Numerical simulations of unsteady complex geometry flows

Numerical simulations have been here carried out for turbulent flows in geometries relevant to electronic systems. These include plane and ribbed channels and a central processor unit (CPU). Turbulent flows are random, three-dimensional and time-dependent. Their physics covers a wide range of time and space scales. When separation and reattachment occur, together with streamline curvature, modelling of these complex flows is further complicated. It is well known that, when simulating unsteady flows, the traditional, steady, linear Reynolds-averaged Navier-Stokes (RANS) models often do not give satisfactory predictions. By contrast, unsteady, non-linear RANS models may perform better. Hence the application of these models is considered here. The non-linear models studied involve explicit algebraic stress and cubic models. The Reynolds Stress Model (RSM) has been also evaluated. Modelling strategies more advanced than RANS, i.e. Large Eddy Simulation (LES) and zonal LES (ZLES), have also been tested. Validation results from URANS, LES and ZLES indicate that the level of agreement of predictions with benchmark data is generally consistent with that gained by the work of others. For the CPU case, flow field and heat transfer predictions from URANS, LES ; and ZLES are compared with measurements. Overall, for the flow field, ZLES and LES are more accurate than URANS. Zonal low Reynolds number URANS models (using a hear wall k-l model) perform better than high Reynolds number models. However, for heat transfer prediction, none of the low Reynolds number models investigated performed well

Numerical simulations of unsteady complex geometry flows

Numerical simulations have been here carried out for turbulent flows in geometries relevant to electronic systems. These include plane and ribbed channels and a central processor unit (CPU). Turbulent flows are random, three-dimensional and time-dependent. Their physics covers a wide range of time and space scales. When separation and reattachment occur, together with streamline curvature, modelling of these complex flows is further complicated. It is well known that, when simulating unsteady flows, the traditional, steady, linear Reynolds-averaged Navier-Stokes (RANS) models often do not give satisfactory predictions. By contrast, unsteady, non-linear RANS models may perform better. Hence the application of these models is considered here. The non-linear models studied involve explicit algebraic stress and cubic models. The Reynolds Stress Model (RSM) has been also evaluated. Modelling strategies more advanced than RANS, i.e. Large Eddy Simulation (LES) and zonal LES (ZLES), have also been tested. Validation results from URANS, LES and ZLES indicate that the level of agreement of predictions with benchmark data is generally consistent with that gained by the work of others. For the CPU case, flow field and heat transfer predictions from URANS, LES ; and ZLES are compared with measurements. Overall, for the flow field, ZLES and LES are more accurate than URANS. Zonal low Reynolds number URANS models (using a hear wall k-l model) perform better than high Reynolds number models. However, for heat transfer prediction, none of the low Reynolds number models investigated performed well.EThOS - Electronic Theses Online ServiceUniversity of Warwick (UoW)GBUnited Kingdo

Low Reynolds number heat transfer prediction employing large eddy simulation for electronics geometrics.

The accurate prediction of convective heat transfer within electronics systems has always been of great importance for the reliability of such systems. Current computational methods based on the Reynolds-Averaged Navier-Stokes equations do not provide reliable predictions due to the inability of current methods to capture complex time dependent flow features. This study investigates the use of time dependent Large Eddy Simulation and hybrid methods to make more reliable thermal predictions. These methods are tested on a heated ribbed channel, a heated cube in an array of cubes and a complex CPU case. A variety of models and methodologies are applied and analysed. It is apparent that the most important scales are the large vortices generated by geometrical features. Due to the low Reynolds number flows found in electronics systems, there is a relatively small range of scales to capture. This gives rise to some unpredictability in model choice and grid resolution, though consistency is much improved over traditional methods. Important sources of error are considered to be problem definition and boundary conditions for which unsteady data is not available. Use of nonlinear models and higher order discretisation did not provide adequate improvements in accuracy for the increase in computational expense. Combining Reynolds-Averaged Navier-Stokes and Implicit Large Eddy Simulation into a hybrid model seems to provide fair reliability when compared to other modelling methods on a range of grid resolutions

Proceedings of the 2004 Workshop on CFD Validation of Synthetic Jets and Turbulent Separation Control

The papers presented here are from the Langley Research Center Workshop on Computational Fluid Dynamics (CFD) Validation of Synthetic Jets and Turbulent Separation Control (nicknamed "CFDVAL2004"), held March 2004 in Williamsburg, Virginia. The goal of the workshop was to bring together an international group of CFD practitioners to assess the current capabilities of different classes of turbulent flow solution methodologies to predict flow fields induced by synthetic jets and separation control geometries. The workshop consisted of three flow-control test cases of varying complexity, and participants could contribute to any number of the cases. Along with their workshop submissions, each participant included a short write-up describing their method for computing the particular case(s). These write-ups are presented as received from the authors with no editing. Descriptions of each of the test cases and experiments are also included