics of a wind-tunnel ohmic heater

Dynamic characteristics of an ohmic heater intended for heating the working-gas flow in hot-shot wind tunnels have been experimentally studied. The experiments were performed on a specially designed test facility. Experimental data on the dynamic characteristics of the heater were obtained.

Effect of the mode composition disturbances in a high-enthalpy wind tunnel on wave processes in the hypersonic viscous shock layer

A numerical and experimental study of the spectral distribution of disturbances hotshot wind tunnel was performed. It was found that disturbances are the superposition of fast acoustic waves propagating along axial direction and oblique slow acoustic waves which have less amplitude. Numerical simulation of disturbances evolution in the nozzle of the wind tunnel was carried out by solving 2D Navier-Stokes equations using the ANSYS Fluent program package. Experiments were carried out in the IT-302M high-enthalpy hotshot wind tunnel ITAM SB RAS.

Burning carbon monoxide in the settling chamber of a hotshot wind tunnel for obtaining the CO2 test gas

A method of formation and heating of CO2 as a test gas in the settling chamber of a hotshot wind tunnel is considered. To form and heat CO2, the chamber is filled with a source gas mixture of CO, O2, and CO2, and after initiation, these substances participate in an exothermic chemical reaction in accordance with the formula CO + 0.5 O2 + xCO2 = (1 + x)CO2. A stoichiometric ratio of the concentrations of carbon monoxide CO and oxygen is used. Variation of the number of moles x of ballast CO2 in the left part of the chemical formula allows changing the temperature of the resultant test gas in a wide range. Experiments in the IT-302M hotshot wind tunnel carried out at ITAM SB RAS have shown that a pressure increase during an isochoric process in the settling chamber due to the joint effect of heat released in the reaction CO + 0.5 O2 and an electric charge provides the completeness of CO combustion almost equal to unity. The time of reaction completion at its initiation by an electric arc is no more than several milliseconds.

Slotted Channel As A Gasdynamical Source Of Ignition And Flame Stabilization In The Supersonic Combustion Chamber

The original scheme of flame stabilization in the channel at close to cocurrent fuel supply for the fuel combustion at a high supersonic speed has been designed. Such solution provides high temperature of a stream in a zone of fuel-air mixture formation. Computational and experimental investigations of self-ignition and combustion of hydrogen were carried out in the model of combustor chamber with slotted channel (gasdynamical source of ignition) at Mach numbers 3.7 and 5.8 at the entrance. Tests have been performed in hot-shot wind tunnel IT-302M of ITAM SB RAS in a mode of the attached pipe. Numerical study has been performed on the basis of solving the full averaged Navier-Stokes equations, supplemented k-Q SST turbulence model. Configuration of the slotted channel has been designed with two variants of exit nozzle: with and without geometrical throat. It has been established that at the channel entrance two vortexes with high temperature have been appeared. Temperature has been keeping high in the channel with geometrical throat and at blocking of the slotted channel without throat. It was found that uniform subsonic stream in the channel with geometrical throat has been realized. The stream in the slotted channel without geometrical throat keeps supersonic but Mach number was lower than in the main channel. The structure of the flow at the slotted channel exit is significantly differs for this both cases.

CONGRATULATIONS TO VOLF YAKOVLEVICH BOROVOY ON HIS 90TH BIRTHDAY!

July 18, 2014, marked the 90th birthday of Volf Yakovlevich Borovoy, Doctor of Technical Sciences, Professor, and Honored Researcher of the Russian Federation. Dr. Borovoy has been working at TsAGI since 1947, starting after he graduated from the Moscow Aviation Institute. His main areas of scientific interest are the aerodynamics of hypersonic flow and heat transfer, as well as methods of experimental research. He has published a monograph and over 150 scientific papers in journals worldwide and has obtained 15 inventor’s certificates. For many years Dr. Borovoy has initiated experimental studies on heat resistance materials for thermal protection of missiles and re-entry spacecraft. With his active participation, methods have been developed and implemented in practice that allow investigating heat transfer using temperature-sensitive coatings, measuring heat flux with surface thermocouple sensors, and visualizing spatial flow using laser sheets. With these methods, important features of three-dimensional separated flows have been found, including the generation of narrow peaks of intensified heat transfer, which are dangerous in flying vehicle structures. For these studies, Dr. Borovoy and his team of researchers were honored with the N. E. Zhukovsky Award in 1971 and the State Award of the Soviet Union in 1978. Volf Yakovlevich Borovoy has actively participated in the research of aerodynamic heating and thermal protection of the Buran shuttle and the Energia-Buran multiblock space transportation system. In the last 10 years he has initiated, and was the leader of, extensive scientific and experimental work on shock tubes. Through the initiative of Dr. Borovoy, new panoramic experimental methods of investigation have been successfully implemented, which have greatly enhanced the ability to glean information from experiments conducted in hot-shot wind tunnels. Dr. Borovoy and his coworkers were honored with the Government of the Russian Federation Award in 2008 for a series of studies on heat transfer on the surface of space vehicles entering the atmosphere of other planets. Because of his broad scientific vision and erudition, highest professionalism and self-discipline, and caring and respectful attitude toward colleagues, Volf Yakovlevich

High-enthalpy hot-shot wind tunnel with combined heating and stabilization of parameters

In the present paper, we consider instrumentation and the experimental procedure for conducting tests in a highenthalpy short-duration wind-tunnel facility, namely, a hypersonic hot-shot wind tunnel. We consider operation of the hot-shot wind tunnel with the test gas (TG) parameters kept constant during the regime and also operation of the tunnel as a traditional shock tube with a decay of the TG parameters that occurs as the TG leaves a constant-volume settling chamber. Stabilization of the TG parameters is achieved by using a pressure multiplier installed coaxially with the settling chamber, the configuration presenting a linear arrangement of the two components. Unloading of pressure multiplier dynamic component is achieved by using an equalizer whose piston moves in the opposite direction to the multiplier piston system. Several modes of wind tunnel operation with various combinations of different TG heating methods (electric arc, chemical energy, adiabatic compression, or heating in an external with respect to the settling chamber heat source) are possible. The design of a device responsible for diaphragm breakdown delay is considered. The design and dimensions of the wind tunnel provide for its normal operation under the following conditions: range of Mach numbers M = 4–20, range of settling-chamber temperatures Tch1 = 600–4000 K, and settling-chamber pressure pch1 up to 200 MPa (in operation with a double settling chamber, the stagnation pressure p0n = pch2 can be varied from 1 to 200 MPa). The settling chamber volume (80–100 dm3) is sufficiently large, allowing obtaining a 1-m diameter hypersonic stream in the test section during ∼ 100 ms (in combination with a second settling chamber).

Operation process and stabilization of kerosene combustion in a combustor model with high flow velocities at the combustor entrance

Results of an experimental study of the operation process in a model of an air-breathing combustor operating on heated kerosene with a supersonic air flow at the combustor entrance (Mach numbers 3 and 3.5) are presented. The tests are performed in a hotshot wind tunnel in the attached pipeline configuration with total temperatures of 2350–3250 K and pressures of 3.2–12.0 MPa. Data on ignition conditions and kerosene combustion efficiency are obtained. A principal possibility of using Ozawa’s criterion and its modification for the description of the range of stable combustion of the kerosene-air mixture in a combustor duct with flame holders shaped as cavities and steps in an essentially three-dimensional flow is demonstrated.

Ignition and combustion of hydrogen in a channel with high supersonic flow velocities at the channel entrance

Results of experimental investigations of a multi-injector combustion chamber in the attached pipeline regime are presented. An IT-302M hotshot wind tunnel based at the Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences is used as a source of a high-enthalpy gas (air). The tests are performed at Mach numbers of 3, 4, and 5 in the ranges of the total temperature from 2000 to 3000 K and static pressure from 0.08 to 0.23 MPa. The block of injectors is made in two variants: with different relative lengths of wedge-shaped injectors (cocurrent injection of hydrogen). The influence of the conditions at the combustor entrance on ignition and stable combustion of hydrogen is studied. Intense combustion of hydrogen is obtained only at Mach numbers of 3 and 4. The mechanism of the “two-stage” evolution of fuel combustion in the combustor is analyzed. The experimental data are analyzed and compared with numerical predictions.

Investigating an annular nozzle on combustion products of hydrocarbon fuels

Full-scale and computational experiments were used to investigate the flows in the jet thrust unit with annular nozzle and deflector in the form of a spherical segment. The used working gas was the combustion products of air mixtures with acetylene, gas-phase aviation kerosene, and natural gas. Experimental studies were carried out in a hot-shot wind tunnel in the range of stagnation pressure from 0.48 to 2.05 MPa. The calculations for the cases of combustion products outflow in terrestrial and high altitude conditions were performed with the original computer program that used the Euler and Navier-Stokes systems supplemented by equations of chemical kinetics. It was found that the thrust of the jet module with an annular nozzle at high altitude almost twice exceeds the sound nozzle thrust, but is lesser (about 25 %) than the thrust of the ideal calculated Laval nozzle; the difference therewith decreases markedly with the decrease of flight altitude and stagnation pressure.

Short-duration wind tunnel with combined heating and stabilization of parameters

A high-enthalpy short-duration wind tunnel (hotshot wind tunnel) is designed for different operation modes ensured by combining various methods of test gas heating [by an electric arc, chemical energy, adiabatic compression, and heating in an external source of heat (with respect to the settling chamber)]. The wind tunnel is designed for the following ranges of parameters: stagnation pressure p0 = 1–200 MPa, stagnation temperature T0 = 600–4000 K, Mach number M = 4–20, and test time t < 1 s. The wind tunnel can operate both in the regime of the classical hotshot facility with decreasing parameters of the test gas and in the regime with stabilization of parameters owing to synchronized motion of the opposite pistons of the pressure multiplier toward each other.

Experimental verification of the method of calculating the flow parameters in the test section of the hotshot wind tunnel

Calculated parameters of the gas flow in the test section of a high-enthalpy short-duration wind tunnel (IT-302M hotshot wind tunnel) are compared with experimentally determined values. It is demonstrated that the differences in flow characteristics in the test section measured by two methods [flow rate determined by the method of flask filling and physical velocity determined by particle image velocimetry (PIV)] and the calculated values is within several percent. The experimental results show that the assumptions taken for calculating the flow parameters in the test section ensure a fairly accurate description of the processes in the gas-dynamic duct of the hotshot wind tunnel. The most significant differences between the calculated and experimental values are found to be induced by two factors: neglect of heat losses from the test gas (gas flow) to the walls of the first settling chamber and uncertainty in reconstructing the pressure level in the first chamber at the time t = 0.

Composition of the test gas in the test section of a high-enthalpy wind tunnel

A method and system for sampling a chemically active gas from a hypersonic flow with high stagnation parameters are developed. Results of an experimental study of the test gas composition at the nozzle exit of the IT-302M hotshot wind tunnel based at the Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences are presented. As the air in the settling chamber is heated up to 3000 K by an electric arc only, the volume fraction of oxygen in the test section decreases from 21 to 18%, which may require supplying an additional amount of oxygen into the settling chamber as a compensation for its reduction in some tests of gas-dynamic models with combustion. In the case with hydrogen used together with the electric arc for increasing the energy of the facility, the degree of completeness of the reaction of hydrogen combustion in air in the settling chamber is determined. For the minimum possible supply of electric energy for the IT-302M wind tunnel (based on conditions of arc combustion stability), the hydrogen combustion efficiency is ≈0.9 for extremely lean hydrogen-air mixtures with the hydrogen concentration much lower than the flammability limits under standard conditions. The combustion efficiency rapidly approaches unity as the hydrogen concentration in the settling chamber and the electric energy supply are increased.