A. Hamed

Erosion study of different materials affected by coal ash particles

Abstract Alloys in contact with coal particles or coal ash are exposed to erosion. The problem of predicting erosion is very complex. The present paper describes he test facility which is designed in such a way that the aerodynamic effects are an integral part of the erosion test parameters. Some results from the alloys studied (aluminum, stainless steel and titanium) in this investigation are reported.

Turbine Blade Surface Deterioration by Erosion

This paper presents the results of a combined experimental and computational research program to investigate turbine vane and blade material surface deterioration caused by solid particle impacts. Tests are conducted in the erosion wind tunnel for coated and uncoated blade materials at various impact conditions. Surface roughness measurements obtained prior and subsequent to the erosion tests are used to characterize the change in roughness caused by erosion. Numerical simulations for the three-dimensional flow field and particle trajectories through a low-pressure gas turbine are employed to determine the particle impact conditions with stator vanes and rotor blades using experimentally based particle restitution models. Experimental results are presented for the measured blade material/coating erosion and surface roughness. The measurements indicate that both erosion and surface roughness increase with impact angle and particle size. Computational results are presented for the particle trajectories through the first stage of a low-pressure turbine of a high bypass turbofan engine. The trajectories indicate that the particles impact the vane pressure surface and the aft part of the suction surface. The impacts reduce the particle momentum through the stator but increase it through the rotor. Vane and blade surface erosion patterns are predicted based on the computed trajectories and the experimentally measured blade coating erosion characteristics.

DETACHED EDDY SIMULATIONS OF SUPERSONIC FLOW OVER CAVITY

Detached Eddy Simulations are performed for unsteady three-dimensional supersonic turbulent flow over an open L/D = 5 cavity at free-stream Mach number of 1.19. Numerical results are obtained from the explicit solution and Shear-Stress-Transport based simulations using the 3 rd order Roe scheme. Computational results are presented for the unsteady vortex and shock structures. The acoustic response of the cavity is presented in the form of pressure fluctuations and sound pressure level spectra. The computational results are compared to existing experimental data and to results obtained from twodimensional Reynolds Averaged Navier Stokes with algebraic turbulence model.

DES and Hybrid RANS/LES models for unsteady separated turbulent flow predictions

This paper proposes two DES (Detached Eddy Simulation) model and one hybrid RANS (Reynolds Averaged Navier -Stokes)/ LES (Large Eddy Simulation) model for the simulations of unsteady separated turbulent f lows. The two -equation k -� based models are implemented in a full 3 -D Navier Stokes solver and simulations are carried out using a 3 rd order Roe scheme. The predictions of the models are compared for a benchmark problem involving transonic flow over an ope n cavity and the equivalence between the DES formulations and the hybrid formulation is established. Predicted results for the vorticity, pressure fluctuations, SPL (Sound Pressure level) spectra and different turbulent quantities; such as modeled and reso lved TKE (Turbulent Kinetic Energy) profiles, contours and spectra are presented to evaluate various aspects of the proposed models. The numerical results for the SPL spectra are compared with available experimental results and also with the prediction fro m LES simulations. The grid resolved TKE profiles are also compared with the LES predictions. A comparative study of the CPU time required for the two DES models and the hybrid model is also made.

DES, HYBRID RANS/LES AND PANS MODELS FOR UNSTEADY SEPARATED TURBULENT FLOW SIMULATIONS

This paper presents computational results for two DES (Detached Eddy Simulation), one hybrid RANS (Reynolds Averaged Navier-Stokes)/ LES (Large Eddy Simulation) and some preliminary results from PANS (Partially Averaged Navier-Stokes) turbulence for simulation of unsteady separated turbulent flows. The models are implemented in a full 3-D Navier Stokes solver and are based on the twoequation k-e model. The formulations of each model are presented and results are analyzed for subsonic flow over a Backward Facing Step (BFS). Simulations are carried out using a 3 rd order Roe scheme. A comparative assessment is made between the predictions from the DES, hybrid and PANS models. The predicted results are compared with the available experimental data for skin-friction coefficient, and different turbulent quantities. The three-dimensionality of the flow field and the separated fine scale structures are presented through the Q iso-surfaces.

Numerical simulations of ice droplet trajectories and collection efficiency on aero - engine rotating machinery

This paper presents a methodology for three dimensional numerical simulations of super cooled water droplet trajectories through aeroengine rotating mac hinery. Both flow and droplets’ governing equations are formulated and solved in the reference frame of rotating blades. A Eulerian -Lagrangian approach is used for the continuous and discrete phases with one -way interaction model to simulate the aerodynami c effects on the three -dimensional particle trajectories. A flux -based collection efficiency model is proposed for internal flows to enable the calculation of the amount of water that impinges the rotating and stationary blade surfaces. The methodology is applied to a transonic fan rotor and the computational results for the 3D flow field is compared with available experimental data. The computed droplet trajectories, rotor blade impingement locations, and the corresponding water collection efficiency are p resented and compared for different droplet sizes.

Flow characteristics in boundary layer bleed slots with plenum

Numerical simulations were conducted to investigate the performance characteristics of bleed through normal slots and its effect on the turbulent boundary layer development under zero and strong adverse pressure gradient caused by incident oblique shock. The solution to the compressible Navier-Stokes and k-epsilon equations was obtained in a domain that includes the regions inside the bleed slot and plenum in addition to the external flow. The computational results demonstrate the interactions between the plenum and bleed flow and the effect of incident shock on the boundary layer development downstream. The computed results agree with the experimentally measured pitot and static pressure distribution inside the slot. The bleed mass flow without incident shock was underpredicted over the range of plenum pressures. The computations predicted the measured increase in bleed mass flow with incident shock.

Particle Dynamics Simulations in Inlet Separator with an Experimentally Based Bounce Model

This article presents a probabilistic simulation methodology for the particle dynamics through a helicopter engines inlet separator with an experimentall y based particle bounce model. The flowfield is determined from the numerical solution of the compressible Navier-Stokes equations with a two-equation turbulence model. The probabilistic simulations of the particle dynamics take into consideration the experimentally measured variance in the particle bounce conditions after surface interactions. Results are presented for the particle trajectories through the inlet and for the separator effectiveness over a range of sand particle sizes, and also for C-spec. sand.

Investigation of gas particle flow in an erosion wind tunnel

Abstract Trajectories of small particles approaching the test specimen in an erosion tunnel are analytically determined. The two-dimensional equations of motion are solved for a spherical particle under the sole influence of aerodynamic drag. The two-dimensional gradients of gas properties in the flow field are determined by a numerical solution of the equations describing a compressible inviscid fluid. At one inlet condition, the trajectories are computed for coal ash particles of various sizes approaching test specimens at several orientations. Trends are identified in the approaching characteristics that may be related to the observed erosion. The results indicate that, for ash particles with diameters less than 10 μm, significant numbers are deflected away from the specimen. These particles would otherwise impact with the specimen if they had more inertia to resist the turning effect of the flow field. Ash particles with diameters less than 30 μm which do impact with the specimen do so over a wide range of incident angles quite different from the angle between the specimen surface and the tunnel axis and at lower velocities than those at the test section inlet. The importance of fluid mechanics in erosion studies is presented in this paper.

High-Temperature Coatings for Protection Against Turbine Deterioration

In this research, an investigation was conducted to study the fly ash particles associated with the erosion behavior of alloys and coatings that are widely used in gas and steam turbines. The erosion behavior of many alloys and protective coatings has been investigated experimentally at high temperatures using a specially designed wind erosion tunnel. The erosion results show the effect of velocity, temperature, and impact angle on the erosion rate.