Simulation of Supersonic Base Flows: Numerical Investigations Using DNS, LES, and URANS. PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download Simulation of Supersonic Base Flows: Numerical Investigations Using DNS, LES, and URANS. PDF full book. Access full book title Simulation of Supersonic Base Flows: Numerical Investigations Using DNS, LES, and URANS. by . Download full books in PDF and EPUB format.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 342
Get Book Here
Book Description
Transitional and turbulent supersonic axisymmetric wakes were investigated by conducting various numerical experiments. The main objective was to identify hydrodynamic instability mechanisms in the flow at Mach number M = 2.46 for several Reynolds numbers, and relating these to coherent structures that are found from various visualization techniques. The premise for this approach is the assumption that flow instabilities lead to the formation of coherent structures. The effect of these structures on the mean flow is of particular interest, as they strongly affect the base drag. Three high-order accurate compressible codes were developed in cylindrical coordinates for this research: A spatial Navier-Stokes (N-S) code to conduct Direct Numerical Simulations (DNS), a linearized N-S code for linear stability investigations using two-dimensional basic states, and a temporal N-S code for performing local stability analyses. The ability of numerical simulations to deliberately exclude physical effects is exploited. With this approach, the impact of structures associated with certain modes on the global wake-behavior can be scrutinized. It is concluded that azimuthal modes with low wavenumbers are responsible for a flat mean base-pressure distribution and that k=2 and k=4 are the dominant modes in the trailing wake, producing a four-lobe wake pattern. Circumstantial evidence is presented that absolutely unstable global modes within the recirculation region coexist with convectively unstable shear-layer modes. The flow is found to be absolutely unstable with respect to modes k>0 for Re-D> 5,000 and with respect to the axisymmetric mode for Re-D>100,000. Furthermore, it is investigated whether flow control measures designed to weaken the naturally most significant modes can decrease the base drag. Finally, the novel Flow Simulation Methodology (FSM), using state-of-the-art turbulence closures, was shown to reproduce DNS results at a fraction of the computational cost.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 342
Get Book Here
Book Description
Transitional and turbulent supersonic axisymmetric wakes were investigated by conducting various numerical experiments. The main objective was to identify hydrodynamic instability mechanisms in the flow at Mach number M = 2.46 for several Reynolds numbers, and relating these to coherent structures that are found from various visualization techniques. The premise for this approach is the assumption that flow instabilities lead to the formation of coherent structures. The effect of these structures on the mean flow is of particular interest, as they strongly affect the base drag. Three high-order accurate compressible codes were developed in cylindrical coordinates for this research: A spatial Navier-Stokes (N-S) code to conduct Direct Numerical Simulations (DNS), a linearized N-S code for linear stability investigations using two-dimensional basic states, and a temporal N-S code for performing local stability analyses. The ability of numerical simulations to deliberately exclude physical effects is exploited. With this approach, the impact of structures associated with certain modes on the global wake-behavior can be scrutinized. It is concluded that azimuthal modes with low wavenumbers are responsible for a flat mean base-pressure distribution and that k=2 and k=4 are the dominant modes in the trailing wake, producing a four-lobe wake pattern. Circumstantial evidence is presented that absolutely unstable global modes within the recirculation region coexist with convectively unstable shear-layer modes. The flow is found to be absolutely unstable with respect to modes k>0 for Re-D> 5,000 and with respect to the axisymmetric mode for Re-D>100,000. Furthermore, it is investigated whether flow control measures designed to weaken the naturally most significant modes can decrease the base drag. Finally, the novel Flow Simulation Methodology (FSM), using state-of-the-art turbulence closures, was shown to reproduce DNS results at a fraction of the computational cost.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Get Book Here
Book Description
Direct Numerical Simulations (DNS) of supersonic flow over a flat-plate with and without adverse pressure-gradient at Mach 3 were carried out in close collaboration with the experimental effort at Princeton University by G. Brown and co-workers. To confirm that simulations and experiments were based on the same "baseflow," the experimental baseflow profiles were compared with our Navier-Stokes results. The downstream development and the spatial growth rates of the disturbances obtained from the Navier-Stokes computations and from experimental measurements were compared as well. Overall, a remarkably good agreement was achieved. Towards the understanding of the nonlinear mechanisms, we investigated numerous nonlinear resonance and breakdown scenarios. Our simulations have shown that due to the stabilizing effects of compressibility for supersonic boundary layers, the transition process can be stretched significantly in the downstream direction and sometimes the transition process may even be aborted so that a turbulent boundary layer is never fully established. The extent of the transition process and the intensity of the temperature fluctuations, and the resulting heat load, depend strongly on the nonlinear mechanisms.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Get Book Here
Book Description
Direct Numerical Simulations (DNS) of supersonic flow over a flat-plate with and without adverse pressure-gradient at Mach 3 were carried out in close collaboration with the experimental effort at Princeton University by G. Brown and co-workers. To confirm that simulations and experiments were based on the same "baseflow," the experimental baseflow profiles were compared with our Navier-Stokes results. The downstream development and the spatial growth rates of the disturbances obtained from the Navier-Stokes computations and from experimental measurements were compared as well. Overall, a remarkably good agreement was achieved. Towards the understanding of the nonlinear mechanisms, we investigated numerous nonlinear resonance and breakdown scenarios. Our simulations have shown that due to the stabilizing effects of compressibility for supersonic boundary layers, the transition process can be stretched significantly in the downstream direction and sometimes the transition process may even be aborted so that a turbulent boundary layer is never fully established. The extent of the transition process and the intensity of the temperature fluctuations, and the resulting heat load, depend strongly on the nonlinear mechanisms.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 116
Get Book Here
Book Description
A new compressible Navier-Stokes code in cylindrical coordinates was developed for investigating axisymmetric wakes of bluff-based bodies in supersonic flows. In this code, high-order compact finite differences derived for non-equidistant grids are employed and a new stare-of-the-art axis treatment is incorporated. Additionally, the fully three-dimensional transport equations for turbulent kinetic energy and turbulent dissipation are implemented to enable (steady or unsteady) Reynolds Averaged Navier Stokes (RANS) simulations. Furthermore, a new "Flow Simulation Methodology" (FSM) was developed for computing complex compressible flows. The centerpiece of FSM) is a strategy to provide the proper amount of modeling of the subgrid scales. This is accomplished by a "contribution function" which locally and instantaneously compares the smallest relevant scales to the local grid size. The contribution function is designed such that it provides no modeling if the computation is locally well resolved so that the computation approaches a Direct Numerical Simulation (DNS) in the fine grid limit, or provides modeling of all scales in the coarse grid limit and thus approaches an unsteady PANS (URANS) calculation. In between these resolution limits, the contribution function adjusts the necessary modeling for the unresolved scales while the larger (resolved) scales are computed as in traditional Large Eddy Simulations (LES) . Preliminary results have shown that the new high- order code has great advantages for supersonic base flow simulations and that calculations, in particular together with FSM), will allow simulations of supersonic base flows at much higher Reynolds numbers than possible with conventional LES.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Get Book Here
Book Description
A zonal, implicit, time-marching Navier-Stokes computational technique has been used to compute the turbulent supersonic base flow over a cylindrical afterbody with base bleed. A critical element of calculating such flows is the turbulence model. Two eddy viscosity turbulence models have been used in the base region flow computations. These models include an algebraic turbulence model and a two-equation k-e model. The k-e equations are solved using an implicit algorithm, and calculations with the k-e model are extended up to the wall. Flow field computations have been performed for a cylindrical afterbody at M approx. = 2.46 and at an angle of attack of a = 0. The results are compared to the experimental data for the same conditions and the same configuration. Details of the mean flow field as well as the turbulence quantities have been presented. In addition, the computed base pressure distribution has been compared with the experiment. In general, the k-e turbulence model performs better in the near wake than the algebraic model and predicts the base pressure much better.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 40
Get Book Here
Book Description
A zonal, implicit, time-marching Navier-Stokes computational technique has been used to compute the turbulent supersonic base flow over a cylindrical afterbody with base bleed. A critical element of calculating such flows is the turbulence model. Two eddy viscosity turbulence models have been used in the base region flow computations. These models include an algebraic turbulence model and a two-equation k-e model. The k-e equations are solved using an implicit algorithm, and calculations with the k-e model are extended up to the wall. Flow field computations have been performed for a cylindrical afterbody at M approx. = 2.46 and at an angle of attack of a = 0. The results are compared to the experimental data for the same conditions and the same configuration. Details of the mean flow field as well as the turbulence quantities have been presented. In addition, the computed base pressure distribution has been compared with the experiment. In general, the k-e turbulence model performs better in the near wake than the algebraic model and predicts the base pressure much better.
Author: George D. Catalano
Publisher:
ISBN: 9781423550181
Category :
Languages : en
Pages : 62
Get Book Here
Book Description
A computational fluid dynamics (CFD) approach to predicting high- speed aerodynamic flow fields of interest to the U.S. Army Research Laboratory (ARL) has been carried out The aerodynamic problems of particular interest are: (1) supersonic flow past the aftbody of projectiles with base mass injection, (2) supersonic flow past the M549 projectile, and (3) subsonic, transonic, and supersonic flow past an M864 projectile with base bleed and wake combustion. The commercially available FLUENT (Fluent, Inc. FLUENT. Version 5.1.1, Lebanon, NH, 1999.) CFD code was utilized. The computational effort supports an ongoing ARL- sponsored experimental investigation. Of particular interest in the present investigation is the careful characterization of the various turbulence models employed in the CFD code. Additionally, the ease of use and set-up as well as the computational time will be described. An experimental effort (Dutton, J. C., and A. L. Addy. 'Fluid Dynamic Mechanisms and Interactions Within Separated Flows'. U.S. Army Research Office Research Grant DAAH04-93-G-0226 and the Department of Mechanical and Industrial Engineering, University of illinois, Urbana-Champagne, Urbana, IL, August 1998.) consisting of detailed laser Doppler velocimeter (LDV), particle image velocimeter (PIV), and high-speed wall pressure measurements has been made in axisymmetric and planar subsonic and supersonic flows with embedded separated regions. The present work seeks to predict similar flow fields computationally and to address areas of agreement and disagreement.
Author: Gary Alan Sullins
Publisher:
ISBN:
Category :
Languages : en
Pages : 178
Get Book Here
Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Get Book Here
Book Description
A zonal, implicit, time-marching Navier-Stokes computational technique has been used to compute the turbulent supersonic base flow over cylindrical afterbodies. A critical element of calculating such flows is the turbulence model. Various eddy viscosity turbulence models have been used in the base region flow computations. These models include two algebraic turbulence models and a two-equation k-epsilon model. The k-epsilon equations are developed in a general coordinate system and solved using an implicit algorithm. Calculations with the k-epsilon model are extended up to the wall. Flow field computations have been performed for a cylindrical afterbody at M = 2.46 and at angle of attack alpha = 0. The results are compared to the experimental data for the same conditions and the same configuration. Details of the mean flow field as well as the turbulence quantifies have been presented. In addition, the computed base pressure distribution has been compared with the experiment. In general, the k-epsilon turbulence model performs better in the near wake than the algebraic models and predicts the base pressure much better. Base flow, Base pressure, Turbulence models, Wake, Supersonic flow.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
