Shimpei Mizuki

Control of Surge for Centrifugal Compression System by Using a Bouncing Ball

An experimental study for the control of surge in a centrifugal compression system by using a bouncing ball was tried. The bouncing ball was placed on a hole outside of the upper wall of a plenum installed to a delivery of a compressor. The hole was surrounded by a tube and had the conical slope toward the hole. When surge occurred, the ball bounced by the fluctuating pressure force in an irregular manner.By the irregular fluctuation of the bouncing ball, the frequency of surge was suppressed. The peak in the spectrum caused by surge disappeared. Thus, the simple method to control surge by using the bouncing ball was shown to be effective.Copyright

Unsteady Flow Within Centrifugal Compressor Channels Under Rotating Stall and Surge

Unsteady flow patterns throughout a centrifugal compressor system during the rotating stall and the surge were measured experimentally. Various kinds of unsteady behaviors of the flow appeared both continuously and suddenly as the flow rate decreased. The part-span stall, the full-span stall, the mild and the deep stalls and the deep surge appeared clearly. The fluctuations caused by the full-span stall were seen even during the surge and affected the flow within the scroll through the vaneless diffuser. The experimental results were compared with those computed by the lumped parameter theory. The good agreements between them were obtained when the appropriate values were selected for the lumped parameters.Copyright

Numerical Investigation of Effects of Incidence Angle on Aerodynamic Performance of Ultra-Highly Loaded Turbine Cascade

An increase in turbine blade loading is a useful means to improve the performance characteristics of gas turbines. This paper describes the results of numerical investigation for the internal flow within a low speed linear ultra highly loaded turbine cascade (UHLTC) at the off design condition. The present UHLTC has the design inlet flow, angle of 80 degree and the blade turning angle of 160 degree. The computations were made for the incidence angles from −30.0 to +7.5 degree relative to the design incidence. The two dimensional computations were carried out for eight incidence angles in order to reveal the effects of incidence on the profile loss of UHLTC. Subsequently, the three dimensional computations were performed for the several incidence angles to clarify the sensitivity of secondary flow and the associated loss generation mechanisms to the change of incidence angle. The influences of incidence variation on the blade loading were also examined. The computed results showed that the loss generation and the strength and the structure of secondary flows were much sensitive to the increase of incidence angle from the design incidence. On the other hand, the decrease of the incidence from the design one did not give the strong effect for the loss generation and the blade loading.Copyright

Analysis of Flow Within Pump Impeller of Torque Converter

It is difficult to measure flow patterns within rotating elements of a torque converter due to the complicated construction. Therefore, the numerical calculation is considered to be an effective tool to know the internal flow. Three-dimensional incompressible turbulent flow within a pump impeller of an automotive torque converter was analyzed numerically at three different speed ratios, 0.02, 0.4 and 0.8 under the same inlet boundary condition. The speed ratio was defined as the ratio of rotating speed of the turbine impeller to that of the pump. The governing equations using the k-e model in the physical component tensor form were solved with a boundary-fitted coordinate system fixed on a rotating impeller. The solution algorithm was the SIMPLE method applied to the curvilinear coordinate system. The computed results were compared with those obtained experimentally by an oil film flow visualization technique for the pressure, suction, core and shell surfaces. Moreover, the results at three different speed ratios were examined in detail in order to clarify the behavior of secondary flow patterns. The computed results showed good agreement with the experimental results and clarified the behavior of the complicated flow patterns. The secondary flow patterns were strongly influenced by the correlation between the intensities of the Corinlis force (COF) and the centrifugal force due to the passage curvature in the meridional plane (CMF).© 1996 ASME

A Simulation of Secondary Flow in Centrifugal Impeller Channel by a Stationary Three-Dimensional Curved Duct

A duct with three-dimensional curvatures was employed in order to investigate the complex secondary flow patterns similar to those within centrifugal impellers. The curvature within a pair of co-cylindrical surfaces of the duct simulates that within the meridional plane of an impeller, and the curvature within the other pair of co-cylindrical surfaces perpendicular to the above-mentioned surfaces simulates the effect of the Coriolis force within the blade-to-blade surface. The computed and the measured results showed the qualitative similarity of the secondary flow patterns to those within centrifugal impellers except the effects of pressure rise by the centrifugal force generated by the impeller rotation and the tip leakage flow.Copyright

Investigation for Secondary Flow and Loss Generation Mechanisms within Centrifugal Impeller by Using Rotating Curved Duct (1st Report, Influence of Rossby Number)

The objective of this study is to reveal the effects of the passage vortex on the loss generation within a centrifugal impeller by numerically analyzing the flow within the rotating curved duct which is considered to be a simplified model for centrifugal impeller channels. In a centrifugal impeller, the behavior of passage vortex is strongly influenced by the centrifugal force caused by the curvature of the impeller passage and the Coriolis force induced by the rotation. Therefore, the Rossby number, which is defined as the ratio of the former force to the latter, is chosen as the major parameter in the present study. The computed results revealed that the location of the high loss region at the exit of the bend strongly depended on the Rossby number. Moreover, the strength of the secondary flow and the associated losses were remarkably increased by the decrease of the Rossby number less than 1.0.

Investigation for Loss Generation Mechanisms of Flow in Turbomachinery by Usin Curved Square Duct (3rd Report, Influence of Curved Angle)

In a series of present studies, the flows within the stationary curved ducts are analyzed numerically with the aerodynamic or the geometrical parameters affecting the loss generation caused by the passage vortex within a passage of a turbomachinery. In the former reports, the inlet boundary layer thickness and the inlet velocity distortion were taken as the aerodynamic parameter and the aspect ratio of the cross section was chosen as the geometrical parameter. In this report, the effects of the curved angle of the bend on the loss generation caused by the passage vortex are examined by relating the bend of curved duct to the blade to blade surface of an axial flow turbine cascade. The curved angle is changed from 90 to 160 degree by 10 degree with fixing the length of arc for the mean radius of curvature of the bend or fixing the mean radius of curvature.

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

Analysis of the Flow in Vaneless Diffusers With Large Width-to-Radius Ratios

The flow in vaneless diffusers with large width-to-radius ratios is analyzed by using three-dimensional boundary-layer theory. The variations of the wall shear angle in the layer and the separation radius of the turbulent boundary layer versus various parameters are calculated and compared with experimental data. The effect of the separation point on the performance of vaneless diffusers and the mechanism of rotating stall are discussed. It is concluded that when the flow rate becomes very low, the reverse flow zone on the diffuser walls extends toward the entry region of diffusers. When the rotating jet-wake flow with varying total pressure passes through the reverse flow region near the impeller outlet, rotating stall is generated. The influences of the radius ratio on the reverse flow occurrence as well as on the overall performance are also discussed.Copyright

NUMERICAL CALCULATION OF FLOW FOR CASCADE WITH TIP CLEARANCE

Three-dimensional incompressible turbulent flow within a linear turbine cascade with tip clearance is analyzed numerically. The governing equations involving the standard k — model are solved in the physical component tensor form with a boundary-fitted coordinate system. In the analysis, the blade tip geometry is treated accurately in order to predict the flow through the tip clearance in detail when the blades have large thicknesses. Although the number of grids employed in the present study is not enough because of the limitation of computer storage memory, the computed results show good agreements with the experimental results. Moreover, the results clearly exhibit the locus of minimum pressure on the rear part of the pressure surface at the blade tip. NOMENCLATURE A : total flux coefficient • : axial blade chord C, : static pressure coefficient • : total pressure coefficient g : determinant of metric tensor : contravariant component of metric tensor gu : covariant component of metric tensor H : span k : turbulent energy p : static pressure • : total pressure Re : Reynolds number