DNS of Turbulent Heat Transfer in Impinging Jets at Different Reynolds and Prandtl Numbers

The heat transfer between an impinging circular jet and a flat plate is studied by means of direct numerical simulations (DNS) for different Prandtl numbers of the fluid. The thermal field is resolved for Pr= 1, 0.72, 0.025, and 0.01. The flow is incompressible and the temperature is treated as a passive scalar field. The jet originates from a fully developed turbulent pipe flow and impinges perpendicularly on a smooth solid heated plate placed at two pipe diameters distance from the jet exit section. The values of Reynolds numbers based on the pipe diameter and bulk mean velocity in the pipe are set to Re= 5300 and Re= 10000. Inflow boundary conditions are enforced using a precursor simulation. Heat transfer at the wall is addressed through the Nusselt number distribution and main flow field statistics. At fixed Reynolds number it is shown that the Prandtl number influences the intensity of the Nusselt number at a given radial location, and that the Nusselt number distribution along the plate exhibit similar features at different Prandtl numbers. The characteristic secondary peak in the Nusselt number distribution is found for both Reynolds numbers for Pr= 0.025 and Pr = 0.01. All the simulations presented in this study were performed with the high order spectral element code Nek5000. Generated flow field statistics are available in the open access repository KITOpen

The Modeling of unsteady turbulent flows in turbomachines

The suitability of existing models for the simulation of flow through turbomachines is investigated and compared with a recently proposed adaptive turbulence model. Discussed are the improvements in accuracy that can be achieved by using non-linear turbulence models and unsteady calculations. The adaptive turbulence model is based on two equation turbulence modeling. It uses the temporal and spatial scales of the flow field to automatically adapt itself to the unresolved turbulent fluctuations. At its asymptotic limits it reduces either to a Direct Numerical Simulation – when the turbulent scales are in the order of the Kolmogorov micro scale – or to a standard two equation model – when the fluctuations are not resolved at all. In order to compare the quality of the presented models two cases have been considered: the flow past a cylinder and a subsonic as well as transonic flow past the VKI turbine blade. Calculations have been performed for each case using all the models and the results have been compared with measurements. The unsteady calculations gave better agreement with the experimental data demonstrating the superiority over steady state calculations for turbomachines

KAPPA - Karlsruhe parallel program for aerodynamics

Research in fluid dynamics can be done on both an experimental and numerical basis, For the latter a computer code needs to be written in order to solve the governing fluid flow equations. The KAPPA code is a CFD simulation package serving as a platform to develop faster and more accurate numerical schemes, better physical models, or as an engineering tool for the simulations of flows in technical equipment. Another important subject is the training and education of students or engineers. Since CFD is highly calculation intensive, new computer architectures such as vector and parallel computers are necessary to treat more complex flow fields or to resolve these flows more accurately. Therefore KAPPA has been specially designed to be used on these architectures. The structure of the code is such that the solution of additional transport equations needed for the simulation of chemistry, turbulence modeling, multiphase flows etc. can be easily implemented. In order to treat complex geometries the code is block structured. The finite volume method is used to discretize the equations in space. The code is written in Fortran 90 using the highly desirable new feature of this language. For the application of the code on parallel computers a message passing tool has been used

Flow simulation at shock wave triple point

The paper presents supersonic flow simulation results concerning the lambda-foot formation in the divergent nozzle. The SPARC code was used and the vicinity of the triple point was analysed. Special boundary conditions have been used in order to obtain supersonic inlet velocity with shock wave in the divergent nozzle. It was proved that the condition of pressure equality on both sides of shear layer following the triple point for flow parameter of interest, does not hold