LES-based evaluation of a microjet noise reduction concept in static and flight conditions

AbstractThe Large-Eddy Simulation (LES) numerical system established since 2002 for jet-noise computation is first evaluated in terms of recent gains in accuracy with increased computer resources, and is then used to explore the relatively new “microjet” noisereduction concept (injection of high-pressure microjets in the vicinity of the main jet nozzle exit), which currently attracts significant attention in the aeroacoustic community. The simulations are found to capture the essential features of the flow/turbulence and the far-field noise alteration by the microjets observed in experiments, and to reveal the subtle flow features responsible for the effect of injection on noise. They also confirm the experimental observation that in static conditions microjets provide a noise reduction comparable with that from chevrons in the low-frequency range, and probably have a less pronounced high-frequency penalty. This positive evaluation of the microjets concept is, however, mitigated by results of simulations in flight conditions, which were never studied experimentally. The latter results, which are awaiting an experimental verification, make a practical use of the concept in its current form rather unlikely

Reynolds-Averaged Navier-Stokes Analysis of Zero Efflux Flow Control over a Hump Model

The unsteady flow over a hump model with zero efflux oscillatory flow control is modeled computationally using the unsteady Reynolds-averaged Navier-Stokes equations. Three different turbulence models produce similar results, and do a reasonably good job predicting the general character of the unsteady surface pressure coefficients during the forced cycle. However, the turbulent shear stresses are underpredicted in magnitude inside the separation bubble, and the computed results predict too large a (mean) separation bubble compared with experiment. These missed predictions are consistent with earlier steady-state results using no-flow-control and steady suction, from a 2004 CFD validation workshop for synthetic jets

Simulation of a Shear Coaxial GO2/GH2 Rocket Injector with DES and LES Using Flamelet Models

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97098/1/AIAA2012-3744.pd

Detached-Eddy Simulation of the Vortical Flowfield about the VFE-2 DeltaWing

The numerical simulation of the flow around a 65° delta wing configuration with rounded leading edges is presented. For the numerical simulation the Cobalt Code uses a cell-centered unstructured hybrid mesh approach. Several numerical results are presented for the steady RANS equations as well as for DES and DDES hybrid approaches. The simulations are done as part of the NATO RTO/AVT 113 working group focusing on experimental and numerical research on delta wing configurations with rounded leading edges. Within this paper the focus is related to the dual primary vortex flow topology, especially the sensitivity of the flow to angle of attack and Reynolds number effects. Reasonable results are obtained with both steady RANS and SA-DDES simulations. The results are compared and verified by experimental data, including surface pressure and pressure sensitive paint results. The impact of transition is assessed, and recommendations for improving future simulations are made

Numerical Study Comparing RANS and LES Approaches on a Circulation Control Airfoil

A numerical study over a nominally two-dimensional circulation control airfoil is performed using a large-eddy simulation code and two Reynolds-averaged Navier-Stokes codes. Different Coanda jet blowing conditions are investigated. In addition to investigating the influence of grid density, a comparison is made between incompressible and compressible flow solvers. The incompressible equations are found to yield negligible differences from the compressible equations up to at least a jet exit Mach number of 0.64. The effects of different turbulence models are also studied. Models that do not account for streamline curvature effects tend to predict jet separation from the Coanda surface too late, and can produce non-physical solutions at high blowing rates. Three different turbulence models that account for streamline curvature are compared with each other and with large eddy simulation solutions. All three models are found to predict the Coanda jet separation location reasonably well, but one of the models predicts specific flow field details near the Coanda surface prior to separation much better than the other two. All Reynolds-averaged Navier-Stokes computations produce higher circulation than large eddy simulation computations, with different stagnation point location and greater flow acceleration around the nose onto the upper surface. The precise reasons for the higher circulation are not clear, although it is not solely a function of predicting the jet separation location correctly

Comparison of RANS, DES and DDES Results for ONERA M-6 Wing at Transonic Flow Speed Using an In-House Parallel Code

The very first thought that comes to the mind with the application area of the DES and DDES schemes is a massively separated flow with highly unsteady flowfield. However, for various complex three dimensional cases, there is no prior knowledge of the flowfield in the domain and it may have mild separation or no separation at all with a steady domain. This study is carried out to see that what will be the behaviour of the DES and DDES schemes in comparison with the URANS scheme if they are applied to a steady state case. An in-house mpi code DG-DES is used for the present study. Three different flux computational schemes named Roe, AUSM and HLLC schemes within DES formulation are compared to check the response for the flows without massive separation and unsteadiness. The cases are run in both single and double precision mode for DES formulation using Roe flux computational scheme to appreciate the accuracy of the solver. A good comparison of pressure distribution with the experimental data is obtained for all URANS, DES and DDES simulations. The pressure distribution results for DES scheme using single and double precision agree well with the experimental data. The pressure distribution predicted by DES using Roe, AUSM and HLLC schemes agree well with the experimental data. The computed values of Cl and Cd are also in close approximity to the other studies. The drag predicted by all DES and DDES simulations is lower than the URANS scheme. It indicates that the DES and DDES schemes generate lower dissipation due to switching to the LES mode and hence result in lower drag prediction as compared with the URANS solution. There is no anomaly observed in the flow due to the use of DES or DDES for steady flow case

The Lag Model Applied to High Speed Flows

The Lag model has shown great promise in prediction of low speed and transonic separations. The predictions of the model, along with other models (Spalart-Allmaras and Menter SST) are assessed for various high speed flowfields. In addition to skin friction and separation predictions, the prediction of heat transfer are compared among these models, and some fundamental building block flowfields, are investigated

Drag Prediction Using Adaptive Discontinuous Finite Elements

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106502/1/AIAA2013-51.pd

Long Hole Film Cooling Dataset for CFD Development - Flow and Film Effectiveness

An experiment investigating flow and heat transfer of long (length to diameter ratio of 18) cylindrical film cooling holes has been completed. In this paper, the thermal field in the flow and on the surface of the film cooled flat plate is presented for nominal freestream turbulence intensities of 1.5 and 8 percent. The holes are inclined at 30 deg above the downstream direction, injecting chilled air of density ratio 1.0 onto the surface of a flat plate. The diameter of the hole is 0.75 in. (approx. 0.02 m) with center to center spacing (pitch) of 3 hole diameters. Coolant was injected into the mainstream flow at nominal blowing ratios of 0.5, 1.0, 1.5, and 2.0. The Reynolds number of the freestream was approximately 11,000 based on hole diameter. Thermocouple surveys were used to characterize the thermal field. Infrared thermography was used to determine the adiabatic film effectiveness on the plate. Hotwire anemometry was used to provide flowfield physics and turbulence measurements. The results are compared to existing data in the literature. The aim of this work is to produce a benchmark dataset for Computational Fluid Dynamics (CFD) development to eliminate the effects of hole length to diameter ratio and to improve resolution in the near-hole region. In this report, a Time Filtered Navier Stokes (TFNS), also known as Partially Resolved Navier Stokes (PRNS), method that was implemented in the Glenn-HT code is used to model coolant-mainstream interaction. This method is a high fidelity unsteady method that aims to represent large scale flow features and mixing more accurately

Development of one-equation transition/turbulence models

This paper reports on the development of a unified one-equation model for the prediction of transitional and turbulent flows. An eddy viscosity--transport equation for nonturbulent fluctuation growth based on that proposed by Warren and Hassan is combined with the Spalart-Allmaras one-equation model for turbulent fluctuation growth. Blending of the two equations is accomplished through a multidimensional intermittency function based on the work of Dhawan and Narasimha. The model predicts both the onset and extent of transition. Low-speed test cases include transitional flow over a flat plate, a single element airfoil, and a multi-element airfoil in landing configuration. High-speed test cases include transitional Mach 3.5 flow over a 5{degree} cone and Mach 6 flow over a flared-cone configuration. Results are compared with experimental data, and the grid-dependence of selected predictions is analyzed