Browsing by Author "Tan, S. C."
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Item Open Access Erosion in centrifugal compressor impellers(Cranfield University, 1996-01) Harris, P. K.; Tan, S. C.; Elder, R. L.An experimental and theoretical study of erosion in centrifugal compressor impellers is presented. An experimental rig using laser anemometry techniques was employed to create a database of particle restitution ratios for a range of materials. This data was unique in that the particle rebound was measured in a quiescent condition where the aerodynamic effects had been minimised, and also parametric factors not previously available were included. These values were incorporated into the existing Particle Trajectory Code developed by Cranfield University and Rolls Royce PLC. The code is used to calculate the trajectories of discrete particles in three dimensional gas turbine geometries, and the ensuing erosion. It was modified to include the effects of the periodic boundary conditions, particle fragmentation, splitter blades, and variations in inlet dust concentration profile. Flowfield calculations were performed on a Rolls Royce GEM-2 and splittered GEM-60 impeller, which both represent the high pressure stage of the axial + centrifugal compression system of GEM engines. A procedure developed by Tourlidakis, for the analysis of steady viscous flow in high speed centrifugal compressors with tip leakage, was used to generate the flowfields. The GEM-2 impeller flowfield was analysed at 1009c speed, and validated with calculations and measurements which had been taken for previous projects. Simulated erosion data under the same conditions was checked using practical results obtained in a Rolls Royce PLC Helicopter Engine Environmental Protection Programme, and good agreement was achieved. In order to provide a qualitative, experimental assessment of erosion, a GEM-60 impeller was coated with four layers of paint of different colours. Two sizes of quartz particle, each at three different vane heights, were then seeded into the impeller while it was run cold at (the maximum) 70% speed. The erosion patterns generated compared well with the results generated by the Particle Trajectory Code.Item Open Access High temperature particle -to-metal interaction in a simulated gas turbine environment(Cranfield University, 2002-05) Salama, I. M.; Elder, R. L.; Tan, S. C.An experimental study of the particle-to-metal interaction during high temperatures and velocity impact conditions is presented. A novel continuous erosion testing facility have been used to study the effect of particle and metal target temperatures as well as impact particle velocity on the erosion/deposition behaviour of the stainless steel 321, Nimonic 75, and aluminium target materials. The study was carried out to provide database information on the behaviour of those metals under simulated gas turbine conditions. The erosive particles used were quartz sand with diameters ranging from 20-30 μm. The erosion characteristics of stainless steel 321 were recorded at target surface temperature of 285°C, 415°C, 570°C and 715°C. The tests were carried out at two different impingement angles of 30° and 60° and at particle impact velocities of up to 300m/s. The effects of particle temperatures of 550°C, 750°C and 950°C on erosion/deposition rates were examined. The Nimonic 75 target temperatures were slightly modified to give a similar surface to melting point ratio as the stainless steel. The Nimonic 75 was tested at 545°C, 685°C, 825°C and 965°C surface temperatures and at the same particle velocities and temperature used for the stainless steel tests. The Nimonic targets were only tested at one impact angle of 30°. The aluminium targets were only tested at an impact angle of 60° and particle impact velocity of 100 m/s. The surface temperature was modified to give a ratio up to 0.8 of the melting point temperature, where the particle temperature was set to be 350°C, 550°C and 750°C. It was found that particle and target temperatures, impact velocity and angle have a significant effect on the erosion/deposition characteristics. There is a threshold target and particle temperature for which deposition begins, and it depends on impact velocity and angle. The Nimonic 75 targets exhibit a better resistance to particle deposition over the stainless steel 321 at high impact velocity and temperatures. Simple models of the erosion/deposition were established to describe the conditions of particle deposition on the stainless steel and Nimonic targets. The aluminium targets show an increase in the erosion rate as target temperature reaches certain level, which then drops as target temperature continues to increase beyond this point.Item Open Access A Study of Particle Trajectories In A Gas Turbine Intake(Cranfield University, 1988-01) Tan, S. C.; Elder, R. L.An experimental and theoretical study of the particle trajectories in a gas turbine intake has been presented. computer model was written to simulate a particle behaviour flight in a theoretical flow which was assumed to inviscid, irrotational and incompressible. The model is also on other assumptions which imposes several limitations the accuracy of the predicted results. These limitations the objectives of the experimental investigation of particle trajectories which was carried out in a 30.0 section of an axisymmetric helicopter inertial separator. The separator section was fully instrumented with pressure tappings to determine the near-wall flow condition. The flowfield at the central (vertical) plane of separator was also measured with a two spot laser anemometer. The dust particles used in the tests were the spherical ballotini and irregular quartz particles with diameter ranging f-rom 15.0 to 150.0 microns. These particles seeded locally into the separator at three initial positions. The restitution ratios for the quartz particle based on experimental data and the ballotini particle's were based on a simple relation, which was derived by and error matching of predicted and experimental results. The particle trajectories, velocities and angles in separator were measured at several stations using the anemometer. The measured results were compared with predicted values from the model which has been modified accept both the experimentally measured and inviscid flowfield. The particle shape factor was also included to account for the higher drag on the non-spherical particle. Further modification was also made to include the restitution ratios of the ballotini particle. Good agreement found between measured and predicted particle trajecto- velocities and angles for both the spherical and non- spherical particle. The trajectories of the large particles (>100. Oum) are ballistic' in nature which are governed by the inertia forces. The trajectories of the smaller particles are influenced by the both aerodynamic and inertia forces.Item Open Access A Study of Rocket Exhaust Particles(Cranfield University, 1996-10) Dennis, C. W.; Elder, R. L.; Lawrence, R. E.; Oxley, J. L.; Tan, S. C.The exhaust -plumes generated by rocket motors are of significant military importance for missile detection, recognition and communication due to their electromagnetic emission and propagation properties. The plume is a high temperature, high velocity stream of gas and particles, into which the surrounding air is entrained. With improvements in the modelling of plume gas chemistry and turbulence, particles present in the plume have become more important in the computational prediction of the plume's flow field, and the subsequent prediction of plume emission and propagation characteristics. This thesis describes research on plume particles, including the measurement of their physical characteristics and the addition of two phase coding (ie. particles) into current plume prediction software. Particle collections were carried out in plumes produced by rocket motors with double base and composite propellants (including aluminised). The collected particles were analysed to establish their chemical composition and size distribution. A laser Doppler anemometer system was successfully used to measure particle velocities in the plumes of 1.5kN double base motors. Particle tracking software was used to trace the paths of particles using a simplified prediction of the plume and it was found that the predicted particle behaviour was analogous to that measured experimentally. Project management software was used during the research and its relevance was assessed in respect to the project's size and nature. The management of experimental trials was studied and a methodology formulated to help improve their future operation. The costs and benefits of the research were assessed and compared to other research projects. Many of the benefits gained, such as measurement techniques, require marketing to ensure that they are exploited in the future. Recommendations for future research are given that should enhance the present work.Item Open Access Turbomachinery performance degradation due to erosion effect(Cranfield University, 2001-09) Ghenaiet, Adel; Elder, R. L.; Tan, S. C.Erosion of gas turbines operating in sandy or dusty environments can result in serious damage to the engine components, particularly the compressor unit. This phenomenon is a result of the ingestion of the sand particles into the engine and their consequent abrasive impacts on the blade surfaces. In order to understand the mechanism of sand ingestion and the resulting performance degradation, a general methodology has been developed for predicting the trajectories of particles, the erosion rates and blade profile changes, with predictive capabilities for performance degradations within more general configurations of turbomachines. This methodology was applied to an axial fan with upstream guide vanes (contra whirl) and was supported by experimental results. The numerical models for calculating the particle trajectory are based on the Lagrangian tracking technique and the eddy lifetime concept. The turbulence effect is assumed to prevail as long as the particle eddy interaction time is less than the eddy lifetime, and the displacement of a particle relative to the eddy is less than the eddy length. The flow field was solved separately using the Navier-Stokes finite volume flow solver " TASCflow " commercially available from ASC. The governing equations of the particle motion are solved using the Runge-Kutta Fehlberg technique. The tracking of particles and their locations is based on a finite element interpolation method. The developed Fortran code for predicting particle trajectory and erosion due to particle impact accounts for different types of boundary conditions and handles different frames of reference. The fragmentation of particles after rebound was also implemented. The number of particles seeded upstream of the IGV blades can be determined either by a user defined concentration profile or by a measured concentration profile. Also, particles can be seeded separately in a group at a release position. In the present study, the concentration profile and the initial particle velocity and angle of particle spread were determined from a laser transit anemometer. Two types of particles were used, a narrow size bandwidth (150-300micron) quartz particle and MIL-E5007E quartz particle, both of which have a normal distribution. The global rate of erosion, the reduced mass of blades and the changes of the blade geometry were predicted and compared with experimental results at different concentration levels. The baseline axial fan characteristics were measured at different mass flow conditions at a constant speed of rotation. To assess the effects of erosion, the characteristic measurement was repeated after each step of sand ingestion. The predicted aerodynamic performance; adiabatic efficiency, pressure rise coefficient and stall margin before and after erosion degradation were also determined from a developed Fortran program, which is basically a mean line method that uses advanced correlations for aerodynamic losses. Prediction of the particle trajectories show that high numbers of impacts (and maximum erosion) occurred near leading edge and tip region, which were also borne out by locally injected sand tests. The global rate of erosion and the consequent changes of the blade geometry were also predicted and compared with experimental results. The erosion pattern at high concentration of MIL-E5007E sand particles depicts net loss of material over the leading edge and the tip corner. The tip clearance increased markedly with a rounding of blade leading edge, which is the main cause of the decrease in efficiency, pressure rise, and surge margin. A parametric study with turbulence and fragmentation effects show that both parameters can influence the erosion rate and blade geometry deterioration. The results of the aerodynamic performance simulation using mean line method, which includes an erosion fault model, show good agreement with experimental results.