Showing papers by "Parviz Moin published in 2011"

Unstructured Large Eddy Simulation for Prediction of Noise Issued from Turbulent Jets in Various Configurations

Abstract: A novel numerical scheme for unstructured compressible large eddy simulation (LES) is developed. This method is low-dissipative and less sensitive to the quality of the computational grid and is targeted for performing large-scale, high-fidelity simulations of turbulent flows in complex configurations. The objective of this work is to introduce this method, present a rigorous validation study, and demonstrate the application to a variety of jet configurations. This technique is validated by predicting the flow and noise emitted from a single-stream pressure-matched hot supersonic jet. Nearfield flow as well as farfield noise computed using an acoustic projection method is studied and compared to experimental measurements obtained by Dr. James Bridges at NASA Glenn. Mesh refinement studies and sensitivity study on selecting the acoustic projection surface are provided. To test the method’s performance in a variety of jet noise configurations, it is applied to a high bypass ratio dual-stream jet at sonic conditions, a vertical supersonic jet impinging on the ground, and a horizontal supersonic jet impinging on an angled jet blast deflector.

Noise Prediction of Pressure-Mismatched Jets Using Unstructured Large Eddy Simulation

Abstract: It is our premise that significant new advances in the understanding of noise generation mechanisms for jets and realistic methods for reducing this noise can be developed by exploiting high-fidelity computational fluid dynamics: namely large eddy simulation (LES). In LES, the important energy-containing structures in the flow are resolved explicitly, resulting in a time-dependent, three-dimensional realization of the turbulent flow. In the context of LES, the unsteady flow occurring in the jet plume (and its associated sound) can be accurately predicted without resort to adjustable empirical models. In such a framework, the nozzle geometry can be included to directly influence the turbulent flow including its coherent and fine-scale motions. The effects of propulsion system design choices and issues of integration with the airframe can also be logically addressed.Copyright © 2011 by ASME

A dynamic eddy-viscosity model based on the invariants of the rate-of-strain

Abstract: Large-eddy simulation (LES) seeks to predict the dynamics of spatially filtered turbulent flows. By construction, the LES solution contains only scales of size ≥ ∆, where ∆ denotes some user-chosen length scale of the spatial filter. A large-eddy simulation based on an eddy-viscosity model and a Navier-Stokes simulation differ only in diffusion coefficient. Therefore, we focus on the question: “When does eddy diffusivity reduce a turbulent flow to eddies of size ≥ ∆?”. It is deduced that the eddy viscosity νe has to depend on the two invariants q and r of the filtered rate-of-strain tensor. We present a dynamic version of the resultant eddy-viscosity model and present results from LES of isotropic turbulence and turbulent channel flow.

Spray Modeling and Predictive Simulations in Realistic Gas-Turbine Engines

Abstract: Large-eddy simulation (LES) is a promising technique for accurate prediction of reacting multiphase flows in practical gas-turbine engines. These combustors involve complex physical phenomena of primary atomization of liquid sheet/jet and secondary breakup, droplet evaporation, turbulent mixing of fuel vapor with oxidizer, and combustion dynamics. This chapter summarizes advances made in modeling spray fields with LES of turbulent reacting flows in realistic combustor configurations. Specifically, details of subgrid models for droplet dynamics including breakup, evaporation, deformation, droplet dispersion, and finite-size droplets are presented in the context of an Eulerian–Lagrangian simulation methodology on unstructured grids. Effectiveness of LES with advanced spray models in predicting spray behavior in a patternation study of realistic Pratt and Whitney injector is described.

Fundamental and subharmonic transition to turbulence in zero-pressure-gradient flat-plate boundary layers

Abstract: In this fluid dynamics video, recent simulations of transition to turbulence in compressible (M = 0.2), zero-pressure-gradient flat-plate boundary layers triggered by fundamental (Klebanoff K-type) and subharmonic (Herbert H-type) secondary instabilities of Tollmien-Schlichting waves are highlighted.

Preponderance of hairpin vortices detected from very-large-scale, direct numerical simulations of three flat-plate boundary layers

Abstract: We report high-quality flow visualization results obtained from very-large-scale direct numerical simulation (VLS DNS) of three nominally zero-pressure-gradient, smooth, incompressible, flat-plate boundary layers (ZPGFPBLs). The number of grid points is slightly over 1 billion per simulation. In all the three boundary layers, the momentumthickness Reynolds number develops continuously from 80 to approximately 2000. A unique aspect of the present VLS DNS study is its strong connection and remarkable consistency with the large body of classical ZPGFPBL experimental visualization work that began in the late 1950s, peaked in the early 1980s and still somewhat active until this day. Our VLS DNS results demonstrate, beyond reasonable doubt, a preponderance of hairpin vortices in ZPGFPBLs upto momentum-thickness Reynolds number 2000. Based on these results, it is possible to futher explore the kinematics and dynamics of largescale-motion (LSM) and very-large-scale-motion (VLSM) in ZPGFPBLs.