Supersonic Freestream Conditions Research Articles

초음속 주유동 환경에서의 막냉각 특성 시험 연구

초음속 주유동 환경에서의 막냉각 특성 시험 연구

Supersonic cavity flows over concave and convex walls

Supersonic cavity flows are characterized by compression and expansion waves, shear layer, and oscillations inside the cavity. For decades, investigations into cavity flows have been conducted, mostly with flows at zero pressure gradient entering the cavity in straight walls. Since cavity flows on curved walls exert centrifugal force, the features of these flows are likely to differ from those of straight wall flows. The aim of the present work is to study the flow physics of a cavity that is cut out on a curved wall. Steady and unsteady numerical simulations were carried out for supersonic flow through curved channels over the cavity with L/H = 1. A straight channel flow was also analyzed which serves as the base model. The velocity gradient along the width of the channel was observed to increase with increasing the channel curvature for both concave and convex channels. The pressure on the cavity floor increases with the increase in channel curvature for concave channels and decreases for convex channels. Moreover, unsteady flow characteristics are more dependent on channel curvature under supersonic free stream conditions.

Aerodynamic force by Lamb vector integrals in compressible flow

A new exact expression of the aerodynamic force acting on a body in steady high Reynolds number (laminar and turbulent) compressible flow is proposed. The aerodynamic force is obtained by integration of the Lamb vector field given by the cross product of vorticity times velocity. The result is obtained extending a theory developed for the incompressible case. A decomposition in lift and drag contribution is obtained in the two-dimensional case. The theory links the force generation to local flow properties, in particular to the Lamb vector field and to the kinetic energy. The theoretical results are confirmed analyzing numerical solutions obtained by a standard Reynolds Averaged Navier-Stokes solver. Results are discussed for the case of a two-dimensional airfoil in subsonic, transonic, and supersonic free stream conditions.

Computational Aerodynamic Predictions of Supersonic Retropropulsion Flowfields

Supersonic retropropulsion, or the initiation of a retropropulsion phase at supersonic freestream conditions, is an enabling decelerator technology for high-mass planetary entries at Mars. Supersonic retropropulsion relies on retrothrust to decelerate the vehicle. A thrust-driven interaction of underexpanded jet flow with the shock layer of a blunt body alters the aerodynamic characteristics of the vehicle. Little literature exists on analytical and computational modeling approaches for supersonic aerodynamic-propulsive interactions at moderate thrust levels and flight-relevant conditions. This investigation is an exploratory application of a steady, turbulent computational approach to supersonic retropropulsion flowfields using modern and historical test cases. The results obtained from this approach agree reasonably well with experimental data for the locations of the bow shock, stagnation point, and Mach disk for a retropropulsion configuration with a single nozzle at the nose. The surface pressure distributions agree less favorably, showing a pressure rise toward the shoulder that was not observed in the original experiment. The flowfield structures for a peripheral retropropulsion configuration agree qualitatively with the expected structures, but proper inboard jet flow expansion and interactions between individual jet flows are likely not being captured; accordingly, pressure is preserved inboard of the nozzles to higher thrust than was observed experimentally.

Investigation of the turbulent wake flow of generic launcher configurations via a zonal RANS/LES method

A numerical analysis of the turbulent wake flow of a generic space launcher at supersonic freestream conditions (Ma∞ = 6.0 and ReD = 1.7 × 106) is performed using a zonal RANS/LES method. To investigate the influence of various components of a rocket model on the base flow, three supported wind tunnel configurations with the same main body geometry and different aft-body extensions consisting of a blunt base, a nozzle dummy, and a full flowing underexpanded TIC nozzle (Mae = 2.52, pe/p∞ = 100) are considered. Flow topologies for three cases are described in detail including an estimate of the impact of the wind tunnel model support on the flow field. To validate the applied numerical method, the computed flow fields are compared to experimental data from high-speed schlieren measurements provided by DLR Cologne. The influence of the used aft-body extensions on the steady-state and dynamic base flow characteristics is evaluated by a detailed analysis and comparison of the pressure distribution and its spectra along the base and nozzle walls for three investigated configurations. The numerical findings are compared to experimental wall pressure oscillation measurements provided by DLR Cologne. The major results are the non-negligible influence of the model support on the wake even on the strut averted side, the base drag reduction effect of the aft-expanding jet plume consisting of an increase of the base pressure level from \(p/p_\infty\approx0.2-0.25\) (blunt base and nozzle dummy configurations) up to \(p/p_\infty\approx0.7\) leading to a decrease of the base pressure drag coefficient from CDp base = 0.032 to 0.012 correspondingly, and the identified dominant low-frequency modes of the base pressure oscillations at SrD ≈ 0.05, SrD ≈ 0.1, and SrD ≈ 0.2 also detected in the experiments.

A structured grid based solution-adaptive technique for complex separated flows

A structured grid based technique is presented to enhance the predictive capability of widely used CFD codes through the use of solution-adaptive gridding. The procedure redistributes mesh points based upon an existing flowfield. A newly developed weight function employing Boolean sums is utilized to represent the local truncation error. This weight function is then used to construct forcing functions associated with an elliptic system. A NURBS representation is employed to define block surfaces for boundary point redistribution. The technique has been applied to a flowfield about a configuration of practical interest. This flowfield involves supersonic freestream conditions at angle of attack, and exhibits large scale separated vortical flow, vortex-vortex and vortex-surface interactions, separated shear layers and multiple shocks of different intensity. The results demonstrate the capability of the developed weight function to detect shocks of differing strengths, primary and secondary vortices, and shear layers adequately.

Efficient algorithm for solution of the unsteady transonic small-disturbance equation

A time accurate approximation factorization (AF) algorithm is formulated for solution of the three-dimensional unsteady transonic small-disturbance equation. The AF algorithm consists of a time linearization procedure coupled with a Newton iteration technique. Superior stability characteristics of the new algorithm are demonstrated through applications to steady and oscillatory flows at subsonic and supersonic freestream conditions for an F-5 fighter wing. For steady flow calculations, the size of the time step is cycled to achieve rapid convergence. For unsteady flow calculations, the AF algorithm is sufficiently robust to allow the step size to be selected based on accuracy rather than on stability considerations. Therefore, accurate solutions are obtained in only several hundred time steps yielding a significant computational cost savings when compared to alternative methods.

Symmetric Body Vortex Wake Characteristics in Supersonic Flow

An extensive experimental investigation of the symmetric body vortex wake was conducted. Cone probe measurements were made on the leeside of an ogive nose circular cylinder for three different supersonic freestream conditions. Measurements of total pressure, Mach number, and three orthogonal velocity components were made at four angles of attack of the body at various axial stations. In the present paper these data are processed to infer the position of the primary body vortex and vortex feeding sheet in the cross-flow plane, local circulation distribution in the cross-flow plane, vortex core size, wake height, and total circulation in the cross-flow plane. A detailed discussion of the results and data processing is presented.