Browsing by Author "Goulas, A."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Open Access Flow inside axial pump impellers(Cranfield University, 1982-12) Resnick, Avi; Goulas, A.The subject of this work is the flow inside an axial pump impeller, which is studied both numerically and experimentally. The aim of the work is to provide a numerical method to predict the three-dimensional flow field within an axial flow pump impeller. The numerical scheme is divided into three basic parts. The first part involves the matrix through flow method to obtain the mainstream flow profiles on various blade-to-blade stream surfaces distributed from hub to tip and for given boundary conditions. In addition these solutions w to obtain a detailed flow field in the region of the leading edge. Furthermore, the transport equations of vorticity are integrated along each streamline to obtain the normal and stream wise components of vorticity.Item Open Access The prediction of transonic flows using a potential method(1986-09-26) Toolsie, K. O.; Goulas, A.; Elder, R. L.Transonic flows are simulated within convergent divergent nozzles and within turbomachinery blade rows. The flow is represented by the conservative full potential equation approximated by a nine-node central-difference scheme, which is third order accurate. Artificial viscosity is included into the central-difference approximation of the potential equation, in regions where the flow is locally supersonic. The approximation of the potential equation by central-differences, with an artificial viscosity term included, is equivalent to the approximation by upwind differences and ensures that the upwind nature of the domain of dependence of supersonic flows is correctly modelled. The exact form of this artificial viscosity term is derived and contains third order derivatives of velocity-potential. The inclusion of artificial-viscosity allows the potential equation to be approximated everywhere by central-differences and the flow equation is everywhere elliptic. The Neuman boundary-condition is applied, along solid surfaces, if an inviscid solution is desired. Viscous effects are incorporated by the modification of this condition so as to allow a transpiration flow through the solid surfaces. A standard Successive-Line-Over-Relaxation technique, developed for the solution of simultaneous elliptic equations, is used to solve the discretized potential flow equations. Predictions are presented for both the inviscid and the viscous-corrected potential codes applied to the simulation of transonic flow through nozzles and cascade blade-rows. Comparisons are made with other theoretical models and with experimental data. The problem of non-uniqueness is considered and an estimate of numerical error is made by the application of the inviscid code with two computational grids of different levels of refinement. The stability of this potential code is examined and is found to depend on the level of smearing of the shock discontinuity predicted by the theoretical model.Item Open Access A theoretical and experimental investigation of erosion prone areas on the blade surfaces of a centrifugal impeller handling granular solids.(1982-11) Ahmad, Khaled; Goulas, A.The erosion prone areas on the blade surfaces of a centrifugal impeller handling granular solids have been investigated both theoretically and eperimentally. The objective of the theoretical study is to develop software to predict the erosion prone areas on the blade surfaces of a slurry handling impeller. The basic concept in the theoretical study has been to find the particle trajectories inside the impeller. The governing equations of the motion of particles within the impeller are solved in a stepwise manner with time for a given flow field. The flow field is calculated by solving the conservation equations for the flow, using a finite difference method. The number density of the particles in the cross-section of the pipe through which the particles enter the impeller is calculated by applying a discretization procedure to the insitu concentration profile of the particles. The damage to the surface caused by impacting particles is estimated by calculating the velocity and the angle at which the particles impact on a surface. The material property of the particle or the surface does not explicitly enter into calculations. It is shown that for a given combination of particles and surface material, the material property of the particles and the surface can be isolated. In this way a relative measure of the depth of volume loss at different positions of the surface can be calculated. The surface can then be divided into a number of erosion prone areas. The model is tested by undertaking a number of experiments using a commercially available slurry pump which handled a mixture of fine pea gravels in water. The predicted erosion pattern suggested the area near the leading edge to be the most erosion prone zone. The agreement with the experimental results in this respect was satisfactory. The extent of the erosion zone on the blade surface as suggested by the analytical model was in close agreement with the experimental values. The analytical model also suggested that the major part of the erosion areas would lie near the back shroud of the impeller. This was in close agreement with the experimental results.