Blunt Body Configuration Research Articles

Influence of catalytic wall on the effective radius of a blunt body geometry in a nonequilibrium hypersonic flow

The effect of the surface catalycity on the effective radius of a blunt body geometry in hypersonic flow is numerically investigated. The blunt body geometry is defined in terms of a body radius with variation in both nose radius and the corner radius. Five different types of blunt body configurations are considered, that range from a flat-faced to a complete hemisphere geometry. The chosen blunt body configurations are investigated for four flow conditions with different levels of flow enthalpy. The effective radius is obtained by comparing the stagnation heat transfer of the blunt body geometry to that of the spherical geometry. To compute the stagnation heat transfer in the given blunt body configuration, a two-dimensional computational fluid dynamics (CFD) solver with thermochemical non-equilibrium is utilized. Both non-catalytic and fully-catalytic wall boundary conditions are considered in the computation. The obtained effective radius is additionally compared with the original data provided in the literature. The results show that surface catalycity influences the effective radius for the given blunt body configuration.

Three-dimensional numerical modeling of flow upstream of a symmetric streamlined body mounted over a flat plate with tip gap

In this research activity numerical simulations are carried out to investigate the flow field upstream of a symmetric streamlined body mounted perpendicular to a flat plate with and without clearance gap between the tip of the streamlined body and the flat plate with laminar boundary layer. The developed numerical model successfully predicted the three-dimensional horseshoe vortex system upstream of the streamlined body with and without the tip gap. The resulting vortex system for the configuration with tip gap contains multiple vortices with characteristics similar to that of end-wall-flows of surface-mounted obstacles. The effects of varying tip gap clearance for various values of free stream Reynolds number are also investigated. It was found that the introduction of a gap between the streamlined body tip and flat surface caused shifting of the vortex structure system in the upstream direction. Moreover, it is observed that the free stream Reynolds number and the tip gap between the streamlined body and the flat plate substantially influences the unsteady character of the flow field and the vortex system structure. Results obtained from the numerical simulations are compared with experimental measurements of a blunt body configuration and have been found in good agreement.

Thermo-Fluid Analysis of Supersonic Flow Over Ballistic Shaped Bodies with multiple aero-disk spike configurations

The aerodynamics of re-entry vehicles has always been in the forefront among space research. With the increasing interests in space exploration, it is important to understand the aerodynamics of spacecrafts and identify an optimum design to overcome the forces due to the earth's atmosphere. In this paper, Computational Fluid Dynamic (CFD) analysis has been carried out on ballistic bodies with a single, double and triple aero-disk spikes. The study also involves the presence and absence of a blunt tip to aid the analysis of flow behaviour on these bodies under two scenarios namely zero-degree angle of attack and at supersonic speed (Mach 2.0). The aerodynamic drag and surface heat transfer effects of these spikes on three different blunt body configurations has been studied. The shape of the blunt bodies vary based on the nose bluntness factor. The flow patterns of these configurations were three-dimensionally visualized via Schlieren-like, Mach and Pressure contours. It was observed that the usage of aero-disk spike reduced the aerodynamic drag by 45%–60% when compared to the bodies without spikes. The configuration labelled 3221 showed the maximum effect with an average drag reduction of more than 55%. There was a remarkable drop in the stagnation point value of surface heat flux with the addition of all five spike system. An efficient performance of localized peak heat fluxes was also noticed upon the addition of double and triple spike systems. In conclusion, it has been observed that the usage of double and triple spikes on the 3221 blunt body has significantly improved its aerodynamic drag and its surface heat flux.

Aerothermodynamic Assessment of Spiked Configuration for Drag Reduction at Hypersonic Speeds

Aerothermodynamic analysis was performed for blunt-body configurations with spikes mounted to determine drag reduction effectiveness. In-house perfect gas and chemical nonequilibrium solvers were utilized. The analysis revealed that flow separation and associated shock restructuring are responsible for drag reduction. Two vortices occurred in the separation zone for shorter spikes, whereas three vortices occurred for longer-spike simulations. The downstream shift of upstream influence location on the spike and upstream shift of flow reattachment location as well as the shock impingement point on the body surface were determined for high-enthalpy freestream conditions. These alterations in the flow field and the related reduction in separation bubble size led to a reduction of the effectiveness of the spike in reducing the drag force. About 13%–16% reduction in the effectiveness was found for the 4.0-MJ/kg case and sharp-spike mounting. The reduction of effectiveness was lower for longer spikes. These real gas effects were responsible for an increase in wave drag and friction drag for high-enthalpy flow over a spiked configuration. Therefore it is recommended to account for the real gas effects when considering a spike as a drag-reducing device.

Vibration analysis of transverse galloping of different bluff bodies

The purpose of this research is to identify the best Blunt Body (BB) configuration for a piezoelectric wind energy harvesting system. The bluff body configurations studied are square, trapezoid, cone, cylinder, and aerofoil which are experimented on the rectangular and triangular cantilever beam. The increase in displacement and vibration velocity with respect to incident wind velocity is reported experimentally. Experimental findings suggest square BB and triangular cantilever are best suited for transverse galloping. A comprehensive study of galloping of the cantilever beams on its various regions with respect to the wind velocity is done. An overall increase of 27% displacement is reported in the triangular cantilever beam when compared to the rectangular cantilever beam. Cut–in speed for the above configurations is also studied and results are plotted. Results prove Trapezoidal BB and aerofoil BB has the least and highest cut-in speed respectively.

Computational simulations of near-continuum gas flow using Navier-Stokes-Fourier equations with slip and jump conditions based on the modal discontinuous Galerkin method

Blunt-body configurations are the most common geometries adopted for non-lifting re-entry vehicles. Hypersonic re-entry vehicles experience different flow regimes during flight due to drastic changes in atmospheric density. The conventional Navier-Stokes-Fourier equations with no-slip and no-jump boundary conditions may not provide accurate information regarding the aerothermodynamic properties of blunt-bodies in flow regimes away from the continuum. In addition, direct simulation Monte Carlo method requires significant computational resources to analyze the near-continuum flow regime. To overcome these shortcomings, the Navier-Stokes-Fourier equations with slip and jump conditions were numerically solved. A mixed-type modal discontinuous Galerkin method was employed to achieve the appropriate numerical accuracy. The computational simulations were conducted for different blunt-body configurations with varying freestream Mach and Knudsen numbers. The results show that the drag coefficient decreases with an increased Mach number, while the heat flux coefficient increases. On the other hand, both the drag and heat flux coefficients increase with a larger Knudsen number. Moreover, for an Apollo-like blunt-body configuration, as the flow enters into non-continuum regimes, there are considerable losses in the lift-to-drag ratio and stability.

Effects of injection on heat transfer and the boundary-layer instability for a hypersonic blunt body configuration

The wall normal gas injection effect on the heat transfer and the boundary-layer stability is investigated for the high-speed flow over hemispherical model of space vehicle. The heat flux distributions on the body surface are obtained using numerical solutions of the Navier-Stokes equations for laminar axisymmetric flow. The boundary layer stability is analyzed using the linear stability theory and the eN method. Good agreement between computational and experimental heat flux distributions is obtained at zero and small injection rates. It is shown that the transition onset, which was experimentally observed in the boundary layer with injection, is associated with small values of the integral amplification of instability. This indicates that in the experiment laminar-turbulent transition is governed by bypass mechanisms relevant to inherently nonlinear interactions and/or the transient growth of non-orthogonal modes.

Reduction of wave drag on parameterized blunt bodies using spikes with varied tip geometries

Aeospike based wave drag reduction is investigated using two-equation turbulence model applied to Faver averaged Navier Stokes solver. Three different blunt bodies are considered in a low supersonic stream of Mach number 2. The considered blunt bodies differ in their degree of bluntness defined in terms of half cone angle, area of flattened front side and radius of bluntness. The zero angle of attack flowfield around these three bodies are computationally analyzed with and without the presence of aft spikes to evaluate the wave drag resulting from the formation of front shock structure. The influence of spike configuration on the wave drag is also investigated. The various considered spike tip geometries include aero-disk, sharp and blunt with the length of all the spikes being equal to the base diameter of the blunt bodies (L/D = 1). It has been found that the 3221 blunt body when coupled with a blunt tipped spike yielded the lowest drag coefficient of 0.3, despite the 3221 having the highest standalone drag coefficient of 0.86, among the blunt bodies when simulated individually without spikes. The physics behind the wave drag reduction associated with each combination of blunt body and spike configuration is presented with clarity. This study portrays the importance of taking bluntness factor, semi-cone angle, fineness ratio and blunt body shape factor into consideration while proposing the generalized optimum spike configuration for minimum drag attainment.

Blunt-Body Paradox and Improved Application of Transient-Growth Framework

The Reshotko–Tumin transition criterion based on optimal transient growth successfully correlates laboratory measurements of roughness-induced transition over blunt-body configurations. Even though transient growth has not been conclusively linked to the measured onset of transition, the correlation denotes the only available physics-based model for subcritical transition in blunt-body flows, since the latter do not support any modal instabilities at typical experimental conditions. Unlike other established models based on empirical curve fits that are valid for a specific subclass of datasets, the optimal-growth-based transition criterion appears to provide a reasonable correlation with measurements in various wind tunnel and ballistic-range facilities and for a broad range of surface-temperature ratios. This paper is focused on optimal-growth calculations that improve upon significant shortcomings of the computations underlying the Reshotko–Tumin correlation. The improved framework is applied to leeward transition over a spherical-section forebody. The computed results highlight the significance of nonparallel basic-state evolution, curvature terms, and an optimization procedure that varies both inflow and outflow locations of the interval. More importantly, the results indicate that the modified correlation is very close to its original form and hence that the accuracy of the transient-growth-based transition criterion is not compromised by using a more thorough theoretical framework. Yet the results also show that the optimal energy gain up to the predicted transition onset location can be rather small, highlighting the need to further investigate the optimal-growth criterion for additional experimental configurations and to also uncover the in-depth physics underlying blunt-body transition.

Fluid-thermal analysis of aerodynamic heating over spiked blunt body configurations

When flying at hypersonic speeds, the spiked blunt body is constantly subjected to severe aerodynamic heating. To illustrate the thermal response of different configurations and the relevant flow field variation, a loosely-coupled fluid-thermal analysis is performed in this paper. The Mesh-based parallel Code Coupling Interface (MpCCI) is adopted to implement the data exchange between the fluid solver and the thermal solver. The results indicate that increases in spike diameter and length will result in a sharp decline of the wall temperature along the spike, and the overall heat flux is remarkably reduced to less than 300W/cm2 with the aerodome mounted at the spike tip. Moreover, the presence and evolution of small vortices within the recirculation zone are observed and proved to be induced by the stagnation effect of reattachment points on the spike. In addition, the drag coefficient of the configuration with a doubled spike length presents a maximum drop of 4.59% due to the elevated wall temperature. And the growing difference of the drag coefficient is further increased during the accelerating process.

Assessment of Real Gas Effects on Approximate and Boundary Layer Equations for Hypersonic Laminar Flow over Axisymmetric Bodies

Two efficient computational procedures based on the boundary layer equations and approximate relations areassessedin prediction of the laminar hypersonic flowfield for both the perfect gas and equilibrium air around the axisymmetric blunt body configurations. For the boundary layer procedure, the boundary layer equationsutilize the integral matrix solution algorithm for the blunt nose and after body region by using a space marching technique. The integral matrix procedure able us to create accurate and smooth results using the minimum grid in the boundary layer and minimize the computational costs. Applying the approximate method creates a robust and efficient code for heating calculations over the blunt bodies which flies in hypersonic regimes. These algorithms are highly appropriate to design of hypersonic reentry vehicles. The effects of real gas on the flowfield characteristics are also studied in two procedures.

Integrated Analysis of Reusable Thermal Protection Systems Based on Variable-Transpiration Cooling

Reusable thermal protection systems are one of the key technologies that have to be improved to use hypersonic vehicles as practical, long-range, transportation systems. The proposed concept of variable-transpiration cooling is investigated in this work by coupling the hypersonic boundary-layer solution with the thermal response of a porous material. The simulations of the hypersonic boundary layers are obtained using an in-house-developed reduced-order model capable of handling generic injection velocity profiles at the porous wall and the high-fidelity computational-fluid-dynamics code Langley Aerothermodynamic Upwind Relaxation Algorithm. The material thermal response is included adopting a one-dimensional model for the porous medium. The integrated analysis is performed for a flat plate and a two-dimensional blunt-body configuration. A sawtooth wall velocity profile was chosen to represent the variable-transpiration strategy. The uniform transpiration on the blunt body allows for a reduction of the stagnation point heat flux by 48% in comparison with the case without transpiration. The variable transpiration reduces the stagnation point heat flux by an additional 8%. The integrated analysis highlights the coolant blockage effects, the potential offered by the variable-transpiration cooling, and the necessity of performing a coupled flow-material analysis, at the design stage, to define realizable combinations of porosity, thermal conductivity, and material thickness capable to guarantee the thermostructural integrity of the thermal protection system.

An analytical approach for stand-off distance of detached shock waves

An analytical model for prediction of shock stand-off distance in front of blunt bodies was derived based on dimensional analysis. Despite of existing models, it is not limited to a specific geometry or a special range of Mach number. Five blunt body configurations were studied to verify accuracy of this mathematical model. A CFD code was established and validated by existing experimental data and shock stand-off distance (SSOD) in front of these configurations was obtained by this CFD code and used for validation of the analytical model that confirmed its accuracy. SSOD was computed by inviscid flow and various turbulence models in order to investigate effects of viscosity and turbulence modeling on it.

Comparison between the two-equation turbulence models of Jones and Launder and of Wilcox and Rubesin applied to aerospace problems

In the present work, the Van Leer flux vector splitting scheme is implemented on a finite-volume context. The two-dimensional Favre-averaged Navier-Stokes equations are solved using an upwind discretization on a structured mesh. The Jones and Launder and the Wilcox and Rubesin two-equation models are used in order to close the problem. The physical problems under studies are the low supersonic flow along a ramp and the moderate supersonic flow around a blunt body configuration. The implemented scheme uses a MUSCL (Monotone Upstream-centered Schemes for Conservation Laws) procedure to reach second order accuracy in space. The time integration uses a Runge-Kutta method of five stages and is second order accurate. The algorithm is accelerated to the steady state solution using a spatially variable time step. This technique has proved excellent gains in terms of convergence rate as reported in Maciel. The results have demonstrated that the Wilcox and Rubesin model has yielded more critical pressure fields than the ones due to Jones and Launder. The shock angle of the oblique shock wave in the ramp problem and the stagnation pressure ahead of the blunt body configuration are better predicted by the Wilcox and Rubesin turbulence model. Key words: Van Leer algorithm, Jones and Launder turbulence model, Wilcox and Rubesin turbulence model, finite volumes and structured discretization, Navier-Stokes equations.

Dual-code solution procedure for efficient computing equilibrium hypersonic axisymmetric transitional/turbulent flows

An appropriate combination of the thin-layer Navier–Stokes (TLNS) and parabolized Navier–Stokes (PNS) solvers is used to accurately and efficiently compute hypersonic transitional/turbulent flowfields of perfect gas and equilibrium air around blunt-body configurations. The TLNS equations are solved in the nose region to provide the initial data plane needed for the solution of the PNS equations. Then the PNS equations are employed to efficiently compute the flowfield for the afterbody region by using a space marching technique. Both the TLNS and the PNS equations are numerically solved by using the implicit non-iterative finite-difference algorithm of Beam and Warming. A shock fitting procedure is used in both the TLNS and PNS codes to obtain accurate solution in the vicinity of the shock. For turbulent flow simulations, both the Cebeci–Smith (CS) and the Baldwin–Lomax (BL) turbulence models are analyzed with the present technique for the case of long slender blunt bodies. The Baldwin–Lomax turbulence model, which does not need the determination of the edge of the boundary layer, is modified in the present work to include the effects of variable properties and damping factor to accurately calculate flowfield characteristics in turbulent regions. Detailed comparisons are made with other numerical and experimental results to assess the accuracy and efficiency of the present solution procedure for computing hypersonic transitional/turbulent flows over long slender blunt bodies. The results of these computations are found to be in good agreement with available data. The effects of real gas on the flowfield characteristics are also studied.

Experimental Investigation of the Effects of Aerospike Geometry on Aerodynamic Drag and Heat Transfer Rates for a Blunt Body Configuration at Hypersonic Mach Numbers

The effects of aerospike geometry on the drag reduction and heat transfer rates for a large-angle blunt cone flying at hypersonic Mach numbers are investigated in a hypersonic shock tunnel. Two spike geometries are considered. The first is a plain spike with a conical tip and the second is a telescopic aerospike fitted with discs of decreasing diameter in the direction opposite to the flow direction. These aerospikes are fitted to a 120° apex-angle blunt cone and results are investigated at free stream Mach numbers of 5.75 and 7.9 for different angles of attack. The aerodynamic forces are measured using an accelerometer-based force balance system and the heat transfer rates are measured using platinum thin film sensors. It is found that the telescopic aerospike has better drag reduction performance at angles of attack beyond 2° while the performance of the plain aerospike is better for angles of attack closer to zero degrees.

Structured high resolution algorithms in the solution of the euler equations in the two-dimensional space

The present work compares the high resolution schemes of (1) Yee, Warming and Harten, (2) Harten, (3) Yee and Kutler and (4) Hughson and Beran applied to the solution of aeronautical and aerospace problems. All schemes are TVD flux difference splitting type and are second order accurate in space. The Euler equations in conservative form, employing a finite volume formulation and a structured spatial discretization, are solved in two-dimensions. The time integration is performed by a dimensional splitting method and is first order accurate. The steady state physical problems of the supersonic flows along a ramp and around a blunt body configuration are studied. In the ramp problem, the Hughson and Beran scheme was the most critical because presented the most intense pressure field and the most intense Mach number field. Moreover, this scheme predicts the best value to the shock angle of the oblique shock wave. The shock and the expansion fan pressure distributions are better captured by the Yee, Warming and Harten and the Yee and Kutler schemes. In the blunt body problem, the Harten scheme presented the most intense pressure field. The Harten scheme estimates the best value to the stagnation pressure on the configuration nose.

Comparison among structured first order algorithms in the solution of the euler equations in two-dimensions

The present work studies upwind schemes applied to the solution of aeronautical and aerospace problems. The Harten, the Frink, Parikh and Pirzadeh, the Liou and Steffen and the Radespiel and Kroll algorithms, all first order accurate in space, are studied. The Euler equations in conservative form, employing a finite volume formulation and a structured spatial discretization, in the two-dimensional space, are solved. A time splitting method and a Runge-Kutta method of five stages are used to perform the time march of the numerical schemes. The steady state physical problems of the supersonic flow along a ramp and around a blunt body configuration are studied. All algorithms are accelerated to the steady state solution using a spatially variable time step. This technique has proved excellent gains in terms of convergence ratio as reported in Maciel. The results have demonstrated that the Liou and Steffen scheme has presented the most critical solutions, in both example-cases, in relation to the others schemes and a more accurate solution, in terms of the determination of the stagnation pressure in the blunt body case, than the Harten and the Radespiel and Kroll schemes. In the ramp problem, the Harten scheme predicts the best pressure distribution along the ramp wall in comparison with theoretical results. In the blunt body problem, the Liou and Steffen scheme presents the highest value of Cp at the configuration nose in relation to the other schemes. Values of cL and cD have been accurately predicted by all schemes, except by the Harten scheme.

Dual-code solution procedure for efficient computing equilibrium hypersonic axisymmetric laminar flows

An appropriate combination of the thin-layer Navier–Stokes (TLNS) and parabolized Navier–Stokes (PNS) solvers is used to accurately and efficiently compute hypersonic flowfields of equilibrium air around blunt-body configurations. The TLNS equations are solved in the nose region to provide the initial data plane needed for the solution of the PNS equations. Then the PNS equations are employed to efficiently compute the flowfield for the afterbody region by using a space marching procedure. Both the TLNS and PNS equations are numerically solved by using the efficient implicit non-iterative finite-difference algorithm of Beam and Warming. A shock fitting technique is used in both the TLNS and PNS codes to obtain accurate solution in the vicinity of the shock. In the regions of the flowfield with upstream influences, the globally iterated PNS (IPNS) equations, which are computationally more efficient than the TLNS equations, can be used to improve the accuracy of the results. To validate the results of the developed TLNS code and study real gas effects on the flowfield, hypersonic laminar flow over a sphere at Mach number of 11.26 is computed. The computations are performed for hypersonic laminar flow over 5° long slender blunt cone at Mach number of 19.25 to demonstrate the accuracy and efficiency of using the present TLNS-PNS methodology. To show the capability and robustness of the present solution procedure, the comparisons are also made with the wall heat-transfer data on a 12.84 ° / 7 ° bicone at Mach number of 6.89 and freestream temperature of 1604 K. The results of these computations are found to be in good agreement with available numerical and experimental data. The results of the perfect gas for these cases are also presented and the effects of real gas on the flowfield characteristics are studied in both the TLNS and PNS solutions.