Body In Hypersonic Flow Research Articles

Characterization of Disturbance Resonance in Postshock of Blunt Body in Hypersonic Flow

A pitot probe is commonly used for the disturbance quantification of a hypersonic freestream, but the pitot results cannot reflect the actual disturbance amplitudes due to the turbulence/shock-wave interactions as well as the disturbance resonances. In this work, we characterize the disturbance resonance in the postshock zone of a blunt body using both experimental and theoretical approaches. A one-dimensional interference model with four traveling sound waves is proposed to simulate the resonance phenomenon due to the reflection between the detached shock and the wall of the pitot probe. Subsequently, the total pressure fluctuation on the surface and the density fluctuation in the space along the centerline are investigated using a pressure sensor and a noninvasive focused laser differential interferometer. Both the experimental results and theoretical analysis show the resonance mechanism on the surface is dominated by the interference between the initial diverging sound wave and the shock-reflected sound wave. In contrast, the stationary wave formed by the initial diverging sound wave and the body-reflected wave plays a leading role in the space. Finally, an equation is proposed to approximate the destructive resonant frequency in the space.

On two-dimensional steady hypersonic-limit Euler flows passing ramps and radon measure solutions of compressible Euler equations

We proposed rigorous definitions of Radon measure solutions for boundary value problems of steady compressible Euler equations which modeling hypersonic-limit inviscid flows passing two-dimensional ramps, and their interactions with still gas and pressureless jets. We proved the Newton-Busemann pressure law of drags of body in hypersonic flow, and constructed various physically interesting measure solutions with density containing Dirac measures supported on curves, also exhibited examples of blow up of certain measure solutions. This established a mathematical foundation for applications in engineering and further studies of measure solutions of compressible Euler equations.

Observation of unsteady motion induced by counterflow jet on blunt body in hypersonic flow

Observation of unsteady motion induced by counterflow jet on blunt body in hypersonic flow

Aerodynamics of inclined cylindrical bodies free-flying in a hypersonic flowfield

The influence of the flight attitude on aerodynamic coefficients and static stability of cylindrical bodies in hypersonic flows is of interest in understanding the re/entry of space debris, meteoroid fragments, launch-vehicle stages and other rotating objects. Experiments were therefore carried out in the hypersonic wind tunnel H2K at the German Aerospace Center (DLR) in Cologne. A free-flight technique was employed in H2K, which enables a continuous rotation of the cylinder without any sting interferences in a broad angular range from 0^{circ } to 90^{circ }. A high-speed stereo-tracking technique measured the model motion during free-flight and high-speed schlieren provided documentation of the flow topology. Aerodynamic coefficients were determined in careful post-processing, based on the measured 6-degrees-of-freedom (6DoF) motion data. Numerical simulations by NASA’s flow solvers Cart3D and US3D were performed for comparison purposes. As a result, the experimental and numerical data show a good agreement. The inclination of the cylinder strongly effects both the flowfield and aerodynamic loads. Experiments and simulations with concave cylinders showed marked difference in aerodynamic behavior due to the presence of a shock–shock interaction (SSI) near the middle of the model.Graphic abstract

Experimental study of separation behavior of two bodies in hypersonic flow

The separation behavior of two bodies was experimentally investigated in a shock tunnel. Simple-shaped bodies, including a cylinder, cube, and sphere, with a size of 3 or 5 mm were used as the test models. The two contact models with a plane-exposed configuration were mounted using a thin wire, and the separation behavior was observed and analyzed using the shadowgraph technique. The surface roughness effect on the separation of two spheres was also considered. Particularly, attention was given to the lateral velocity. It was found that the spheres had a constant final lateral velocity after the shock interaction, whereas the velocities of the cylinders and cubes were determined by the rotational motion of the body. Based on the experimental data, a reentry trajectory analysis was conducted using Monte Carlo simulation. The results showed large ground footprint and downrange differences depending on the characteristics of the body, implying the importance of separation behavior for a reentry analysis.

Aerothermal prediction of hypersonic flow around spherical capsule model using IDDES approach

The prediction of heat transfer for blunt bodies in hypersonic flows remains a great challenge. In particular, the uncertainties are larger in the leeside due to the complexity of the wake flow. Generally, the heat transfer is over-predicted using the Reynolds-averaged Navier–Stokes (RANS) models. In this paper, the improved delayed detached eddy simulation (IDDES) method is used to simulate the Mach 6 flow around a scaled spherical capsule model. In addition, a low dissipative WENO scheme is used for inviscid fluxes and dual-time stepping method is applied for time advancement. Results are compared to experimental data for mean and instantaneous heat transfer in the leeside of the aftbody. It is shown that the integrated error is 75.49% for RANS while 35.69% for IDDES method. Moreover, the multi-scale structures in the separation region are also resolved well by the IDDES method.

Radon measure solutions for steady compressible Euler equations of hypersonic-limit conical flows and Newton's sine-squared law

We formulate a mathematical problem on hypersonic-limit of three-dimensional steady uniform non-isentropic compressible Euler flows of polytropic gases passing a straight cone with arbitrary cross-section and attacking angle, which is to study Radon measure solutions of a nonlinear hyperbolic system of conservation laws on the unit 2-sphere. The construction of a measure solution with density containing Dirac measures supported on the surface of the cone is reduced to find a regular periodic solution of highly nonlinear and singular ordinary differential equations (ODE). For a circular cone with zero attacking angle, we then proved the Newton's sine-squared law by obtaining such a measure solution. This provides a mathematical foundation for the Newton's theory of pressure distribution on three-dimensional bodies in hypersonic flows.

Numerical investigation of the effect of disk position on the aerodynamic heating and drag of a spiked blunt body in hypersonic flow

ABSTRACTDetailed numerical simulations have been carried out on a spiked blunt body with multiple hemispherical disks using a commercial CFD code in order to investigate their effectiveness in reducing the aerodynamic drag and heating. The base configuration is a hemispherical cylinder whose diameter is 40 mm with an overall length of 70 mm. The lengths of the aerospikes investigated are 1, 1.5, 2 and 2.5 times the base diameter of the cylinder and the radii of the aerodisks are varied between 0.05, 0.1, 0.15 and 0.2 times the diameter of the cylinder. Besides these, the position of the aerodisks is varied with the rearmost aerodisk placed at 25%, 50% and 75% along the length of the aerospike and the intermediate aerodisk for three-disk cases, positioned at 25%, 50% and 75% of the distance between the front and the rearmost disk. All the investigations have carried out at a freestream Mach number of 6.2 and Reynolds number of 2.64 × 107/m. It has been observed that the multidisk spikes are advantageous for the purpose of reduction of both aerodynamic drag and heating at hypersonic speed. The two aerodisk spiked configurations show better results in terms of aerodynamic heating and drag in comparison to the single-disk aerospikes while the three-disk spikes yield only a marginal reduction in aerodynamic drag over the two-disk configurations. For reduction of heat fluxes and heat transfer rates though, the three-disk configurations are extremely advantageous and give much larger reductions are compared to the two-disk configurations.

Numerical Studies On Effect Of Changing Mach Number On Aero Disk Model On Flow Contours And Drag Force

A supersonic aircraft needs to travel in the atmosphere at different Mach numbers. In this paper the effect of Mach number on a body in hypersonic flow is studied. Also the effect of scaling on the flow behaviour is studied. As the original geometry taking more computational time, scaled model is used for further research. The geometry is modelled, meshed and solved in Ansys tool. Results are compared with available literature and further parametric study is done. There was no appreciable change found in the results obtained by scaled model compared with actual model. Hence Actual body[1] was scaled to 1/10th of its original scale body and simulated at different Mach numbers. The spike of the cone is fitted with an aero disk. Results shows that the angle of the bow shock inclined to body is found to be decreasing as the Mach number is increasing. Two separate shockwaves from disc and cone were found merged at higher Mach numbers. At starting Mach numbers the separation region was unaltered but after Mach number 3, Mach number contours show that flow deflected from aero disk has greater role in deciding the separation region ahead of cone. Further surface pressure graphs are plotted and effect on drag force were discussed.

Hypersonic Blunt-Body Shape Optimization for Reducing Drag and Heat Transfer

A large design concern for high-speed vehicles such as next-generation launch vehicles or reusable spacecraft is the drag and heat transfer experienced at hypersonic velocities. In this paper, the optimized shapes for both minimum drag and minimum peak heat flux for an axisymmetric blunt body are developed using computational-fluid-dynamics software in conjunction with a genetic algorithm. For flowfield calculations, the commercial flow solver ANSYS Fluent is employed to solve the unsteady compressible Reynolds-averaged Navier–Stokes equations in conjunction with the shear-stress transport turbulence model. The hypersonic body shape is optimized using a multi-objective genetic algorithm to minimize both the drag and heat transfer. The multi-objective genetic algorithm creates a Pareto-optimal front containing the optimized shapes for various relative objectives of minimized drag and heat transfer. The results show a significant decrease in both the drag and peak heat flux and exhibit the expected changes in the body profile. It should be noted that shape optimizations of a blunt body in hypersonic flow for reducing both drag and heat flux through use of a multi-objective genetic algorithm are reported in this paper for the first time in the literature. The proposed methodology will allow the simulation and optimization of more complex shapes of hypersonic vehicles.

An expression for the dynamic stability of blunt slender elliptic bodies in hypersonic flow

AbstractDynamic stability data on axially symmetric pointed and blunt cones, parabolic profiles and other ogive and blunt cylindrical shapes is readily available in literature; the dynamic stability on elliptic blunt paraboloids has not been studied at any great lengths in the past. Both numerical and experimental results are scarce. The present paper uses the shock expansion method to obtain the unsteady pressure distribution on blunt elliptic conical bodies at small angles-of-attack. The resulting unsteady pressure distribution is suitably integrated over the surface of the elliptic body to obtain appropriate analytic expressions for static and dynamic stability. Owing to scarcity of meaningful numerical or measured data for elliptic bodies, the results are compared in qualitative terms against published dynamic stability data on pointed elliptical cones or other axisymmetric blunt cones.

Experimental study on supersonic film cooling on the surface of a blunt body in hypersonic flow

The experimental study focuses on the heat flux on a double cone blunt body in the presence of tangential-slot supersonic injection into hypersonic flow. The tests are conducted in a contoured axisymmetric nozzle with Mach numbers of 7.3 and 8.1, and the total temperature is about 900 K. The injection Mach number is 3.2, and total temperature is 300 K. A constant voltage circuit is developed to supply the temperature detectors instead of the normally used constant current circuit. The schlieren photographs are presented additionally to visualize the flow and help analyze the pressure relationship between the cooling flow and the main flow. The dependence of the film-cooling effectiveness on flow parameters, i.e. the blow ratio, the convective Mach number, and the attack angle, is determined. A semi-empirical formula is tested by the present data, and is improved for a better correlation.

Flow Structures and Heating Augmentation Around Finite-Width Cavity in Hypersonic Flow

Cavities significantly affect the heating of bodies in hypersonic flows. Previous studies have shown that boundary-layer flows can enter the interior of shallow cavities and augment heating. In this study, the three-dimensional flow structure induced by a finite-width rectangular cavity was revealed in compressible Navier–Stokes simulations. A finite-width rectangular cavity was found to encourage downwash into the cavity, and a pair of counter-rotating longitudinal vortices was established in the wake region of the cavity. The downwash draws high-speed boundary-layer flow into the cavity and augments the heating on the cavity floor. The high-speed flow impinges on the cavity endwall and causes local peak heating. Slowly dissipating longitudinal vortices are produced that generate long streaky hot regions in the wake. The heating augmentation induced by deep or narrow cavities is less than in shallow and wide cavities owing to the insignificant amount of high-speed flow entering the cavity.

Interaction of Laser Energy with Bow Shock in Mach 5 Flow

In order to develop a potential way to reduce the stagnation pressure and heat flux of the blunt body in hypersonic flow, single pulsed and high rated laser energy are deposited respectively to control the bow shock in Mach 5 flow. Process of the interaction of 100mJ single pulsed laser energy with bow shock is studied by schlieren experiment in Mach 5 shock tunnel. The results indicate that the schlieren photographs and stagnation pressure at different times fit well with the simulation. Bow shock is distorted by the laser induced blast wave. During a single laser pulse, the average stagnation pressure and temperature are reduced by 6.5% and 3.4%. High rated laser energy is used to sustain the low pressure and heat flux region to increase the control efficiency. With the power of 6.6% of the enthalpy flux, when the distance of deposition point and blunt body is 1.1 times of the diameter of the blunt body, the pressure and heat flux of the stagnation point is reduced to 49% and 75%, respectively. The mechanism of interaction of laser and bow shock is disclosed.

Numerical Study of Film Cooling Scheme on a Blunt-Nosed Body in Hypersonic Flow

In hypersonic flight, the prediction of aerodynamic heating and the construction of a proper thermal protection system (TPS) are significantly important. In this study, the method of a film cooling technique, which is already the state of the art in cooling of gas turbine engines, is proposed for a fully reusable and active TPS. Effectiveness of the film cooling scheme to reduce convective heating rates for a blunt-nosed spacecraft flying at Mach number 6.56 and 40 deg angle of attack is investigated numerically. The inflow boundary conditions used the standard values at an altitude of 30 km. The computational domain consists of infinite rows of film cooling holes on the bottom of a blunt-nosed slab. Laminar and several turbulent calculations have been performed and compared. The influence of blowing ratios on the film cooling effectiveness is investigated. The results exhibit that the film cooling technique could be an effective method for an active cooling of blunt-nosed bodies in hypersonic flows.

Transition Experiments on Blunt Bodies with Isolated Roughness Elements in Hypersonic Flight

Smooth titanium hemispheres with isolated three-dimensional (3D) surface roughness elements were flown in the NASA Ames hypersonic ballistic range through quiescent CO2 and air environments. Global surface intensity (temperature) distributions were optically measured and thermal wakes behind individual roughness elements were analyzed to define tripping effectiveness. Real-gas Navier-Stokes calculations of model flowfields, including laminar boundary layer development in these flowfields, were conducted predict key dimensionless parameters used to correlate transition on blunt bodies in hypersonic flow. For isolated roughness elements totally immersed within the laminar boundary layer, critical roughness Reynolds numbers for flights in air were found to be higher than those measured for flights in CO2, i.e., it was easier to trip the CO2 boundary layer to turbulence. Tripping effectiveness was found to be dependent on trip location within the subsonic region of the blunt body flowfield, with effective tripping being most difficult to achieve for elements positioned closest to the stagnation point. Direct comparisons of critical roughness Reynolds numbers for 3D isolated versus 3D distributed roughness elements for flights in air showed that distributed roughness patterns were significantly more effective at tripping the blunt body laminar boundary layer to turbulence.

A Perturbation Method to Analyze the Effect of Cross Section and Angle of Attack for Some Conical Bodies in Hypersonic Flow

An analysis is performed to study the supersonic flow over conical bodies of three different cross sections circular, elliptic and squircle (square with rounded corners) shaped. Perturbation method is applied to find flow variables analytically. In order to find lift and drag forces the pressure force on the body is found, the component along x is drag and the component along z is lift. Three equations are obtained for lift to drag ratio of each cross section. The graphs for L/D show that for a particular cross section an increase in angle of attack, increases L/D. Comparing L/D in the three mentioned cross sections it is obtained that L/D is the greatest in squircle then in ellipse and the least in circle. The results have applications in design of flying objects such as airplanes where many more seats can be arranged in ellipse and or squircle cross section compared to regular circular case.

0604 極超音速流中のエアロスパイク付き鈍頭物体の表面熱流束における3次元効果(OS6-1 超音速流と衝撃波,オーガナイズドセッション)

A blunt body in hypersonic flow is subjected to severe aerodynamic heating and drag. This is one of the most critical problems of designing the hypersonic vehicles such as Reusable Launch Vehicles(RLV). It is well known that the spiked-nose(aerospike)concept is effective to reduce aerodynamic drag on asymmetric blunt bodies in hypersonic flow. In this study, we investigated the heat flux distribution on a blunt-nosed body with an aerospike in hypersonic flow. The flow field around a blunt-nosed body is calculated by the full Navier-Stokes simulations to compare with the experimental data such as Schlieren photographs and TSP(Temperature Sensitive Paint)images. It was found that the heat flux distributions changes widely with the angle of attack. Moreover, the correlation between heat flux and the flow and the flow field exists due to the shock/shock interaction patterns for various angle-of-attacks.

Numerical study of interference between simple-shape bodies in hypersonic flows

Hypersonic rarefied-gas flows near two side-by-side plates and cylinders, toroidal balloon, plate and cylinder over a plane surface, and plate behind a cylinder in argon, nitrogen, oxygen, and carbon dioxide have been studied numerically using the direct simulation Monte-Carlo technique under the transition flow conditions at Knudsen numbers from 0.004 to 10. Strong influences of the geometrical factor (the ratio of a distance between bodies to a body length) and the Knudsen number on the flow structure about the bodies (shock-wave shapes, the configuration of subsonic flow zones), skin friction, pressure distribution, lift, and drag have been found.

Experimental investigation on spiked body in hypersonic flow

AbstractA spike attached to a hemispherical body drastically changes its flowfield and influences aerodynamic drag in a hypersonic flow. It is, therefore, a potential candidate for drag reduction of a future high-speed vehicle. The effect of the spike length, shape, spike nose configuration and angle-of-attack on the reduction of the drag is experimentally studied with use of hypersonic wind-tunnel at Mach 6. The effects of geometrical parameters of the spike and angle-of-attack on the aerodynamic coefficient are analysed using schlieren picture and measuring aerodynamic forces. These experiments show that the aerodisk is superior to the aerospike. The aerodisk of appropriate length, diameter and nose configuration may have the capability for the drag reduction. The inclusion of an aero disk at the leading edge of the spike has an advantage for the drag reduction mechanism if it is at an angle-of-attack, however consideration to be given for increased moment resulting from the spike is required.