Experimental study on shock interaction control of double wedge in high-enthalpy hypersonic flow subject to plasma synthetic jet

The hypersonic shock-shock interaction flow field at double-wedge geometries controlled by plasma synthetic jet actuator is experimentally studied in a Ma = 8 high-enthalpy shock tunnel with the purpose of exploring a novel technique for reducing surface heat flux in a real flight environment. The results demonstrate that increasing the discharge energy is advantageous in eliminating the shock wave, shifting the shock wave interaction point, and shortening the control response time. The oblique shock wave can be completely removed when the actuator's discharge energy grows from 0.4 J to 11.5 J, and the displacement of the shock wave interaction point increases by 124.56%, while the controlled response time is shortened by 30 μs. Besides, the reduction in diameter of the jet exit is firstly proved to have a negative impact on energy deposition in a working environment with incoming flow, which reduces the discharge energy and hence decreases the control effect. The shock wave control response time lengthens when the jet exits away from the second wedge. Along with comparing the change in wall heat flux at the second wedge over time, the control effect of plasma synthetic jet actuator with and without inflation is also analyzed. When plasma synthetic jet works in inflatable mode, both the ability to eliminate shock waves and the shifting effect of the shock wave interaction point are increased significantly, and the wall heat flux is also reduced.

Advances in critical technologies for hypersonic and high-enthalpy wind tunnel

Hypersonic and high-enthalpy wind tunnels and their measurement techniques are the cornerstone of the hypersonic flight era that is a dream for human beings to fly faster,higher and further.The great progress has been achieved during the recent years and their critical technologies are still in an urgent need for further development.There are at least four kinds of hypersonic and high-enthalpy wind tunnels that are widely applied over the world and can be classified according to their operation modes.These wind tunnels are named as air-directly-heated hypersonic wind tunnel,light-gas-heated shock tunnel,free-piston-driven shock tunnel and detonation-driven shock tunnel,respectively.The critical technologies for developing the wind tunnels are introduced in this paper,and their merits and weakness are discussed based on wind tunnel performance evaluation.Measurement techniques especially developed for high-enthalpy flows are a part of the hypersonic wind tunnel technology because the flow is a chemically reacting gas motion and its diagnosis needs specially designed instruments.Three kinds of the measurement techniques considered to be of primary importance are introduced here,including the heat flux sensor,the aerodynamic balance,and optical diagnosis techniques.The techniques are developed usually for conventional wind tunnels,but further improved for hypersonic and high-enthalpy tunnels.The hypersonic ground test facilities have provided us with most of valuable experimental data on high-enthalpy flows and will play a more important role in hypersonic research area in the future.Therefore,several prospects for developing hypersonic and high-enthalpy wind tunnels are presented from our point of view.

Oblique-mode breakdown in hypersonic and high-enthalpy boundary layers over a blunt cone

The nonlinear analyses of the hypersonic and high-enthalpy boundary-layer transition had received little attention compared with the widely-studied linear instabilities.In this work,the oblique-mode breakdown,as one of the most available transition mechanisms,is studied using the nonlinear parabolized stability equations(NPSE)with consideration of the thermal-chemical non-equilibrium effects.The flow over a blunt cone is computed at a free-stream Mach-number of 15.The rope-like structures and the spontaneous radiation of sound waves are observed in the schlieren-like picture.It is also illustrated that the disturbances of the species mass and vibrational temperature near the wall are mainly generated by the product term of the wall-normal velocity disturbance and the mean-flow gradient.In comparison to the CPG flow,the TCNE effects destabilize the second mode and push upstream the N factor envelope.The higher growth rate of the oblique wave leads to stronger growth of the streamwise vortices and harmonic waves.

Theories and methods for designing hypersonic high-enthalpy flow nozzles

Hypersonic high-enthalpy wind tunnels have been a challenge to ground tests in aerospace research area for decades and its test flow uniformity is one of the most important parameters for evaluating wind tunnel performances.Regarding to the performance requirement,theories and methods for designing hypersonic flow nozzles at high enthalpy conditions are quite difficult,but very interesting topics,especially when air molecule dissociations take place in wind tunnel test gas reservoirs.In this paper,fundamental theories and important methods for nozzle designs are briefly reviewed with the emphasis on two-dimensional axisymmetric nozzles for hypersonic high-enthalpy wind tunnels,including the Method of Characteristics(MOC),the graphic design method,the Sivells method,the theory for boundary correction,and the CFD-based design optimization methods.These theories and methods had been proposed based on several physical issues,respectively,which play important roles in nozzle flow expansion processes.These issues cover the expansion wave generation and reflection,the boundary layer development,the real gas effect of hypersonic high-enthalpy flows.Difficulties arising from applications of these methods in hypersonic high-enthalpy nozzle design are discussed in detail and the state of the art of the nozzle design technologies that have reached for decades is summarized with some brief comments.Finally,the prospect for the hypersonic nozzle design methods,and its numerical and experimental verifications are provided with from authors’viewpoint for readers’reference.

Estimation of the Ballistic Effectiveness of 3,4-and 3,5-Dinitro-1-(trinitromethyl)-1H-Pyrazoles as Oxidizers for Composite Solid Propellants

The experimental values of the enthalpy of formation of two isomeric 3,4-and 3,5-dinitro-1-(trinitromethyl)-1H-pyrazoles have been obtained(261.5±5.0and 246.4±6.7kJ/mol for crystalline 3,4-and 3,5-dinitro-1-(trinitromethyl)-1H-pyrazoles,respectively).The ballistic effectiveness of these potential oxidizers in composite solid propellants was studied.It is shown that these two oxidizers may be successfully applied in metal-free compositions or with a small content of metal.For the bottom stage 3,4-dinitro-1-(trinitromethyl)-1H-pyrazole is a bit better than 3,5-dinitro-1-(trinitromethyl)-1H-pyrazole,for the upper stage the both oxidizers show the equal ballistic parameters.These oxidizers allow to create metal-free solid composite propellants with the binder percentage not lower than 19%(volume fraction),with I3spequal to 256.5-257.0sat density equal to 1.72-1.74g/cm^3.

Dependence of Specific Impulse of Metal-free Formulations on CHNO-oxidizer′s Element Content and Enthalpy of Formation

It is shown that it is not correct to estimate energetic characteristics of different compounds of solid composite propellants by evaluation of the specific impulse values of these components serving as an only component in the formulation.Such an approach may turn the researcher to a wrong conclusion.One has to compare compound′s potential in formulations close to real,e.g.at least with necessary amount of binders.Dependences of specific impulse upon element content of highenthalpy CHNO oxidizer,its enthalpy of formation,and kind of binder have been found.

Investigation of dual ignition for a detonation-driven shock tunnel in forward driving mode

A detonation-driven shock tunnel is useful as a ground test facility for hypersonic flow research.The forward detonation driving mode is usually used to achieve high-enthalpy flows due to its strong driving capability.Unfortunately,the strong detonation wave front results in diaphragm fragments that disturb the test flow and scratch the nozzle or test models.In this study,a dual ignition system was developed to burst a metal diaphragm without fragmentation in the forward driving mode.A series of experiments were conducted to validate the proposed technique.The influences of the delay time setting on the test conditions were investigated in detail.Numerical simulations were also conducted to obtain a better understanding of the wave processes in the shock tube.The results showed that the dual ignition system solved the diaphragm issues in the forward driving mode.The test time was shortened due to the additional ignition close to the primary diaphragm;the smaller the delay time,the shorter the effective test time.However,a small amount of time loss is considered worthwhile because the severe diaphragm problems have been solved.