Boat-tail Region Research Articles

Flow Field Over Boat-Tail Region of Heat Shield of a Typical Launch Vehicle at Mach 2

Boat-tailed heat shields offer a higher payload volume but lead to flow separation and associated effects. In the present paper an attempt is made to find out the effect of boat-tail angle on the over all flow field with special emphasis on acoustic load near the boat-tail region. Experiments and CFD routes are used to investigate the flow field. Experiments consist of steady and unsteady pressure measurements and flow visualisation through schlieren and oil flow. CFD simulations are also carried out for the wind tunnel conditions. Results indicate that fluctuating pressure co-efficient increases with flow separation, peaks at reattachment point and reduces further downstream. An Increase in boat-tail angle from 20" to 30" leads to about I2Vo increase in acoustic load-s. All these studies were carried out at a Mach number of 2 and a Reynolds number of 4 x t}o based on model length.

Numerical Flowfield Visualization Over Heat Shield Of Satellite Launch Vehicle at Mach 0.8 - 3.0

The paper presents a numerical flowfield visualization over a typical payload shroud of a satellite launch vehicle at Mach number range of 0.80 -3.0 and Reynolds number range of 33 x 106 - 46 x 106 /m. The numerical simulation over the bulbous heat shield is carried out by solving time-dependent compressible axisymmetric turbulent Reynolds-averaged NavierStokes equations. The closure of these equations is obtained employing the Baldwin-Lomax turbulence model. A three-stage Runge-Kutta time-stepping scheme has been used in conjunction with finite-volume discretization of the computational domain. The flowfield features over the bulbous heat shield have been analyzed from the velocity vector and the density contour plots. Flow separation on the payload shroud due to the normal shock wave is observed at Mach number 0.80 and 0.90. The normal shock movement on the heat shield is simulated for various transonic Mach number. A recirculation zone of flowfield is formed in the boat-tail region of the heat shield. The vorticity formation ahead of the heat shield moves close to the heat shield with the increasing transonic Mach number, which is observed in the density contours plots of the flowfield. Shock stand-off distance at the supersonic speed is calculated and compared with asymptotic formula of Frank and Zierep. They are found in good agreement.

Computation of three - dimensional transonic flow fields over a three - body launch vehicle configuration for low angle of attack conditions

The present work aims at the prediction of shock wave position on the heat shield region of a three body launch vehicle in transonic region. The launch vehicle consists of a cylindrical core body and two boosters. The core body is made of a spherical nose, followed by a cone and heat shield region which is a flat surface. The heat shield is followed by a boat tail. Simulations are performed with commercial CFD package, ANSYS –FLUENT. Reynolds stresses are computed using the k-ω SST turbulence model. Explicit time integration is used to obtain steady-state solutions. A structured grid over the vehicle is generated using ICEMCFD software. In the near-wall region of the launch vehicle fine mesh is employed to capture the boundary layer. Simulations are performed for angle of attacks (AOA) 0° and 4° for Mach number 0.95. The computed nose stagnation pressure compared with the isentropic relations and deviation found to be .067%. A standing normal shock wave is observed for AOA 0 whereas an oblique shock wave is observed for angle of attack 4°. The predicted flow structure in terms of density distribution is compared with experimental schlieren images. The predictions captured essential flow features such as expansion around the conical part, boundary layer over the heat shield, shock wave on the heat shield, and flow separation in the boat tail region. The predicted flow structure and shock wave position for AOA O matched well with the experiments. However, for AOA 4°, the deviation between flow structure and shock position is noticed. Possible reasons for the deviation are explained.

Influence of Geometrical Parameters of Heat Shield on Flow Characteristics at Transonic Mach

The numerical simulation over the bulbous heat shield is carried out by solving time-dependent compressible axisymmetric turbulent Reynolds-averaged Navier-Stokes equations. The solution of these equations is obtained employing the Baldwin-Lomax turbulence model. A three-stage Runge-Kutta time-stepping scheme has been used in conjunction with finite-volume discretization of the computational domain. The flowfield features over the bulbous payload shroud have been analyzed using the density contour plots and surface pressure distributions. Flow separation on the payload shroud due to the terminal shock wave is observed at transonic Mach numbers range. The normal shock movement on the heat shield is simulated for various transonic Mach numbers. The maximum diameter of the various heat shields is kept constant in order to evaluate the movement of terminal shock. A recirculation zone of the flowfield is formed in the boat-tail region of the payload shroud. The density increases ahead of the stagnation region of the heat shield moves close to the heat shield with the increasing transonic Mach number. It also depends on the cone angle of the heat shield as observed in the density contours plots of the flowfield.

Computational Analysis of the Flow Field Near the Boat-tail Region of Annular Plug Nozzles.

Flow fields over annular plug nozzles are computationally simulated and the boat-tail drag characteristics are clarified and discussed based on the simulation results. The plug nozzle configuration is taken from the ATREX (Air Turbo Ramjet) engine under development at the ISAS. The simulations are carried out for the axi-symmetric nozzle configuration using compressible Navier-Stokes equations. The computed result shows that there exists a low pressure region downstream of the Prandtl-Meyer expansion on the boat-tail region and the separation shock wave appears due to the interaction of the main flow and the nozzle plume downstream. The result also shows that the primary cause of the boat-tail drag turns out to be the low pressure region downstream of the Prandtl-Meyer expansion. The flow field with the secondary flow injection is then simulated and the computed result shows that the pressure in the region in front of the separation shock wave increases and the secondary flow injection successfully reduces the boat-tail drag. The effect of the turbulence model used in the computation is discussed to ensure the reliability of the solutions.

Comparative study of surface pressure fluctuations over bulbous heat shields at Mach number=0.95

Time-dependent turbulent compressible Reynolds-averaged Navier–Stokes equations are solved for computing flowfield over the bulbous payload shroud of a satellite launch vehicle at a freestream Mach number of 0.95 and at a zero angle of attack. Numerical simulation has been carried out employing a multistage Runge–Kutta time-stepping scheme in conjunction with a finite volume discretization. The closure of these equations is achieved using the Baldwin–Lomax turbulence model. Comparisons have been made between numerical and experimental results such as schlieren pictures, position of terminal shock on forebody cylinder and surface pressure distributions. A good agreement is found between them. A separated flow zone on the boat tail region is observed and is found to be having unsteady pressure fluctuations. Standard deviation, higher-order moments and spectrum of surface pressure levels of the fluctuating surface pressure are analysed in the separated flow region of the boattail of the heat shield. A comparative study of surface pressure fluctuations and spectrum of sound pressure levels has been made for two different types of heat shield configurations that are close to the recommended NASA specifications.

Unsteady pressure fluctuations in the boattail region of a heat shield

Unsteady, turbulent, compressible, axisymmetric, Reynolds-averaged Navier–Stokes equations are solved for the flow past a bulbous payload shroud for a freestream Mach number of 0.95 and Reynolds number of 16.40×10 6. A time-dependent numerical simulation is carried out using a finite-volume discretization technique in conjunction with a multistage Runge–Kutta time-stepping scheme. The closure of the system of equations is achieved using the Baldwin–Lomax turbulence model. Comparisons have been made with experimental results such as the schlieren picture and surface pressure distribution. A good agreement is found between them. A separated flow zone on the boattail region is observed and is found to be highly unsteady. Standard deviation, higher-order moments, histograms, and spectrum of surface pressure levels are analysed in the separated region of the boattail.

Euler solution of axisymmetric jets in supersonic external flow

Conclusions A numerical experiment of axisymmetric turbulent viscous flow over a bulbous heat shield is performed by employing a three-stage Runge-Kutta time-stepping scheme. Turbulence closure is achieved using the Baldwin-Lomax turbulence model. The flowfield visualization of the terminal shock and the separated region helps in a systematic understanding of flow structure under various freestream Mach numbers. The following observations are made based on the described numerical simulations. 1) The terminal shock moves downstream with increasing freestream Mach number. The strength of the terminal shock initially increases with Mach number and later decreases. The location of the terminal shock is found as a nonlinear function of the freestream Mach number. 2) The separation zone in the boat-tail region is found as a function of the freestream Mach number. The flowfield features of the separated region are found to be different in the transonic and supersonic Mach number ranges.

Transonic Navier-Stokes solutions about a generic hypersonic configuration

Three-dimensional transonic viscous flow computations are presented for a generic high-speed accelerator model that includes wing, body, fillets, and a no-flow-through engine nacelle. Solutions are obtained from an algorithm for the compressible Navier-Stokes equations that incorporates an upwind-biased, flux-vector-splitting approach along with longitudinally patched grids. Results are presented for fully turbulent flow assumptions and include correlations with wind-tunnel data. A good quantitative agreement for the forebody surface pressure distribution is achieved between computations and the available wind-tunnel measurements at My = 0.9. Furthermore, it is demonstrated that the flow is stagnating around the boattail region due to separation from the aft-engine cowl lip.

Supersonic flow simulation for a boat-tailed heat shield

SummaryFor a 15° boat-tailed heat shield or payload shroud, the unsteady, compressible Navier-Stokes equations are numerically solved. For a Reynolds number of the order of one million and for four different freestream Mach numbers, the time integration is performed for 64 x 30 grid computational domain. The entire flow-field is analysed to delineate the gross dominant characteristics. It is observed that the flow in the boat-tail region is completely attached for Mach number 2·47 and beyond whereas it is separated for lower Mach numbers. A comparison between the numerical solutions and the available experimental results is provided and, for incipient flow separation conditions, an evaluation of unsteady surface pressure data is presented.

Effects of transonic buffeting on a hammerhead-shaped payload.

An analytical and experimental program was conducted to improve the capability of determining the effects of transonic buffeting on pay loads of launch vehicles. An analytical method was developed to apply experimental data, using power spectral techniques, in the analytical prediction of vehicle structural loads. To solve the loads problem without unsupported assumptions, a wind-tunnel test was conducted on a hammerhead-shaped pay load to measure the needed power spectral and cross-power spectral density functions of the local buffeting forces or pressures. The reduced experimental data, circumferential correlations of unsteady pressures, longitudinal correlations of unsteady pressures and local normal force, power spectra and cross-power spectra of unsteady pressures, and local normal force for freestream Mach number 0.91, and angle of attack of 0° to 6° are illustrated. These data indicate large negative values of longitudinal correlation between fluctuating pressures and local normal force in the boattail region. Bending moment responses were computed on a launch vehicle using measured cross-correlation or cross-power spectra between the buffet disturbances. The responses were smaller than that computed using zero correlation between the disturbances, and larger than the calculated response caused by atmospheric turbulence.