Mohammad Shoeybi

On the use of the Ffowcs Williams-Hawkings equation to predict far-field jet noise from large-eddy simulations

This study presents best practices for the use of the permeable-surface Ffowcs Williams-Hawkings equations to calculate far-field sound from large-eddy simulations of high-speed turbulent jets. A parametric study of the Ffowcs Williams-Hawkings equations is performed by post-processing existing large-eddy simulations at different operating conditions gathering subsonic, supersonic, cold, isothermal, and heated jets. It is concluded that using the pressure formulations of the Ffowcs Williams-Hawkings equations yields better results than the density formulation, especially for the heated jet. In terms of surface closure, best results are obtained with closed surfaces, in conjunction with outflow disk averaging, which confirms the results obtained by Spalart and Shur in 2009. This is different from most previous studies, which recommend using open surfaces. In addition, detailed implementation information and quantified technical recommendations are presented as a guideline for post-processing large-eddy simulations for jet noise.

Large-Eddy Simulations of Perfectly Expanded Supersonic Jets Using an Unstructured Solver

Large-eddy simulations of supersonic jets are performed to validate the development of a second-order finite volume unstructured solver for aeroacoustic applications. Two supersonic jets issuing from an axisymmetric nozzle at Mach number 1.4 are computed: one unheated jet with a Reynolds number of 150,000 and one heated jet with a Reynolds number of 76,000 and a temperature ratio of 1.75. Flow and noise results are compared with the experimental database fromNASAGlennResearchCenter. The nozzle is included in the computational domain.The present study shows that the results from the unstructured solver are in good agreement with the experimental data for time-averaged and fluctuating quantities, velocity spectra in the jet, and the sound obtained in the near field and the far field using the integration of the Ffowcs–Williams and Hawkings equation.

An adaptive implicit-explicit scheme for the DNS and LES of compressible flows on unstructured grids

An adaptive implicit-explicit scheme for Direct Numerical Simulation (DNS) and Large-Eddy Simulation (LES) of compressible turbulent flows on unstructured grids is developed. The method uses a node-based finite-volume discretization with Summation-by-Parts (SBP) property, which, in conjunction with Simultaneous Approximation Terms (SAT) for imposing boundary conditions, leads to a linearly stable semi-discrete scheme. The solution is marched in time using an Implicit-Explicit Runge-Kutta (IMEX-RK) time-advancement scheme. A novel adaptive algorithm for splitting the system into implicit and explicit sets is developed. The method is validated using several canonical laminar and turbulent flows. Load balance for the new scheme is achieved by a dual-constraint, domain decomposition algorithm. The scalability and computational efficiency of the method is investigated, and memory savings compared with a fully implicit method is demonstrated. A notable reduction of computational costs compared to both fully implicit and fully explicit schemes is observed.

Numerical Investigation of the Acoustic Behavior of a Multi-perforated Liner

The acoustic response of a turbulent flow through a multi-perforated liner is computed with incompressible LES. The effect of a large array of apertures is accounted for by simulating a single jet with periodic conditions in both directions tangential to the plate. Flows that are parallel to the plate are included in the regions above and below the aperture, which is tilted in the tangential flow direction as in practical film cooling liners. The mass flow rate through the aperture is forced with a small sinusoidal perturbation superposed on a mean component. The acoustic behavior is determined by measuring the fluctuating pressure difference across the aperture that results from the forcing. In this work, two different forcing frequencies are considered. The transfer function between forcing and response, which represents the acoustic impedance of the liner, is calculated for these frequencies. Good agreement is found when compared with existing theory, when the latter is modified for the thickness and tilting of the aperture.

Noise Prediction from Cold High-Speed Turbulent Jets Using Large-Eddy Simulation

A flexible hybrid approach is investigated for computing far-field jet noise. Compressible large eddy simulation based on a linear discontinuous Galerkin (DG) solver is used to com- pute the near-field flow. The far-field noise is computed using a Ffowcs Williams-Hawkings solver. Two variants for the degrees of freedom in the linear DG solver are considered and their impact on the implicit numerical dissipation tested. Both variants support arbitrary, approximately convex polyhedral elements. The overall method is applied to predict the far-field noise of a Ma = 0.9 cold turbulent jet including nozzle geometry. Comparisons with measured flow fields are reasonable, however preliminary noise predictions show excessive falloff in the high frequency range.