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Unsteady Shock Wave: Turbulent Boundary Layer Interaction in the Laval Nozzle

Doerffer P., Szulc O., Magagnato F.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2005

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Vol. 9, No 1

115-132

EN

The flow in transonic diffusers and supersonic air intakes often becomes unsteady due to shock wave-boundary layer interaction. Oscillations may be induced by natural separation unsteadiness or forced by boundary conditions. Significant improvements of CFD tools, increased computer resources and the development of experimental methods have again drawn the attention of researchers to this topic. Forced oscillations of a transonic turbulent flow in an asymmetric two-dimensional Laval nozzle have been considered to investigate the problem. A viscous, perfect gas flow was numerically simulated using SPARC, a Reynolds-averaged compressible Navier-Stokes solver, employing a two-equation, eddy viscosity, turbulence closure in the URANS approach. For time-dependent and stationary flow simulations, Mach numbers upstream of the shock between 1.2 and 1.4 were considered. Comparison of computed and experimental data for steady states generally gave acceptable agreement. In the case of forced oscillations, a harmonic pressure variation was prescribed at the exit plane resulting in shock wave motion. Excitation frequencies between 0Hz and 1024Hz were investigated at a constant pressure amplitude. The main result of the work is the relation between the amplitude of shock wave motion and the excitation frequency in the investigated range. Increasing excitation frequency resulted in decreasing amplitude of the shock movement. At high frequencies, a natural mode of shock oscillation (of small amplitude) was observed, which was insensitive to forced excitement.

2

The Modeling of unsteady turbulent flows in turbomachines

Magagnato F.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2001

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Vol. 5, No 4

477-494

EN

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.

3

Numerical investigation of the secondary flow development in turbine cascade

Doerffer P., Rachwalski J., Magagnato F.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2001

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Vol. 5, No 2

165-178

EN

The results represent the first attempt of the numerical analysis of 3-D secondary flows formed in the linear turbine cascade wind tunnel. Numerical simulations were carried out by means of the SPRC code. It was possible to make presented here calculations thanks to the cluster of PC's providing sufficient computational resources. In order to be able to verify the obtained results the case considered is the workshop test case (D.G.Gregory-Smith 1994 Turbomachinery Workshop Test Case No.3 116). It has been shown that the obtained results are in a very good agreement with experiment. It gave confidence in the results and several important conclusions concerning the development of streamwise vortices could be made thanks to the work carried out.

4

Flow simulation at shock wave triple point

Doerffer P., Namieśnik K., Magagnato F.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2001

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Vol. 5, No 4

549-556

EN

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.

5

KAPPA - Karlsruhe Parallel Program for Aerodynamics

Magagnato F.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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1998

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Vol. 2, No 2

215-270

EN

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.