Ichiro Ariga

Stabilizing and Destabilizing Effects of Coriolis Force on Two-Dimensional Laminar and Turbulent Boundary Layers

To investigate the effects of Coriolis force on two-dimensional laminar and turbulent boundary layers, quantitative experiments were performed. A numerical evaluation was also carried out utilizing the Monin-Oboukhov coefficient including the effect of rotation. From the experimental results, the boundary layer development was found to be promoted on the unstable side and suppressed on the stable side, in comparison with the case of zero-rotation. In the stable boundary layer, the critical Reynolds number for relaminarization was observed to increase as rotation number was decreased. Calculated results were seen to predict the stabilizing effect of Coriolis force fairly well.

Effects of Fluid Leakage on Performance of a Centrifugal Compressor

Fluid loss caused by leaks through the impeller tip clearance was investigated for a centrifugal compressor. Operating conditions, Reynolds number, and clearance were varied independently during the experiment. It was found that the average compressor performance would be reduced by about 4 percent when the relative clearance was increased from 0.0125 to 0.125 and the resulting leakage loss was dependent on the Reynolds number, the tendency of which was just opposite in case of wall friction loss, as was well-known. Moreover, a determination of the leakage loss coefficient was made as a function of the relative clearance, relative leak level and the Reynolds number as the result of this experiment.

Investigation Concerning the Blade Loading of Centrifugal Impellers

An investigation concerning the optimum blade loading of centrifugal impellers was performed. The three impellers with straight radial blades employed in the present study were of the same configurations except the shroud profiles which rendered to bring different diffusion ratios from each other. The static pressure distributions on blade surfaces, flow patterns within the impeller channel as well as at impeller inlet and at outlet were measured for these impellers. The effect of a secondary flow within impeller channel was clarified to some extent from the measurements. Theoretical investigation was also performed in order to compare with the experimental data.Copyright

Effects of Reynolds Number on Performance Characteristics of a Centrifugal Compressor

The influences of the Reynolds number on centrifugal compressor performance have not so much been investigated. Especially, the experimental equation representing the rates of losses for the critical Reynolds number has been seemingly not established. Namely, the coefficients in the equation differ with each investigator. In the present study, an experiment was conducted by means of an experimental centrifugal compressor. From the results, it was found that the critical Reynolds number Recmeancr was reasonable for the compressor stage as well as for the impeller, and for the former it amounted to about 0.9∼1.3 × 105, while for the latter it amounted to about 0.9∼1.2 × 105. On the other hand, the critical Reynolds number Rec2cr was also found appropriate for the diffuser and it amounted to about 0.9∼1.5 × 105. In addition, the coefficients in the experimental equation which introduced the rate of losses were estimated.Copyright

On the Performance Prediction of a Centrifugal Compressor Scaled Up

A centrifugal compressor performance prediction method, in which each loss generated within the compressor stage was estimated by recognizing the individual relationship with Mach number, was investigated over a wide range of sizes and types. Calculation formulae for the losses were established by analyzing test results. It was confirmed that the formulae could be applied to predict the performance levels of compressors with impeller diameters from 78 mm to 640 mm by refering to unpublished test data obtained experimentally by other researchers. From the results, it could be deduced that: (1) The wall friction losses and the secondary flow losses within the compressor decreased with increase of impeller size. (2) The leakage flow losses were found to increase when scaling up the compressor, even when tip clearance/blade height were held constant. The present paper presents a progress report of work still underway.Copyright

Reversed Flow Phenomena Within Centrifugal Compressor Channels at Lower Flow Rate

It is recognized today that centrifugal compressors exhibit their inherent characteristics at lower flow rate and this is due to the reversed flow phenomena taking place within compressor channels. In the present study, the authors precisely observed these reversed flow phenomena within compressor channels in an experiment. Many sorts of measuring techniques were employed to clarify the nature of them. By these investigations, it became clear that these phenomena primarily depended on the shocked inlet condition at inducer inlet, where shocked inlet condition designated that the direction of the relative velocity at the inducer inlet deviated from the inducer mean camber line there. Especially, the balance of the body forces and the pressure gradients between the separated wake flow and the main flow was a predominant factor. Reversed flow phenomena observed within compressor channels appeared within the inlet duct near the shroud casing, within the inducer and impeller channel as a three-dimensionally skewed eddy, at the walls of the diffuser, and along the shroud casing.Copyright

A Study on the Flow Mechanism Within Centrifugal Impeller Channels

Investigations concerning the flow patterns within centrifugal impeller channels have been made for many years. However, many of the problems remain unresolved about the secondary flow and the loss production mechanism within impeller channels. In the present study, measurements of the flow mechanism within impeller channels under the off-design conditions were performed by employing yaw probes to compare the results with those at the design point. The impellers with straight radial blades employed in the present study were of the same configuration except the shroud profiles which made diffusion ratios different from each other. From the present results, it became clear that the loss production mechanisms and the flow patterns within impeller channels were essentially unvaried both under design and off-design operations. The results thus obtained by the present study were furthermore compared with the others to examine the reliability of these results.Copyright

Investigations Concerning Flow Patterns Within the Impeller Channels of Radial-Inflow Turbines, With Some Reference to the Influence of the Splitter Vanes

The experimental results of the relative velocity distributions together with the static pressure distributions within the impeller channels of radial-inflow turbines with and without splitter vanes are presented. The flow patterns within three stream surfaces (blade-to-blade surfaces) having different passage depths are shown using two performance parameters, i.e., nondimensional weight flow and nondimensional rotation speed. The impellers used were of purely radial type or of two-dimensional type. Further, theoretical predictions for the relative velocity distributions within the impeller channels having no splitter vanes were conducted, and comparisons of the theoretical results with experimental data were made.

Advances in Unsteady Turbomachinery Aerodynamics in Japan: Professor Gallus’ Contribution

The present paper describes recent advances in turbomachinery aerodynamic research in Japan achieved by the researchers who studied under the supervision of the late Professor Gallus. His research work, way of thinking, and personality exerted great influence in Japan on the styles of research in the field of unsteady aerodynamics of turbomachines. The profound contribution by him to the research and development of Japanese gas turbine technologies is highly appreciated. The paper presents research results on the issues concerning cascade flutter suppression, rotating stall analysis and control for axial compressors, unsteady flow analysis and control for radial compressors and diffusers, as well as design studies of axial turbomachines.Copyright