Seminar: Prediction of Turbulent Temperature Fluctuations in Hot Jets

Large-eddy simulations (LES) were used to investigate turbulent temperature fluctuations and turbulent heat flux in hot jets. A high-resolution finite-difference Navier-Stokes solver was used to compute the flow from a 2-inch diameter nozzle. Three different flow conditions of varying jet Mach numbers and temperature ratios, were examined. The LES results showed that the temperature fields behaves similar to the velocity fields, but with a more rapidly spreading mixing layer. Predictions of mean, ui, and fluctuating velocities, uj′, were compared to previously obtained particle image velocimetry data. Predictions of mean, T and fluctuating temperature, T′ were compared to new data obtained using Raman spectroscopy. Very good agreement with experimental data was demonstrated for the individual quantities. This lends confidence that the combined quantity turbulent heat flux, ρu′iT′ is accurately predicted by the LES. The turbulent heat flux was examined and compared to Reynold-averaged Navier-Stokes (RANS) results. The LES and RANS simulations produced very similar results for the radial heat flux. However, the axial heat flux obtained from the LES differed significantly from the RANS result in both structure and magnitude, indicating that the gradient diffusion type model in RANS is inadequate. Finally, the LES data was used to compute the turbulent Prandtl number and verify that a constant value of 0.7 used in the RANS models is a reasonable assumption.

About the Speaker

Dr. DeBonis is a senior aerospace engineer in the Inlets and Nozzles Branch at the NASA Glenn Research Center.  He has over 25 years of experience in the application and development of computational fluid dynamics methods for inlet and nozzle flows.  He is currently specializing in large-eddy simulation of inlet and nozzle flows.  In addition, he serves as the technical lead at NASA Glenn for the Revolutionary Computational Aerosciences research in NASA's Transformational Tools and Technologies Project, and is a member of the NASA Engineering and Safety Center's Aerosciences Technical Discipline Team.  He is an Associate Fellow of the AIAA.  Dr. DeBonis received a B.S. and Ph.D. degrees in Aeronautical and Astronautical Engineering from the Ohio State University and a M.S. degree in Fluid and Thermal Sciences from Case Western Reserve University.  He has authored over 60 research publications in the areas of inlet and nozzle flows, numerical methods and large-eddy simulation.

Hosted by Professor Datta Gaitonde