Hoshio Tsujita

Control of Surge in Centrifugal Compressor by Using a Nozzle Injection System: Universality in Optimal Position of Injection Nozzle

The passive control method for surge and rotating stall in centrifugal compressors by using a nozzle injection system was proposed to extend the stable operating range to the low flow rate. A part of the flow at the scroll outlet of a compressor was recirculated to an injection nozzle installed on the inner wall of the suction pipe of the compressor through the bypass pipe and injected to the impeller inlet. Two types of compressors were tested at the rotational speeds of 50,000 rpm and 60,000 rpm with the parameter of the circumferential position of the injection nozzle. The present experimental results revealed that the optimum circumferential position, which most effectively reduced the flow rate for the surge inception, existed at the opposite side of the tongue of the scroll against the rotational axis and did not depend on the compressor system and the rotational speeds.

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

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

Mechanism of Blockage Generation in Transonic Centrifugal Compressor at Design and Off-Design Conditions

In a transonic centrifugal compressor, the loss generation is intensified by the formation of the shock wave and consequently the blockage is expected to increase. The blockage is considered to influence not only the flow rate and the increase of the static pressure but also the stall inception. However, the detailed mechanism of the blockage generation in the transonic centrifugal compressor has not been fully clarified.In this study, in order to clarify the mechanisms of loss and blockage generations in the transonic centrifugal compressor which are expected to be strongly influenced by the operating condition, the flows in the compressor at the off-design condition as well as at the design condition were analyzed numerically. The verifications of the computed results were carried out by comparing with available experimental results. The computed result clarified that the loss generation near the impeller inlet at design condition was mainly caused by the interactions of the shock wave with the tip leakage vortex appearing from the leading edge of the main blade as well as the boundary layer on the suction surface of the main blade. Moreover, these interactions were intensified by the decrease of the flow rate, and consequently enhanced the blockage effects by the tip leakage vortex from the leading edge of the main blade and resulted in the increase of the aerodynamic loss especially along the shroud surface in the impeller passage. On the other hand, the decrease of the blockage effects by the tip leakage vortex from the main blade with the increase of the flow rate formed the shock wave on the suction surface of the splitter blade at near-choke condition. This shock wave interacted with the tip leakage vortex from the splitter blade and consequently increased the aerodynamic loss.Copyright

Complex Secondary Flow and Associated Loss Generation in Ultra-Highly Loaded Turbine Cascade

An increase of turbine blade loading decreases the numbers of blades and stages, and results in the improvement of the performance characteristics of gas turbines. However, in such highly loaded turbine cascade with high turning angle, the secondary flow becomes much strong due to the steep pressure gradient across the blade-to-blade passage and deteriorates the performance of turbine enormously. In this study, the computations were performed for the flow in the ultra-highly loaded turbine cascade in order to clarify the effects of the inlet boundary layer thickness and the incidence angle which strongly influence the secondary flow structure in a turbine cascade. Moreover, the experimental oil flow visualization was conducted on the blade surface and the endwall, and the measurements of blade surface static pressure were performed at the midspan. The computed results agreed well with the oil flow visualization and the measured blade surface static pressure. The effects of the incidence angle and the inlet boundary layer thickness on the secondary flow structure, the total pressure loss, the secondary flow kinetic energy and the blade loading distributions were examined in detail. The positive incidence angle induced the characteristic vortex released from the endwall. Moreover, it was revealed that the interactions among the horseshoe vortex, the passage vortex and the characteristic vortex strongly increase the secondary loss in the cascade passage.Copyright

Numerical Analysis of Flow in Radial Turbine:(Effects of Nozzle Vane Angle on Internal Flow)

Variable Geometry System (VGS) is widely applied to the nozzle vane for the radial inflow turbine constituting automotive turbochargers for the purpose of optimizing the power output at each operating condition. In order to improve the performance of radial turbines with VGS, it is necessary to clarify the influences of the setting angle of nozzle vane on the internal flow of radial turbine. However, the experimental measurements are considered to be difficult for the flow in radial turbines because of the small size and the high rotational speed. In the present study, the numerical calculations were carried out for the flow in the radial turbine at three operating conditions by applying the corresponding nozzle vane exit angles, which were set up in the experimental study, as the inlet boundary condition. The numerical results revealed the characteristic flow behaviors at each operating condition.

20604 Numerical Analysis of Flow in Ultra Micro Centrifugal Compressor : Influence of Impeller Outlet Blade Angle

For an ultra micro centrifugal compressor, the applicability of two-dimensional (2D) blade has been investigated with the consideration of productivity in the downsizing of impeller. On the other hand, the improvement of the pressure recovery ratio in the diffuser is also required to increase the overall pressure ratio of a centrifugal compressor system. In this study, the flows in three types of centrifugal compressor impeller with the 2D blade which are different in the impeller outlet blade angle were analyzed numerically because the outlet blade angle is the most important design parameter to specify the shape of such impeller. The computed results clarified that the increase of impeller outlet blade angle reduces the tip leakage flow and the reversed flow at the impeller outlet, but increases the wall friction loss due to the increase of the cascade passage length.

20605 Investigation of Flow in Ultra-Highly Loaded Linear Turbine Cascade : Effects of Incidence Angle and Tip-Clearance

An increase of turbine blade loading by the increase of turning angle makes it possible to reduce the numbers of the blades and the stages, and consequently to decrease the size and the weight of gas turbine. However, the aerodynamic performance of turbine cascade may be decreased significantly by the strengthened secondary flow. In this study, the oil-flow visualization, the blade surface static pressure measurements and the detailed internal flow measurements by using the 5-hole Pitot tube were performed for the ultra-highly loaded turbine cascade with turning angle of 160 degree in order to clarify the effects of incidence angle and the existence of tip-clearance on the flow in the cascade. The present experimental results showed that the increase of incidence angle strengths the horseshoe vortex and passage vortex, and expands the high loss region at the downstream of turbine cascade, but does not so influence the formation of leakage vortex.