Ihab Girgis

Creation of Steering Moments in Supersonic Flow by Off-Axis Plasma Heat Addition

In this paper, the change in aerodynamic forces as a result of local heat addition, upstream of a cone, to supersonic flow (Mach 3.0) is studied numerically. In principle, such an effect on the forces and moments can be used for vehicle steering as well as drag reduction. Local energy addition to the flow is achieved by the use of microwave radiation as a heating source and an electron beam to control the air conductivity and consequently the location of the energy deposition. Since steering creation requires heating in a localized pre-ionized region, the strength of the microwave field has to be much lower than the critical value of the electric field at breakdown. Results show the potential effects of heat addition on the aerodynamic forces. The corresponding power and the optimized location require d to achieve these effects are discussed. 1. Introduction

Virtual Shapes in Supersonic Flow Control with Energy Addition

This paper presents a short selective review of theoretical and experimental studies conducted by the authors and their collaborators during the past few years in areas related to supersonic and hypersonic flow regimes with applications such as drug reduction, inlet and effective vehicle geometry control in off-design flight regimes, and steering and sonic boom mitigation. Their results suggest a principal possibility to enable transitions between the propulsion modes and ramjet startup and to minimize the need for the traditional isolator stage, as well as to increase the inlet mass capture at Mach numbers below the design value, using active control based on virtual shapes created by energy addition upstream of the inlet throat. A common feature of all these substantially different applications and processes is a power deposition into a supersonic flow which results in the creating of virtual shapes, modifying flowlike solid obstacles immersed in it. The virtual shapes can be created by microwave plasma heating, magnetohydrodynamic forces, electron beams, and localized plasma-assisted surface combustion. The power necessary to operate plasmas can come either from the turbine at mode transition, from an auxiliary power unit, or, as suggested in a new bypass concept, from a magnetohydrodynamic generator either placed downstream of the combustor or collocated with it.

Nonlinear mechanics of wavy instability of steady longitudinal vortices and its effect on skin friction rise in boundary layer flow

Wavy secondary instability of steady longitudinal vortices in boundary layer flow is studied. The nonlinear interaction problem is parabolized through scaling guided by observations. Emphasis is placed on the nonlinear modification of the steady problem by the Reynolds stresses of the wavy disturbance. It is found that the skin friction in such a modification process increases well above the local turbulent boundary layer value.

Steering Moments Creation in Supersonic Flow by Off-Axis Plasma Heat Addition

The change in aerodynamic forces as a result of local plasma heat addition to supersonic flow (Mach 3.0), upstream of a cone, is studied numerically by solving the three-dimensional compressible Euler equations. In principle, such an effect on the forces and moments can be used for vehicle steering as well as drag reduction. Local energy addition to the flow is achieved by the use of microwave radiation as a heating-source and an electron beam to control the air conductivity and consequently the location of the energy deposition. This approach requires heating only in a localized preionized region, and so the strength of the microwave field has to be much lower than the critical value of the electric field at breakdown. Results show the potential effects of heat addition on the aerodynamic forces. The corresponding power and the optimized location required to achieve these effects are discussed.

Fluid Mechanics of a Mach 7-12 Electron Beam Driven Missile Scale Hypersonic Wind Tunnel: Modeling and Predictions

Models of increasing complexity have been developed for the design and simulation of the axisymmetric inviscid fluid mechanics and energy addition of an electron-beam driven hypersonic wind tunnel for missile-scale testing and development. The principal target has been a Mach-12 capability at altitudes of approximately 25 km and above with a test section of 1.3 m. Also, results for lower Mach numbers at lower altitudes down to Mach-7 at 2 km have been obtained. The fully coupled e-beam and Euler flow simulation shows that with a magnetically guided, 3 MeV e-beam and a nozzle geometry determined from the solution to an optimization problem, shock waves can be eliminated notwithstanding the very high radiative power (200 MW) that is deposited into the core flow (away from the boundary layer). While there remain many issues to be resolved, we have not yet found an intrinsic problem with either the concept or its application to such long run time, missile-scale, facilities.

Steady and Unsteady Supersonic Flow Control with Energy Addition

This paper presents a review of some experimental and theoretical results obtained by the authors and their collaborators during the past few years, including: • The effect of a plasma (directed-energy) air spike in supersonic/hypersonic flows . The similarity laws for shock wave and drag parameters, as functions of the strength of heat source and characteristics of incident flow, and experimental and computational parametric studies are discussed. • Modeling of “virtual cowl ,” i.e., of energy addition to hypersonic flow off the vehicle in order to increase air mass capture and reduce spillage in scramjet inlets at Mach numbers below the design value. • Numerical studies of aerodynamic forces created by off-axis heat addition upstream of a body. These forces and moments can be used for supersonic/hypersonic vehicle steering. • Experiments and numerical modeling of pulsed off-body energy addition for sonic boom mitigation.

Predictions for the Heat Transfer and Boundary Layer Growth in the Radiatively Driven Hypersonic Wind Tunnel and Comparisons with Experiment at Ultra High Reynolds Number (Invited)

American Institute of Aeronautics and Astronautics For permission to copy or to republish, contact the copyright owner named on the first page. For AIAA-held copy-right, write to AIAA Permissions Department, 1801 Alexander Bell Drive, Suite 500, Reston, VA, 20191-4344. 22 AIAA Aerodynamic Measurement Technology and Ground Testing Conference 24-26 June 2002 / St. Louis, MO AIAA-2002-3128 Predictions for the Heat Transfer and Boundary Layer Growth in the Radiatively Driven Hypersonic Wind Tunnel and Comparisons with Experiment at Ultra High Reynolds Number (Invited)

RDHWT/MARIAH II Energy Addition Modeling and Experiments Review

The viability of the Radiatively-Driven Hypersonic Wind Tunnel (RDHWT)/ MARIAH II project rests on our ability to controllably and predictably add energy to a supersonic air flow downstream of the throat with a high power electron beam. Experiments conducted at Sandia National Laboratories during the Spring of 2003 deposited over 800 KW of power into the flow in a successful demonstration of that concept. A detailed analysis of the streamwise pressure distribution and other flow variables led to several quantitative disagreements with the predictive models that are currently being used. Much of this disagreement appears to have arisen because the electron beam was clipped by apertures inside the accelerator, leading to large fluctuations in beam current during the run. Recent models suggest that, in addition to electron beam loss at these apertures, scattering may have introduced helicity into the trajectory of the electrons in the electron beam, leading to reduced penetration depth.

RESULTS OF THE 1 MW RADIATIVELY-DRIVEN HYPERSONIC WIND TUNNEL EXPERIMENTS

The results of experiments involving the addition of over 800 kW of electron beam power injected into a supersonic air are reported. Using externally applied magnetic fields, a high-energy electron beam was directed and focused into a nozzle sustaining supersonic airflow. The experiments were undertaken to denJonstrate that downstream energy addition could be a viable solution to the limitations on run time and air quality that are encountered by hypersonic ground test facilities. In this work the total enthalpy of the flow was increased by a factor of -3, an amount similar to what will be required for a full scale Mach 12 facility.

Physical Insights on Structure and Reynolds Stress in Turbulent Channel Flow

In this paper we summarize some work in progress on both the statistical characteristics of the near wall turbulent flow in a channel and on the underlying characteristics of the vorticity field, or three -dimensional, ‘coherent’, structures. The work is based on an analysis of a DNS data base provided by Moser et al for channel flows at relatively h igh Re ynolds numbers, up to Re �=950. Emphasis is placed on the vorticity and especially the streamwise vorticity. The statistics obtained from spatial correlations and from velocity -vorticity correlations illuminate the underlying source of streamwise vor ticity, the consequences of the no slip boundary condition and the fact that the array of the regions of streamwise vorticity, which is typically formed, is unstable. The tilting terms which oppose th e loss due to diffusion of the streamwise vorticity are discussed. Simple physical models provide insight into both the behavior of the streamwise vorticity and its connection with the Reynolds stress.