Reduction of the sonic boom level by heating the flow in front of the body

A numerical study of the possibility of reducing the sonic boom level in the case of local heat release to a supersonic gas flow at Mach number equal to 2 ahead of a body is described. The computations are performed for a spherical heat supply zone located on the flight trajectory ahead of the tip of an axisymmetric thin body. For the numerical study the combined method of “phantom bodies” is used. Different magnitudes of heat supply to the incoming flow are tested. These calculations are performed with allowance for interaction of shock waves emanating from the heated gas region and from the body in the far field. The computational results show that the local heat supply to a supersonic gas flow ahead of a body can reduce the sonic boom level by more than 20 %. The reduction of the sonic boom level is ensured by changing the free-stream parameters ahead of the body and by preventing the coalescence of shock waves from the heat supply zone and from the body in the far field.     

Controlling the level of the sonic boom generated by a flying vehicle by means of cryogenic forcing. 1. Cooling of the vehicle surface

The possibility of controlling the sonic boom level by means of cooling the surface of a flying vehicle is discussed. The effect of surface cooling on the formation of the perturbed flow structure at large distances from the vehicle is demonstrated by an example of a modified power-law body of revolution. The intensity of the intermediate shock wave and the perturbed pressure pulse near the body are seen to decrease, which expands the altitude range of the region where the sonic boom is reduced (down to 50%). At larger distances from the body, cryogenic forcing ensures a 12% decrease in the bow shock wave intensity. The possibility of controlling the process of formation of wave structures near the surface, such as barrel shock waves, is demonstrated. An explanation of the cryogenic forcing mechanism is offered. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 6, pp. 88–98, November–December, 2008.     

Controlling the level of the sonic boom generated by a flying vehicle by means of cryogenic forcing. 2. Distributed injection of a supercooled gas from the vehicle surface

The possibility of improving the efficiency of cryogenic forcing on the parameters of the hanging shock determining the length of the region of minimization of the sonic boom (middle zone) generated by a modified power-law body is studied. The effect of distributed injection of the coolant from the body surface on the formation of a perturbed flow near the body and at large distances from the body is considered. The scheme of distributed injection and the regime of coolant exhaustion are demonstrated to exert a significant effect on the length of the middle zone of the sonic boom. A scheme of cryogenic forcing is determined, which ensures reduction of bow shock wave intensity by more than 40% at distances corresponding to 7000 body diameters. The mechanism of cryogenic forcing on the flow structure near the body is discussed. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 2, pp. 136–144, March–April, 2009.     

基于混合网格的低声爆反设计方法研究

低声爆设计方法已成为新一代军民用超声速飞机研制过程中必须解决的关键难题之一。针对传统SGD低声爆外形反设计方法无法对声爆近场非线性效应进行描述和分析的缺点,提出了利用CFD方法求解得到的声爆近场压力分布代替F函数进行低声爆反设计的方法。声爆近场预测采用点-点对接的结构/非结构混合网格,充分利用非结构网格对复杂外形适应性强和结构化网格计算效率高的优点。结果分析表明,基于改进后的低声爆反设计方法得到的方案在声爆超压以及感觉噪声级等方面都比基于原始SGD方法得到的方案有较大改善。     

Shock unsteadiness creation and propagation: experimental analysis

The possibility of creating unsteady distortions of the tip shock by waves emitted from an aircraft is assessed experimentally. The model chosen is a cylindrical fore body equipped with a spike. This configuration is known for generating an important level of unsteadiness around the spike in supersonic regime. The wind tunnel Mach number is equal to 2. The experiments show that waves emitted from this source propagate along the tip shock and interact with it. It is then assessed that this interaction produces a periodic distortion of the shock that propagates to the external flow. Unsteady pressure sensors, high speed schlieren films, hot wire probing and laser Doppler velocimetry are used as complementary experimental means. The final result is a coherent representation of the complex mechanism of wave propagation that has been evidenced. The principle of creating unsteady shock deformation by onboard equipments could be examined as a possibly promising method of sonic boom control.     

Controlling the level of the sonic boom generated by a flying vehicle by means of cryogenic forcing. 3. Physical justification of the cryogenic action

The influence of the basic factors of cryogenic forcing on formation of the middle zone on the sonic boom and aerodynamic characteristics of the flying vehicle is studied by experimental and numerical methods. Experimental data obtained with alcohol or liquid nitrogen as an injected liquid are used for comparisons; as a result, the total effect of temperature and coolant evaporation can be determined. The influence of temperature is studied by means of numerical simulations of the cryogenic action of distributed injection of air. A comparison of numerical and experimental data reveals the effect of the coolant evaporation process on perturbed flow formation. It is demonstrated that evaporation of the coolant outgoing onto the vehicle surface should be intensified to increase the efficiency of cryogenic forcing (to decrease the coolant flow rate).     

Shape Sensitivity and Design for Fluids with Shocks

For many problems of compressible fluid dynamics it is desirable to find the sensitivity of the shock position with respect to the shape of the domain occupied by the fluid. One application is for the minimization of the sonic boom of airplanes; another is for the stability of the stream in fast-flowing rivers or canals. Classical calculus of variation is not valid for these cases because of the presence of Dirac functions appearing when a discontinuous function is differentiated, but we show here on the compressible potential flow equation how to find the equations of the derivatives and what are the linearized problems. Some numerical test cases are given for illustration.     

Thermal shielding of a sphere from the action of a strong shock wave

The time-dependent interaction of an incident shock wave with a sphere is considered in the presence of a heat supply region ahead of the body. The reflected shock configuration and the flow pattern are numerically investigated. The efficiencies of heat shields of different shapes are compared with respect to the longitudinal force acting on the sphere.     

Experimental investigation on tunnel sonic boom

Upon the entrance of a high-speed train into a relatively long train tunnel, compression waves are generated in front of the train. These compression waves subsequently coalesce into a weak shock wave so that a unpleasant sonic boom is emitted from the tunnel exit. In order to investigate the generation of the weak shock wave in train tunnels and the emission of the resulting sonic boom from the train tunnel exit and to search for methods for the reduction of these sonic booms, a 1300 scaled train tunnel simulator was constructed and simulation experiments were carried out using this facility.In the train tunnel simulator, an 18 mm dia. and 200 mm long plastic piston moves along a 40 mm dia. and 25 m long test section with speed ranging from 60 to 100 m/s. The tunnel simulator was tilted 8° to the floor so that the attenuation of the piston speed was not more than 10 % of its entrance speed. Pressure measurements along the tunnel simulator and holographic interferometric optical flow visualization of weak shock waves in the tunnel simulator clearly showed that compression waves, with propagation, coalesced into a weak shock wave. Although, for reduction of the sonic boom in prototype train tunnels, the installation of a hood at the entrance of the tunnels was known to be useful for their suppression, this effect was confirmed in the present experiment and found to be effective particularly for low piston speeds. The installation of a partially perforated wall at the exit of the tunnel simulator was found to smear pressure gradients at the shock. This effect is significant for higher piston speeds. Throughout the series of train tunnel simulator experiments, the combination of both the entrance hood and the perforated wall significantly reduces shock overpressures for piston speeds ofu _p ranging from 60 to 100 m/s. These experimental findings were then applied to a real train tunnel and good agreement was obtained between the tunnel simulator result and the real tunnel measurements.     

Two methods for calculating the load on the surface of a slender body executing axisymmetric vibrations in a sonic gas flow

Low-frequency axisymmetric vibrations of the surface of a slender body in a sonic flow are considered. The distribution of the stationary longitudinal velocity on the body is assumed to be linear. The linear equation with variable coefficients for the nonstationary part of the velocity potential is solved by two methods: by separation of the variables, as was done in [1] for a two-dimensional flow, and by the method of superposition of sources. Particular solutions with the required singularity are obtained.Translated from Izvestiya Akaderaii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 151–154, March–April, 1980.     

Multilevel functional preconditioning for shape optimisation

We study the application of a multi-level preconditioner to a practical optimal shape design problem. The preconditioner is based on the Bramble-Pasciak-Xu (BPX) series. We extend it to the unstructured parametrization of 3D shapes by using the volume–agglomeration heuristics. The choice of the smoothing parameter is analysed from functional arguments. Application to the shape design for optimising aerodynamic and sonic boom performances of a wing is demonstrated.     

Numerical analysis of the effect of local energy supply on the aerodynamic drag and heat transfer of a spherically blunted body in a supersonic air flow

The effect of local source of energy in a supersonic flow on the aerodynamic drag and heat transfer of a spherically blunted body is studied numerically. Calculations are performed on the basis of the Navier-Stokes equations for a thermally equilibrium model of air. Data on the effect of the intensity and size of the energy source on the wave drag, friction, and heat transfer are obtained. Particular attention is given to studying the effect of drag reduction by means of a focused heat source. The gas-dynamic nature of this effect is studied. The limits of drag reduction are estimated, and optimal conditions of heat supply are determined. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 5, pp. 171–179, September–October, 2000.     

Effect of Heat Supply on the Stability of the Supersonic Swept Atiachment-Line Boundary Layer

The stability of a boundary layer with volume heat supply on the attachment line of a swept wing is investigated within the framework of the linear theory at supersonic inviscid-free-stream Mach numbers. The results of numerical calculations of the flow stability and neutral curves are presented for the flow on the leading edge of a swept wing with a swept angle χ=60° at various free-stream Mach numbers. The effect of volume heat supply on the characteristics of boundary layer stability on the attachment line is studied at a surface temperature equal to the temperature of the external inviscid flow. It is shown that in the case of a supersonic external inviscid flow volume heat supply may result in an increase in the critical Reynolds number and stabilization of disturbances corresponding to large wave numbers. For certain energy supply parameters the situation is reversed, the unstable disturbances corresponding to the main flow-instability zone are stabilized but another zone of flow-instability with small wave numbers and a significantly lower critical Reynolds number appears.     

Reduction of Peak Heat Fluxes by Supplying Heat to the Free Stream

A supersonic flow past a blunt body in the presence of an incident oblique shock wave is considered. It is shown that by supplying heat to the free stream it is possible substantially to reduce local heat flux peaks on the body surface. The integral heat flux on the body surface increases by only a small fraction of the heat released into the flow.     

Heat and mass transfer at rotary heat exchangers in consideration of the condensation potential

In many industrial processes as well as in air conditioning systems heat and moisture is transferred by rotary heat exchangers from the warm exhaust air flow to the cold supply air flow. Rotary heat exchangers are classified as sorption rotors, hygroscopic rotors and condensation rotors. Basic mechanisms of heat and moisture transfer are presented. By means of the condensation potential as the difference between the moisture content of the warm air flow and the moisture content of the cold air flow at saturation the humidity transfer at the different rotor types is investigated. The condensation potential as a reference parameter provides the possibility to describe the influence of various air conditions in exhaust air and supply air flow on the humidity transfer of different rotary heat exchangers and to compare these rotors with each other. In order to give an overview of relevant design parameters, the influence of the speed of turning, the flute height of the rotor matrix and the velocity of the air flow regarding the heat and mass transfer is considered.     

Investigation of supersonic viscous flow past a sphere in the presence of subsonic and sonic injection

Supersonic flow past a sphere with a given rate of gas injection along the generator is investigated numerically on the range Re=10²–10⁴. Calculations have been made on the interval 0 90°, where is the angle between the axis of symmetry and the normal to the surface. It is shown that for high subsonic and sonic injection rates it is possible to observe qualitatively new features in the flow structure and in the distribution of the local supersonic flow characteristics around the perimeter of the sphere not previously noted in [9]. In the case of sonic injection the changes in flow structure occur only in the supersonic zone. In the neighborhood of the transition from a subsonic to sonic injection velocity the heat flux has a local maximum, which in absolute value does not exceed the heat flux in the absence of injection. It is shown that there may be qualitative differences in the pressure distribution over the surface of the body with increase in the injection parameter depending on the distribution and value of the injected gas flow rate and, moreover, the number Re.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 83–89, January–February, 1988.     

Separation of chemical elements in the discharge channel of an inductive plasma gun

Zones of separation of chemical elements in the air plasma flow in the discharge channel of the VGU-4 100-kW inductive plasma gun with a sonic nozzle of the Institute for Problems in Mechanics of the Russian Academy of Sciences are determined from an analysis of numerical solutions obtained within the framework of the Navier-Stokes equations. The occurrence of these zones and their possible influence on heat transfer to bodies in underexpanded jet flows in physical experiments are explained.     

Study on the equivalent convection coefficient of the hot surface of blast furnace stave

The calculation models of the equivalent convection coefficient between blast furnace gas flow and the hot surface of stave body, gas flow and in-laid brick were established by the combination of experiments and numerical calculation when the gas temperature is in the range of 505–1,248°C. The reason why the heat transfer coefficient between gas flow and in-laid brick is much more than that between gas and stave body was analyzed when the gas temperature is high. The opinion just to considering a kind of integration heat transfer coefficient while the numerical calculation of heat transfer model of stave will be changed. The division of above two heat transfer coefficients will increase the degree of heat transfer numerical calculation.     

Set-valued solutions for non-ideal detonation

The existence and structure of a steady-state gaseous detonation propagating in a packed bed of solid inert particles are analyzed in the one-dimensional approximation by taking into consideration frictional and heat losses between the gas and the particles. A new formulation of the governing equations is introduced that eliminates the difficulties with numerical integration across the sonic singularity in the reactive Euler equations. With the new algorithm, we find that when the sonic point disappears from the flow, there exists a one-parameter family of solutions parameterized by either pressure or temperature at the end of the reaction zone. These solutions (termed “set-valued” here) correspond to a continuous spectrum of the eigenvalue problem that determines the detonation velocity as a function of a loss factor.     

On the treatment of transient area variation in 1D discontinuous Galerkin simulations of train‐induced pressure waves in tunnels

To simulate the pressure wave generated by a train travelling through a tunnel, we implement a discontinuous Galerkin (DG) method for the solution of the one‐dimensional equations of variable area flow. This formulation uses a spatial discretisation via Legendre polynomials of arbitrary degree, and the resulting semi‐discrete system is integrated using an explicit Runge–Kutta scheme. A simulation of subsonic steady flow in a nozzle shows that the scheme produces stable solutions, without the need for artificial dissipation, and that its performance is optimal for polynomial degrees between 5 and 7. However, when dealing with an unsteady area, we report the presence of numerical oscillations that are not due to the steep pressure fronts in the flow but rather to the projection of a moving area, with piecewise continuous derivatives onto a fixed grid. We propose a reformulation of the DG method to eliminate these oscillations that, put in simple terms, amount to splitting the integrals where the derivatives of the cross‐sectional area are discontinuous into subintegrals where they are continuous. The resulting method does not exhibit oscillations, and it is applied here to two practical cases involving train‐induced pressure waves in a tunnel. The first application is a validation of the DG method through comparison of its computational results with pressure data measured during transit at the Patchway tunnel near Bristol (UK). The second application is a study of the influence of the nose shape and length on the pressure wave gradients responsible for sonic boom at tunnel exit portals to show that the proposed modification is able to deal with realistic train shapes. Copyright © 2012 John Wiley & Sons, Ltd.