Roger Simpson

Aerodynamics and Hydrodynamics

1989-present, Jack E. Cowling Professor of Aerospace and Ocean Engineering; 1983-1989, Professor, Aerospace and Ocean Engineering Department, Virginia Polytechnic Institute and State University; 1989-2004, Director, VT Stability Wind Tunnel; 1990, Visiting Scientist, NASA-Ames-Stanford; 1990, Visiting Scientist, University Erlangen-Nürnberg, Germany; 1969-1983, Professor, Southern Methodist University; 1976, Visiting Scientist, Max-Planck-Institute für Strümungsforschung, Göttingen, Germany; 1968, Development Engineer, General Electric Company.

2005 Elected President of the AIAA.

ASME Fellow; Founding Fellow of Inst. Diag. Engrs., U.K.; Fellow, AIAA; President, AIAA, 2005-2007.

Unsteady Separated Flow/Dynamic Stall on Maneuvering Bodies

This research area which has been active for over 17 years is devoted to understanding unsteady turbulent separated flows and dynamic stall that occur on rapidly- maneuvering aircraft, missiles, and submarines. Laser and hot-wire anemometer measurements, flow visualization, and force, moment, and pressure measurements are made in a specially-designed unsteady boundary layer wind tunnel and in the 6' x 6' wind tunnel. A new state-of-the-art dynamic pitching, plunging, and rolling apparatus (DyPPiR) has been designed, constructed, and installed in the 6' x 6' tunnel to simulate rapid aircraft and transient submarine motions using large (7') long models. Miniature fiber optics LDA probes for external flow measurements have been developed for mounting inside of wind tunnel models.

Wing/Body Interaction and Flow Control

When a turbulent boundary layer on the fuselage of an aircraft or another vehicle encounters a wing or appendage, a complex horseshoe vortex structure wraps around the wing causing losses in vehicle performance and generating acoustic noise. Using the above-mentioned experimental techniques, the detailed structure of this type flow is being examined. The phenomena generating the noise has been discovered and methods to eliminate it are being examined. High Reynolds number data are available. Recently, a high free-stream turbulence generator has been built to determine the high turbulence effects on the turbulence structure in a 3-D flow around a wing/body junction and thus simulate 3-D flow effects in gas turbines.

Three-Dimensional Turbulent Boundary Layers with Separation

In conjunction with the above research programs, efforts are being made to help develop a physically-based mathematical model for three-dimensional turbulent boundary layers, even with separation. Measurements of flowfields in our lab using laser-Doppler velocimetry, hot-wire anemometry, surface oil-flow visualizations, and surface pressures form detailed data bases for: (1) three-dimensional flow separations on a 6:1 prolate spheroid model at angle of attack, (2) horseshoe vortical separations around a wing/body junction model, (3) vortical separations on the leeside of an axisymmetric 3-D bump, and (4) highly skewed and separated flow through the tip gap of a linear axial compressor cascade. These data bases are used by our students to help develop models and are used by collaborators such as NASA and the EU ERCOFTAC computational groups.

Convective Heat Transfer in Three-Dimensional Turbulent Boundary Layers

While the structure of three-dimensional turbulent boundary layers is not well understood, there is even less knowledge of the 3-D turbulent heat transfer mechanisms. 3-D turbulent boundary layers can produce lower skin friction, turbulent stress, and heat transfer under certain conditions. In conjunction with the above-mentioned research programs, detailed surface heat flux and temperature field measurements are also being made with possible applications to gas turbines.

Related Instrumentation Development

Due to the specialized nature of the new experiments conducted in the above research programs, new state-of-the-art instruments that are not commercially available are developed to make required measurements with sufficient resolution and precision. A miniature 3-velocity-component laser-Doppler velocimeter (Mini3DLDV) half the size of a credit card was developed recently and used inside the axisymmetric bump model to measure within 50 microns of the test wall. A new Comprehensive laser-Doppler velocimeter system has been developed to measure all the terms in the Reynolds Stress Transport equations used for modeling 3-D flows. New efforts for compressible flows are on improved techniques for filtered Rayleigh scattering and laser-induced fluorescence.

Wavy-Wall Three-Dimensional Turbulent Boundary Layer Experiment

Recently a canonical wavy side-wall experiment was developed to examine the effects of alternating spanwise pressure gradients on the turbulent diffusion and stream-wise vorticity generation in this 3-D turbulent boundary layer. CompLDV measurements of all stress transport equation terms downstream of 6 cycles of spanwise pressure gradient waves have revealed information on velocity/pressure gradient correlations that will be available for turbulence modeling.

Rough-wall 2-D and Three-Dimensional Turbulent Boundary Layers

While the turbulence structure of smooth wall three-dimensional turbulent boundary layers is not well understood or modeled, there is even less knowledge of the effects of surface roughness on 3-D flows. Detailed measurements close to the wall among the roughness elements are being made using advanced LDV systems to determine the fundamental flow mechanisms around roughness. The results show large turbulence production just downstream of each element.