Numerical investigation on properties of attack angle for an opposing jet thermal protection system

The three-dimensional Navier Stokes equation and the k-ε viscous model are used to simulate the attack angle characteristics of a hemisphere nose-tip with an opposing jet thermal protection system in supersonic flow conditions. The numerical method is validated by the relevant experiment. The flow field parameters, aerodynamic forces, and surface heat flux distributions for attack angles of 0°, 2°, 5°, 7°, and 10° are obtained. The detailed numerical results show that the cruise attack angle has a great influence on the flow field parameters, aerodynamic force, and surface heat flux distribution of the supersonic vehicle nose-tip with an opposing jet thermal protection system. When the attack angle reaches 10°, the heat flux on the windward generatrix is close to the maximal heat flux on the wall surface of the nose-tip without thermal protection system, thus the thermal protection has failed.

Investigation of thermal protection system by forward-facing cavity and opposing jet combinatorial configuration

This paper focuses on the usage of the forward-facing cavity and opposing jet combinatorial configuration as the thermal protection system （TPS） for hypersonic vehicles. A hemispherecone nose-tip with the combinatorial configuration is investigated numerically in hypersonic free stream. Some numerical results are validated by experiments. The flow field parameters, aerodynamic force and surface heat flux distribution are obtained. The influence of the opposing jet stagnation pressure on cooling efficiency of the combinatorial TPS is discussed. The detailed numerical results show that the aerodynamic heating is reduced remarkably by the combinatorial system. The recirculation region plays a pivotal role for the reduction of heat flux. The larger the stagnation pressure of opposing jet is, the more the heating reduction is. This kind of combinatorial system is suitable to be the TPS for the high-speed vehicles which need long-range and long time flight.

Thermal Protection Efficiency of Forward-facing Cavity and Opposing Jet Combinational Configuration

To deal with the thermal protection of high speed vehicle, the cooling efficiency of a combinatorial thermal protection configuration which is composed of the forward-facing cavity and opposing jet is investigated. The numerical simulation result is validated by experiment and the flow field parameters, aerodynamic force and heat flux distribution are obtained. The detailed numerical simulation results show that this kind of combinatorial thermal protection configuration has an excellent effect on cooling the surface of the nosetip. By adding of the opposing jet with a small total pressure, it can avoid the disadvantage to the control performance of the aircraft which is caused by the cavity oscillating flow. And the low stagnation pressure is propitious to simplify the opposing jet system. The location of the recirculation region has a significant impact of the aerodynamic heating. The heat flux along outer body surface of the nosetip does not increase with the stagnation pressure of opposing jet decreases monotonically.

A New Method of Thermal Protection by Opposing Jet for a Hypersonic Aeroheating Strut

This paper presents the numerical investigation of thermal protection of scramjet strut by opposing jet in supersonic stream of Mach number 6 with a hydrogen fueled scramjet strut model using CFD software. Simulation results indicate that when a small amount of fuel is injected from the nose of the strut, the bow shock is pushed away from the strut, and the heat flux is reduced in the strut, especially at the leading edge. Opposing jet forms a recirculation region near the nozzle so that the strut is covered with low temperature fuel and separated from free stream. An appropriate total pressure ratio can be used to reduce not only aerodynamic heating but also the drag of strut. It is therefore concluded that thermal protection of scramjet strut by opposing jet is one of the promising ways to protect scramjet strut in high enthalpy stream.

Influence of angle of attack on a combined opposing jet and platelet transpiration cooling blunt nose in hypersonic vehicle

Flying condition with angle of attack is inevitable in a hypersonic vehicle,and it may influence the thermal protection system(TPS)performance of opposing jet and its combinations.A 3D Navier–Stokes equation and shear stress transfer(SST)k-ωmodel with compressible correction are employed to simulate the angle of attack characteristics of a blunt body with opposing jet and platelet transpiration TPS.The flowfield and heat flux transfer for angles of attack 0°,3°,6°with jet pressure ratio PR=0.1 and 0°,6°,12°with PR=0.2 are obtained.Numerical results show that the flowfield is no longer symmetrical with the effect of the angle of attack.The flowfield and heat transfer in windward and leeward performed adversely.The recompression shock wave in windward is strengthened,which increases local temperature and strengthens heat transfer.The opposing jet fails in thermal protection when the angle of attack reaches critical value;however,the critical angle of attack can be promoted by increasing PR.Finally,the transpiration gas can strengthen the cooling efficiency of windward,thereby,increasing the critical angle of attack.

Effect of CO_(2) Opposing Multiple Jets on Thermoacoustic Instability and NO_(x) Emissions in a Lean-Premixed Model Combustor

This paper experimentally studied the effect of CO_(2) opposing multiple jets on the thermoacoustic instability and NO_(x) emissions in a lean-premixed model combustor.The feasibility was verified from three variables:the CO_(2) jet flow rate,hole numbers,and hole diameters of the nozzles.Results indicate that the control effect of thermoacoustic instability and NO_x emissions show a reverse trend with the increase of open area ratio on the whole,and the optimal jet flow rate range is 1-4 L/min with CO_(2) opposing multiple jets.In this flow rate range,the amplitude and frequency of the dynamic pressure and heat release signals CH~* basically decrease as the CO_(2) flow rate increases,which avoids high-frequency and high-amplitude thermoacoustic instability.The amplitude-damped ratio of dynamic pressure and CH*can reach as high as 98.75% and 93.64% with an optimal open area ratio of 3.72%.NO_(x) emissions also decrease as the jet flow rate increases,and the maximum suppression ratio can reach 68.14%.Besides,the flame shape changes from a steep inverted "V" to a more flat "M",and the flame length will become shorter with CO_(2) opposing multiple jets.This research achieved the synchronous control of thermoacoustic instability and NO_(x) emissions,which could be a design reference for constructing a safer and cleaner combustor.

Experimental and numerical investigation on opposing plasma synthetic jet for drag reduction

Experimental and numerical studies are carried out to validate the potential of opposing Plasma Synthetic Jet(PSJ)for drag reduction for a hemisphere.Firstly,flow field changes of opposing PSJ are analyzed by comparing the experimental schlieren images and simulation results in a supersonic free stream of Mach number 3.As PSJ is a kind of unsteady pulsed jet,the shock standoff distance increases initially and then decreases under the control of PSJ,which corresponds to the change of the strength of PSJ.Accordingly,the amount of drag reduction of the hemisphere increases initially and then decreases.It is found that there is a short period of“drag rise”during the formation of PSJ before the drag reduction,which is induced by the generation of normal shock waves and the area difference of the cavity wall of PSJ Actuator(PSJA).Secondly,the effects of five parameters,including exit diameter,discharge energy of PSJA,Mach number,static pressure of incoming flow and angle of attack,on drag reduction of opposing PSJ were studied in detail by using numerical method.It is found that the Maximum Pressure Ratio(MPR)has a significant impact on the average drag reduction for a configuration-determined PSJA.For the configuration selected in this study,the flow field of opposing PSJ shows typical Short Penetration Mode(SPM)in a control cycle of PSJ when the MPR is less than 0.89.However,the flow field shows typical Long Penetration Mode(LPM)at some time when the MPR is bigger than 0.89.Relatively better drag reduction is achieved in this case.

Assessing stress conditions and impact velocities in fluidized bed opposed jet mills

Fluidized bed opposed jet mills are capable of meeting the continuously growing dema nd for contamination-free fine particles.In this type of jet mill,the solid material is entrained and accelerated by expanding gas jets that are focused onto a focal point in side a fluidized bed.The resulting particle collisions induce breakage.The process is affected by the relative particle velocities and the number of particle-particle collisions.Clearly,both quantities are distributed.However,to date,neither relative particle velocities nor collision frequencies in such units have been determined.The present work introduces an innovative method to assess the stressing conditions in jet mills experimentally.To this end,mixtures of glass and ductile metal microspheres were used,with the latter employed in small amounts.Inter-particle collisions between the aluminum and glass spheres lead to the formation of dents on the microparticles.The size and number of these dents are associated with the individual collision velocities and overall collision frequencies.The correlation between dent size and collision velocity was obtained from finite element calculations based on empirical data.The proposed approach was validated using particle image velocimetry during secondary gas injection into a fluidized bed reactor.In this case the effect of the distance between two opposed nozzles was examined.For a lab-scaled fluidized bed opposed jet mill the effects of gas pressure and hold-up were investigated.Relative particle velocities were found to be sign ificantly lower tha n the gas velocities,while the nu mber of contacts per particle was determined to be extremely high.

Analysis of Cold Flowfield of Multi-Annular Opposed Jets

The technique of the use of multi-annular opposed jets as different from using swirl and bluff body creates an excellent recirculation zone with desired size in a large space.The size of recirculation,the magnitude of reverse velocity and turbulence intensity are much greater than those formed by bluff body.Factors affecting the flowfield include the velocity ratio of the opposed jets to the primary air J,the diameter and construction of the opposed jet ring,secondary air velocity and configuration,and confined or unconfined flow condition and so on.This method is a promising way for flame stabilization in combustion technology.