Takayuki Matsunuma

Characteristics of an Annular Turbine Cascade at Low Reynolds Numbers

The aerodynamic characteristics of turbine cascades are thought to be relatively satisfactory due to the favorable pressure gradient of the accelerating flow. But within the low Reynolds number region of approximately 6×104 where the 300kW ceramic gas turbines which are being developed under the New Sunshine Project of Japan operate, the characteristics such as boundary layer separation, reattachment and secondary flow which lead to prominent power losses can not be easily predicted.In this research, experiments have been conducted to evaluate the performance of an annular turbine stator cascade. Wakes of the cascade were measured using a single hot wire and five hole pressure tube, for a range of blade chord Reynolds numbers based on the inlet condition from 2×104 to 12×104. Flow visualizations on the suction surface of the blade were carried out using oil film method. At low Reynolds numbers, the flow structure in the annular cascade was quite complex and three-dimensional. The separation line on the suction surface moved upstream due to the decrease of Reynolds number. In addition, the growth of secondary flows, i.e., passage vortices and leakage vortex, was extremely under the influence of Reynolds number.Copyright

Influence of Turbulence Intensity on Annular Turbine Stator Aerodynamics at Low Reynolds Numbers

The aerodynamic characteristics of turbine cascades are thought to be relatively satisfactory due to the favorable pressure of the accelerating flow. But within the low Reynolds number region of 6×104 where the 300kW ceramic gas turbines which are being developed under the New Sunshine project of Japan operate, the characteristics such as boundary layer separation, reattachment and secondary flow which lead to prominent power losses can not be easily predicted.In this research, experiments have been conducted to evaluate the performance of an annular turbine stator cascade, especially focused on the influence of inlet turbulence intensity at low Reynolds numbers. The Reynolds number, based on inlet condition, was varied from 2×104 to 12×104. The turbulence intensity was changed between 0.5% and 8.9% by setting turbulence generation sheets. The wake of the cascade was measured using a 5-hole pressure probe and a single element hot-wire anemometry.The Reynolds number was a determinative important parameter, while the turbulence intensity was found to have an insignificant effect on the overall total pressure loss of annular turbine stator at low Reynolds numbers. However, the increase in separation zone on suction surface and the decrease of passage vortices near the endwalls were observed locally with the increase in the inlet turbulence intensity. Instantaneous velocity signals proved the transformation of the flow structure in separation zone. The increase in profile loss (separation) and the decrease in net secondary loss (passage vonices) offset each other. Therefore, the net overall loss remains almost constant.© 1999 ASME

LDV Measurements of Unsteady Flow in a Turbine Rotor

V2 time-averaged and mass-averaged relative velocity at rotor exit plane (plane 44, axial distance ZRT / Cax,RT = 1.459) The unsteady flow field in an axial-flow turbine rotor under low Reynolds number condition (Reout,RT = 3.60×10) was investigated experimentally using a laser Doppler velocimetry (LDV) system. Detailed measurements of the time-dependent unsteady distributions of velocity, flow angle, turbulence intensity and Reynolds stress were carried out at design operating condition. The obtained data was analyzed in terms of both absolute (stationary) frame of reference and relative (rotating) frame of reference. The effect of stator wake and secondary vortices on the flow field inside the rotor passage was clearly determined. X pitch-wise distance ZRT axial distance from rotor leading edge ZST axial distance from stator leading edge θ flow angle measured from axial direction vx’vz’ velocity correlation (Reynolds stress) Subscripts Abs absolute flow or absolute frame of reference in stator or rotor inlet value out stator or rotor outlet value Rel relative flow or relative frame of reference RT rotor value ST stator value Nomenclature Introduction Cax axial chord length With the new generation of small-sized gas turbine engines, low Reynolds number flows have become increasingly important. Blade Reynolds numbers for the turbine stage of small-sized gas turbines can drop below 10. At these low Reynolds number conditions, the boundary layer is dominated by laminar flow and is susceptible to flow separation, which is associated with increased loss and reduced performance. Recently, a lot of studies focused on the characteristics of turbine Re Reynolds number t time TRT rotor passing period in absolute frame TST stator passing period in relative frame Tu turbulence intensity V velocity V1 time-averaged and mass-averaged absolute velocity at stator exit plane (plane 1, axial distance ZST / Cax,ST = 1.075) 1 American Institute of Aeronaut 32nd AIAA Fluid Dynamics Conference and Exhibit 24-26 June 2002, St. Louis, Missouri AIAA 2002-2742 Copyright

Research and Development of Practical Industrial Cogeneration Technology in Japan

This paper presents an overview of a development project involving industrial cogeneration technology using 8,000-kW class hybrid gas turbines in which both metal and ceramics are used in parts subject to high temperatures in order to achieve high efficiency and low pollution.The development of hybrid gas turbines focuses mainly on the earlier commercialization of the turbine system. Stationary parts such as combustor liners, transition ducts, and first-stage turbine nozzles (stationary blades) are expected to be fabricated from ceramics. The project aims at developing material for these ceramic parts that will have a superior resistance to heat and oxidation. The project also aims at designing and prototyping a hybrid gas turbine system to analyze the operation in order to improve the performance. Furthermore, the prototyped hybrid gas turbine system will be tested for long-term operation (4,000 hours) to verify that the system can withstand commercialization. Studies will be conducted to ensure that the system’s soundness and reliability are sufficient for industrial cogeneration applications.Copyright

Applications of String-type DBD Plasma Actuators for Flow Control in Turbomachineries

String-type dielectric barrier discharge plasma actuators (string-type DBD-PAs) , which consist of metallic wires coated by insulating materials and exposed electrodes, were developed for enlarging the usages in various turbomachineries, such as technologies for mitigating flow separation and tip leakage flow. Properties of flow induced by various stirng-type DBD-PAs were analyzed by PIV measurements. New tube-type DBD-PA made of quartz glass tube was also manufactured and feasibility tests showed that it can have greater durability by injecting gases for cooling and by being used under higher temperatures found in realistic conditions where the turbomachineries such as gas turbines are working.