Robert-Zoltán Szász

Proper Orthogonal Decomposition for Experimental Investigation of Flame Instabilities

An experimental investigation of both confined and unconfined flames on a Triple Annular Research Swirler (TARS) is presented. The paper focuses on post-processing techniques aiming at extracting information on the dynamics that are lost through classical statistics approach. POD together with a derived a-posteriori phase averaging procedure successfully reconstructed the dynamics of flames under thermo-acoustic instabilities in the confined case. For unconfined flames, an analysis of the azimuthal modes is performed.

Numerical study of fluidic injection for noise reduction

We investigate the ability of fluidic injection to control the noise of a model gas-turbine nozzle exhaust. The work is conducted using a hybrid method of LES for the flow field and Lighthills acoustic analogy for the acoustic field. The impact of injection on the flow development in terms of coherent structures and characteristic frequencies is evaluated. The main results show that a low momentum ratio fluidic injection can trigger a vortex pairing mechanism, resulting in energy transfer to a sub-harmonic of the jet preferred shedding frequency. This changes the development and structure of the flow. The corresponding acoustic sources are shown to be significantly damped. For large directivity angles, the spectral distribution and reduction of Sound Pressure Level is in good agreement with experiments.

Numerical investigations of the acoustics of a coaxial nozzle

The acoustic field generated by two coaxial jets is studied numerically. The turbulent non-isothermal flow is handled by Large Eddy Simulations (LES) and the acoustical perturbations are treated by solving an inhomogeneous wave equation. The acoustical source is obtained from the instantaneous LES flow field. The computed flow and acoustical fields are compared to measured data. Good agreement between the computed and the measured results has been found.

Flow and Acoustics of a Coaxial Nozzle: a Sensitivity Study to the Inlet Boundary Conditions

The jet noise generated by the high velocity hot stream exhausting from a jet engine represents a major component of the aircraft noise. Reductions in jet noise has been achieved by using high bypass turbo-fan engines. To solve numerically this problem the flow and acoustic fields generated by two coaxial jets are considered. Large Eddy Simulation (LES) is used to handle the non-isothermal turbulent flow field, while for the acoustic field a wave equation with source terms provided by the instantaneous LES is employed. The effects of the inlet boundary conditions on the flow and acoustics are assessed in this paper. A comparison of the computed mean flow field and the SPL with experimental data show excellent agreement at distances of over a few jet diameters downstream of the the jet exit plane. In the proximal part the agreement is less good. However, the discrepancy between the simulations and the experiments is less than the corresponding variations due to the uncertainness in the experimental boundary conditions.

Computations of the Flow around a Wind Turbine: Grid Sensitivity Study and the Influence of Inlet Conditions

The flow around a complete model wind turbine is computed using LES and the immersed boundary method. The influence of inlet velocity profile and turbulence level is evaluated. The inlet velocity profile was found to have major influence in the upper regions of the flow field. The imposed turbulence level had no major influence on the turbulent spectra but its effect is clearly seen on the generated vortices.

Coaxial jet noise prediction: Grid resolution effect on the numerical solution

The flow and acoustic fields that are generated by two coaxial jets are considered. The problem is handled by solving the flow field using Large Eddy Simulation (LES) and the acoustics by a wave equation with source terms provided by the instantaneous LES. The paper is focused on the influence of the grid resolution on the solution accuracy.

Flow and noise investigations of a separate flow exhaust system

A major component of aircraft noise is the jet noise created by the high velocity hot stream exhausting from a jet engine, interacting with itself and with the surrounding cold air. In the present ...

Load and Response Prediction Using Numerical Methods in Acoustic Fatigue

A numerical procedure for load and response prediction in the context of acoustic fatigue is investigated on a model problem. Contrary to design guidelines, where the load needs to be specified (for example, based on experiments), the procedure used herein consists of simulating the load with computational fluid dynamics and then using the simulated load as a load input to a finite element simulation of the exposed structure. The model problem studied is a ramped backward-facing step with a thin aluminum panel fitted downstream of the step, parallel to the flow. The vortices generated in the wake of the step impose a time-varying load on the aluminum panel. The numerical results on the load and response are compared to experimental results. The load is simulated with large-eddy simulations with a wall function. The mean reattachment length, load intensity, and spectrum compare well with the measurements, with the exception of a somewhat overpredicted cutoff frequency. The panel response prediction compare...

An isothermal analysis of curved-vane and flat-vane swirlers for burners

Purpose – One current trend in burner technology is to obtain high efficiency while keeping low levels of NOx emissions. A swirling flow in combustion ensures a fixed position of a compact flame. Therefore, it is necessary to design efficient swirlers. Flow patterns are simulated for the different swirl devices proposed in this work. Two axial-swirlers are studied: one based on curve-vanes consisting of a straight line with an arc of a circle as the trailing edge and the other is the common flat-vanes. The purpose of this paper is to assess the accuracy of different swirl generators using a well-known benchmark test case. Design/methodology/approach – This work deals with modelling the swirler using two approaches: the general purpose Computational fluid dynamics (CFD) solver Ansys-Fluent® and the suite of libraries OpenFOAM® to solve the Reynolds Averaged Navier Stokes equations, showing there is a slight deviation between both approaches. Their performance involves analyzing not only the Swirl number bu...

Proper Orthogonal Decomposition for experimental investigation of swirling flame instabilities

An experimental investigation of both confined and unconfined flames on a Triple Annular Research Swirler (TARS) is presented. The paper focuses on post-processing techniques aiming at extracting information on the dynamics that are lost through classical statistics approach. POD together with a derived a-posteriori phase averaging procedure successfully reconstructed the dynamics of flames under thermo-acoustic instabilities in the confined case. For unconfined flames, an analysis of the azimuthal modes is performed.