Hamid Hazby

Effects of Blade Deformation on the Performance of a High Flow Coefficient Mixed Flow Impeller

The effects of blade deformation under running conditions on the performance of a highly loaded transonic mixed flow impeller were investigated. Two impellers were manufactured, one using the “running” blade profiles as designed and one using the converted “unrunning” or “cold” geometry. Both impellers were tested experimentally and investigated numerically. The test data taken with smooth casing showed that at maximum speed, the isentropic efficiency and pressure ratio of the running geometry was higher than the unrunning geometry by about 0.4% and 1.4%, respectively. However, the difference in performance diminished in the presence of recirculating casing treatment. Numerical calculations suggested that the differences at high speeds were mainly due to the variation in the impeller tip clearance. The calculations using deformed blade profiles under centrifugal load only, predicted performance differences which were about twice as high as the measured values. However, closer predictions were obtained when the effects of pressure loads on blade deformation were included using closely coupled fluid-structural analyses.

The Design of a Family of Process Compressor Stages

The design of a new family of process compressor stages is described. The paper discusses the choice of master and derived stages to cover the required flow range and provides guidelines for the design of the stage components, including the impeller, diffuser and the return channel. Details are given of the mechanical and aerodynamic design process and the computational tools used for this. The test results show that the performance objectives have been achieved. Results from testing of some of the stages are compared with CFD simulations. These show that the inclusion of real geometry features, such as the shroud and hub leakage paths and the end-wall fillets, is necessary to obtain good agreement with the measured performance.

Role of Tip Leakage in Stall of a Transonic Centrifugal Impeller

The objective of the current paper is to employ numerical simulations to identify flow features, which could lead to the breakdown of stable operation in transonic centrifugal impellers at near-stall operating conditions. Steady state three-dimensional viscous flow calculations are used to investigate the flow inside a transonic impeller representative of state of the art automotive turbocharger technology. The detailed impeller flow field is compared at different operating conditions. It is observed that the interaction of the relative total pressure deficit coming from the main blade tip region and the adverse pressure gradient in the splitter passage results in a breakdown of the flow in the tip region. These low relative total pressure fluids originate from the main blade tip leakage flow and/or the transported boundary layers. Effects due to the splitter wall shear stress and the turbulence model on the flow are also investigated and addressed in the paper.© 2009 ASME

Investigation of the flow in a small-scale turbocharger centrifugal compressor

This paper presents an experimental and numerical study of the flow in a 1:1 scale, automotive turbocharger centrifugal compressor. Particle image velocimetry measurements have been carried out in the vaneless diffuser at 50% of the design speed. The challenges involved in taking optical measurements in the current small-scale compressor rig are discussed. The overall stage performance and the measured diffuser flow are compared with the results of steady-state computational fluid dynamics calculations. A good agreement between the computational fluid dynamics and the experimental results demonstrates that the numerical methods are capable of predicting the main flow features within the compressor. The synthesis of measured and predicted data is used to explain the sources of the flow and performance variations across the compressor map, and the differences in loss production between small and large compressors are highlighted.

Effect of a Recirculation Device on the Performance of Transonic Mixed Flow Compressors

Two transonic mixed flow compressors with an extremely high flow coefficient of ϕ = 0.25 and pressure ratios of 2.5 and 2.65 have been designed and tested. CFD simulations indicated that both impellers operate with a suction surface relative Mach number of above 1.5 at their design conditions. Both compressors achieved a narrow stable operating range when tested without recirculation devices.The effects of two different recirculation devices on the compressor performance maps were investigated both experimentally and numerically. The first type is a widely used recirculation device which consists of an upstream slot, bleed slot and an annular cavity which connects both slots. The other has vanes installed in the cavity which were designed to provide a recirculation flow with negative swirl at the impeller inlet. Measurement data demonstrated the effect of the recirculation devices on increasing the range of these two transonic mixed flow compressors and showed the superiority of the recirculation device with vanes.The effects of the recirculation devices on the impeller flow field at near surge conditions are studied using steady state 3D CFD calculations. Both measurements and simulations showed that the stability enhancement is partly caused by a steeper pressure rise characteristic.© 2014 ASME