Supersonic Flow Control Research Articles

Towards transition modelling for supersonic laminar flow control based on spanwise periodic roughness elements

Laminar flow control (LFC) is one of the key enabling technologies for quiet and efficient supersonic aircraft. Recent work at Arizona State University (ASU) has led to a novel concept for passive LFC, which employs distributed leading edge roughness to limit the growth of naturally dominant crossflow instabilities in a swept-wing boundary layer. Predicated on nonlinear modification of the mean boundary-layer flow via controlled receptivity, the ASU concept requires a holistic prediction approach that accounts for all major stages within transition in an integrated manner. As a first step in developing an engineering methodology for the design and optimization of roughness-based supersonic LFC, this paper reports on canonical findings related to receptivity plus linear and nonlinear development of stationary crossflow instabilities on a Mach 2.4, 73 degrees swept airfoil with a chord Reynolds number of 16.3 million.

Numerical Studies of Laser-Induced Energy Deposition for Supersonic Flow Control

This work deals with the computational study of localized laser energy deposition in supersonic flows. A model for Nd:YAG laser energy deposition in air has been developed for this purpose. It is designed to predict the fluid dynamic effects of the energy deposition process in supersonic flows. The key physical processes are captured, including inverse bremsstrahlung absorption, evolution of the plasma shape and structure, air breakdown chemistry, and the subsequent fluid dynamics. The model is validated using measurements of experiments done in quiescent air. The effects of energy deposition in three-dimensional supersonic flow past sphere and a flow with Edney type IV shock-shock interaction were studied. The energy deposition was found to be effective in reducing the peak surface pressure, but not as effective in lowering the surface heat-transfer rate. In the case of flow with Edney type IV shock-shock interaction, a study was performed to find the optimal location for the energy deposition, for which there is maximum decrease in the surface pressure.

Shock Wave Control by Nonequilibrium Plasmas in Cold Supersonic Gas Flows

Experimental studies of shock modification in weakly ionized supersonic gas flows are discussed. In these experiments, a supersonic nonequilibrium plasma wind tunnel, which produces a highly nonequilibrium plasma flow with the low gas kinetic temperature at M = 2, is used. Supersonic flow is maintained at complete steady state. The flow is ionized by a high-pressure aerodynamically stabilized dc discharge in the tunnel plenum and by a transverse rf discharge in the supersonic test section. The dc discharge is primarily used for the supersonic flow visualization, whereas the rf discharge provides high electron density in the supersonic test section. High-pressure flow visualization produced by the plasma makes all features of the supersonic flow, including shocks, boundary layers, expansion waves, and wakes, clearly visible. Attached oblique shock structure on the nose of a 35-deg wedge with and without rf ionization in a M = 2 flow is studied in various nitrogen-helium mixtures. It is found that the use of the rf discharge increases the shock angle by 14 deg, from 99 to 113 deg, which corresponds to a Mach number reduction from M = 2.0 to 1.8. Time-dependent measurements of the oblique shock angle show that the time for the shock weakening by the rf plasma, as well as the shock recovery time after the plasma is turned off, is of the order of seconds. Because the flow residence time in the test section is of the order of 10 μs, this result suggests a purely thermal mechanism of shock weakening due to heating of the boundary layers and the nozzle walls by the rf discharge. Gas flow temperature measurements in the test section using infrared emission spectroscopy, with carbon monoxide as a thermometric element, are consistent with the observed shock angle change. This shows that shock weakening by the plasma is a purely thermal effect. The results demonstrate the feasibility of both sustaining uniform ionization in cold supersonic nitrogen and airflows and the use of nonequilibrium plasmas for supersonic flow control. This opens a possibility for the use of transverse stable rf discharges for magnetohydrodynamic energy extraction and/or acceleration of supersonic airflows.

Control of supersonic flow around bodies by means of a pulsed heat source

The influence of an external, pulse-periodic, energy supply source on the aerodynamic characteristics of a hemisphere positioned downstream is simulated.

Numerical study of a supersonic open cavity flow and pressure oscillation control

Numerical experiments were performed to study the flow structure and suppression of pressure oscillation in the M.,. = 2.5 supersonic open cavity flow problem. Numerical results show that the large pressure variation within the cavity induced by the shear layer's wavy shape produces new vortices not found in situations where M.,. < 2.5. The proposed suppression device imposes mass transfer on the cavity's aft bulkhead. The proposal is tested by replacing one of the cavity walls with a porous wall and adjoining vent chamber. Constant porosity and uniform vent-chamber pressure are assumed. Replacing the aft bulkhead with a porous wall/vent chamber combination provides the most effective suppression of pressure fluctuation, even with a porosity value as small as 0.1 for vent-chamber pressure ranging from p, to l.5py.. Mass transfer at the cavity floor and forward bulkhead are also examined, but they are found to be less effective.

Study of supersonic intersection flowfield at modified wing-body junctions

The problem of supersonic flow control using fillets and sweep for a wing-body junction has been investigated numerically using a three-dimensional Navier-Stokes code, which employs the MacCormack's time-split finite volume technique. An elliptic grid generation technique with direct control over spacing has been developed for constructing the grid at a filleted wing-body junction. The computed results for pressure distribution, particle paths, and limiting streamlines on the flat plate and fin surface for a swept fin show a decrease in the peak pressure on the fin leading edge and in the extent of the separated flow region. Moreover, the results for filleted juncture clearly show that the flow streamline patterns lose much of their vortical character with proper filleting. It has been demonstrated that fillets with a radius of three-and-one-half times the fin leading-edge diameter are required to weaken the vorticity in the horseshoe vortex by a factor of three for the Mach number and Reynolds number considered in the present study.

Passive control of supersonic asymmetric vortical flows around cones

The unsteady, compressible, thin-layer Navier-Stokes equations are used to numerically study the passive control of steady and unsteady supersonic asymmetric flows around circular and noncircular cones. The main computational scheme of the present study is an implicit upwind, flux-difference splitting, finite-volume scheme. Passive control of flow asymmetry is studied by using a vertical fin in the leeward plane of geometric symmetry and side strakes with and without thickness at different orientations. The study focuses on circular-section cones since they are the most likely section-shapes for strong flow asymmetry. Side-strake passive control is shown to be more efficient and practical than vertical-fin passive control.