No abstract

A method for centrifugal compressor impeller's multi-objective design optimization was developed. The method was applied to a tested twelve radial bladed centrifugal compressor impeller, available in the open literature, as a test case characterized by three-dimensional viscous turbulent flow structure. The optimization target was to maximize the total-to-total adiabatic efficiency, and pressure ratio of the impeller at the design point, considering constant mass flow rate, rotational speed, and nearly constant torque. The aerodynamic analysis was performed using (CFX BladeGen) commercial software. This software solves the three-dimensional turbulent Navier-Stokes flow equations, with zero-equation turbulence model using finite volume method. The capabilities of the software were first validated by comparing the computed results with, an experimental data made by Mizuki [10, 11]. In this experimental work, yaw probes distributed along the impeller channel, were used to determine total and static pressures for hub and shroud. GAlib software was used to apply Genetic algorithm for handling of the optimization problem. The optimal impeller configuration, which corresponds to maximum efficiency, and maximum pressure ratio, keeping the same mass flow rate and rpm, was obtained with only 0.7% violation of the original torque value. A comparison between original and optimized impellers was made, which revealed the causes for efficiency and pressure ratio improvements.

Theoretical and experimental investigations have been made to predict the performance of a backward-curved blade centrifugal pump. A mathematical model based on steady twodimensional incompressible Navier-Stokes (N-S) equations has been developed. The numerical solution was made using the primitive variables with artificial compressibility. The predictorcorrector method proposed by MacCormack was employed. The use of this technique involved imaginary rows behind walls, and periodic boundaries at far upstream and downstream which adequately improved the convergence to the solution. Based on this model a computer code has been developed and used to predict the flow pattern inside the pump and to determine the pump characteristics. A test rig was used to measure the real pump characteristic at controlled flow rates. Comparison of calculated and measured pump characteristic showed good agreement. Examination of the flow pattern at different flow rates might be useful to interpret the many performance features of the pump.

A theoretical investigation has been made to predict the flow pattern within a radial blade centrifugal pump. A mathematical model based on steady two-dimensional incompressible Navier-Stokes (N-S) equations has been developed. The real flow was modeled under these considerations. A computational-fluid-dynamic scheme was suggested using the primitive variables with artificial compressibility. The predictor-corrector method proposed by MacCormack was employed for its advantages of accuracy, less complexity, reasonable storage and convenient stability limit. A stability criterion was suggested and a fourth-order extrapolation smoothing term was used to limit the higher variations of the primitive variables. The use of this technique involved imaginary rows behind walls, and periodic boundaries at far upstream and downstream which adequately improved the convergence to the solution. Based on this model a computer program capable of predicting the flow pattern and pump characteristics inside the radial blade pump has been developed. The validity of the developed computer program, has been proven by comparing calculated and measured pump characteristic, which showed good agreement.

A nonlinear finite element model is provided for the thermal post buckling and linear flutter behavior of composite panels. Panel subjects to combined aerodynamic and thermal loads. The governing equations are derived using the classical plate theory and the principle of virtual work. The effect of large deflection is included in the formulation through the von Kármán nonlinear strain-displacement relations. To account for the temperature dependence on material properties, the thermal strain is stated as an integral quantity of the thermal expansion coefficient with respect to temperature. The aerodynamic pressure is modeled using the quasi-steady first order piston theory. The Newton-Raphson iteration method is employed to obtain the nonlinear aero-thermal post-buckling deflections, and a frequency-domain solution is presented to predict the critical dynamic pressure at different elevated temperatures. Finally, numerical results are provided to depict the optimum lamination scheme in order to maximize the aero-thermal stability of such panels. The optimum solution is obtained by Genetic Algorithms.