The effect of incoming organized disturbance and free-stream turbulence on leading-edge heat transfer is investigated numerically. An optimum length scale is found to give the maximum heat transfer enhancement for the organized disturbance case. Beyond this optimum value, the enhancement decreases with the increase of length scale. For the free-steam turbulence case, large eddy simulation with dynamic SGS model is performed at Reynolds number Re(D) = 10(exp 4) based on upstream velocity...
Topics: DTIC Archive, Lele, Sanjiva K, STANFORD UNIV CA DEPT OF AERONAUTICS AND ASTRONAUTICS, *HEAT...
Numerical comparisons in decaying isotropic turbulence suggest that there exist discrepancies in time correlations evaluated by DNS and LES using eddy-viscosity-type SGS models. This is consistent with the previous observations in forced isotropic turbulence. Therefore, forcing is not the main cause of the discrepancies. Comparisons among different SGS models in the LES also indicate that the model choice affects the time correlations in the LES. The multi-scale LES method using the dynamic...
Topics: NASA Technical Reports Server (NTRS), LARGE EDDY SIMULATION, SPACE-TIME FUNCTIONS, DIRECT NUMERICAL...
The structure of the two-point spatial correlations (velocity-velocity, velocity-scalar, and scalar-scalar) were studied with a view to improve turbulence closure models. The linear model for the two-point correlations proposed by Naot provides a method of including the information about the turbulence structure in the turbulence models. The assumptions and adequacy of this model were tested against the homogeneous shear flow simulation data base. The model performs poorly in some details and...
Topics: NASA Technical Reports Server (NTRS), COMPUTATIONAL FLUID DYNAMICS, HOMOGENEOUS TURBULENCE,...
Sound radiated by turbulent flow is dependent on the space-time characteristics of the flow field. According to Lighthill's theory (Lighthill 1952; Proudman 1952), acoustic power spectra in the far-fields are determined by the two-time, two-point Eulerian velocity correlations. This has significant implications to the use of large eddy simulation (LES) for aerodynamic noise prediction. The existing subgrid scale (SGS) models are mostly constructed to predict spatial statistics such as energy...
Topics: DTIC Archive, He, Guo-Wei, Wang, Meng, Lele, Sanjiva K., CHINESE ACADEMY OF SCIENCES BEIJING INST...
Stagnation point flow and heat transfer under free-stream turbulence was studied. A new code and an optimized scheme were developed for this study. The optimized scheme was found to significantly save the computational cost. In addition, methods for prescribing realistic inflow turbulence were developed. Simulations with organized inflow disturbances were conducted to study the effect of spanwise length scale and intensity on the enhancement of wall heat transfer and skin friction. Three...
Topics: DTIC Archive, Lele, Sanjiva K., STANFORD UNIV CA DEPT OF MECHANICAL ENGINEERING, *HEAT TRANSFER,...
Funds were received in April 2001 under the Department of Defense DURIP program for construction of a 48 processor high performance computing cluster. This report details the hardware which was purchased and how it has been used to enable and enhance research activities directly supported by, and of interest to, the Air Force Office of Scientific Research and the Department of Defense. The report is divided into two major sections. The first section after this summary describes the computer...
Topics: DTIC Archive, Lele, Sanjiva K, STANFORD UNIV CA DEPT OF AERONAUTICS AND ASTRONAUTICS, *AERODYNAMIC...
Current methods for predicting the noise of high speed jets are largely empirical. These empirical methods are based on the jet noise data gathered by varying primarily the jet flow speed, and jet temperature for a fixed nozzle geometry. Efforts have been made to correlate the noise data of co-annular (multi-stream) jets and for the changes associated with the forward flight within these empirical correlations. But ultimately these emipirical methods fail to provide suitable guidance in the...
Topics: NASA Technical Reports Server (NTRS), LARGE EDDY SIMULATION, NOISE PREDICTION, NOZZLE DESIGN,...
A thorough investigation of leading edge heat transfer on a model geometry has been performed using Large-eddy simulation (LES). with support from the current and a previous AFOSR grant. The results from the leading edge study are presented as a detailed Appendix in this report. To address the problem of solving the full three-dimensional turbulent flow in a turbine passage. including the effects of free-stream turbulence from the combustor, and the unsteady interactions between various blade...
Topics: DTIC Archive, Lele, Sanjiva K, STANFORD UNIV CA, *HEAT TRANSFER, *TURBULENCE, *TURBULENT FLOW,...
Direct numerical simulations of compressible free shear layers in open domains are conducted. Compact finite-difference schemes of spectral-like accuracy are used for the simulations. Both temporally-growing and spatially-growing mixing layers are studied. The effect of intrinsic compressibility on the evolution of vortices is studied. The use of convective Mach number is validated. Details of vortex roll up and pairing are studied. Acoustic radiation from vortex roll up, pairing and shape...
Topics: NASA Technical Reports Server (NTRS), COMPRESSIBLE FLOW, FINITE DIFFERENCE THEORY, FREE FLOW,...
