Hirokazu Kawabata

Experimental and Numerical Investigations of Effects of Flow Control Devices Upon Flat-Plate Film Cooling Performance

This study deals with the experimental and numerical studies of the effect of flow control devices (FCDs) on the film cooling performance of a circular cooling hole on a flat plate. Two types of FCDs with different heights are examined in this study, where each of them is mounted to the flat plate upstream of the cooling hole by changing its lateral position with respect to the hole centerline. In order to measure the film effectiveness as well as heat transfer downstream of the cooling hole with upstream FCD, a transient method using a high-resolution infrared camera is adopted. The velocity field downstream of the cooling hole is captured by 3D laser Doppler velocimeter (LDV). Furthermore, the aerodynamic loss associated with the cooling hole with/without FCD is measured by a total pressure probe rake. The experiments are carried out at blowing ratios ranging from 0.5 to 1.0. In addition, numerical simulations are also made to have a better understanding of the flow field. LES approach is employed to solve the flow field and visualize the vortex structure around the cooling hole with FCD. When a taller FCD is mounted to the plate, the film effectiveness tends to increase due to the vortex structure generated by the FCD. As FCD is laterally shifted from the centerline, the film effectiveness increases, while the lift-off of cooling air is also promoted when FCD is put on the center line.

Improvement of Flat-Plate Film Cooling Performance by Double Flow Control Devices: Part I — Investigations on Capability of a Base-Type Device

This paper deals with effects of double flow control devices (DFCDs) on flat plate film cooling performance. Aiming for further improvement of film effectiveness of discrete cooling holes, this new type of controlling method is invented and recently patented by the authors. The performance of base-type DFCDs, installed just upstream of cooling holes with conventional round or fan-shaped exits, is thoroughly investigated and reported in this study. Effects of the hole pitch are examined. Three hole-pitch cases, 3.0d, 4.5 d and 6.0 d are examined in this study to explore a possibility of reducing the cooling air by the application of DFCDs, where d is a hole diameter. In order to investigate the film effectiveness, a transient method using a high-resolution infrared camera is adopted. At the downstream of the cooling hole, the time-averaged temperature field is captured by a thermocouple rake and the time-averaged velocity field is captured by 3D Laser Doppler Velocimeter (LDV), respectively. Furthermore, the aerodynamic loss characteristics of the cooling hole with and without DFCDs are measured by a total pressure probe rake. The experiments are carried out for two blowing ratios, 0.5 and 1.0. It is found that DFCDs are quite effective in increasing the film effectiveness not only for round but also the fan-shaped holes.Starting from the base-type device, a robust optimization using Taguchi Method has been made by the present authors and will be reported as Part II.Copyright

Experimental and Numerical Studies on Leading Edge Film Cooling Performance: Effects of Hole Exit Shape and Freestream Turbulence

This study deals with the experimental and numerical studies of the effect of hole exit shape and free-stream turbulence on turbine blade leading edge film cooling. The study examines several test cases with two blowing ratios (BR = 1.0 and 2.0) and three mainstream turbulence intensities (1.0, 3.3 and 12.0%) using two types of leading edge models with cylindrical holes and diffuser holes [1]. The leading edge model consists of a semi-circular part of 80mm diameter and a flat after-body. In this study total pressure loss coefficient is measured by total pressure probe. Film effectiveness and heat transfer coefficient on the model surface are measured by the transient method using thermochromatic liquid crystal with video camera. In addition, detailed investigation of the film cooling is carried out using CFD simulations. RANS approach using Shear Stress Transport turbulence model and Detached Eddy Simulation (DES) approach are employed to solve the flow field. In the case of diffuser hole, the effect of mainstream turbulence intensity appears significant, and its spanwise averaged film effectiveness is decreased.Copyright

Improvement of Turbine Vane Film Cooling Performance by Double Flow-Control Devices

This study deals with the studies of the effect of flow control double device (DFCD) on a turbine vane film cooling. Aiming for improving film effectiveness, two semi-elliptical DFCDs per a pitch were attached obliquely upstream of the cooling hole. Since the DFCDs were applied to flat plate film cooling in the previous study, the applicability to the turbine vane was investigated in this study. In order to observe a flow field in detail, RANS CFD was conducted first. The DFCDs were installed upstream of each cooling hole of the pressure and suction sides of the vane to investigate the effect of the device position. In this paper, the effects of blowing ratio and cooling hole pitch were also investigated. The results obtained by CFD showed that the vortex generated from DFCD suppressed lift off of the secondary air. As a result, the film effectiveness became significantly higher than that without DFCD condition at high blowing ratio. Moreover, the improvement in the film effectiveness by DFCD was observed by both of the pressure and suction sides of the turbine vane. Based on the findings through RANS simulation, adiabatic effectiveness and total pressure loss coefficient measurement were performed in a linear cascade test facility. The experiment confirmed that the film effectiveness improved when DFCDs existed.

IMPROVEMENT OF FLAT-PLATE FILM COOLING PERFORMANCE BY DOUBLE FLOW CONTROL DEVICES: PART II - OPTIMIZATION OF DEVICE SHAPE AND ARRANGEMENT BY EXPERIMENT- AND CFD-BASED TAGUCHI METHOD

This paper, as a second part of the study on the double flow control device (DFCD) which has been proven in Part I [1] to improve the flat plate film cooling considerably, describes an approach to optimize the device shape and arrangement using Taguchi method. The target cooling holes are conventional cylindrical ones of 3.0d pitch with 35 deg angle to the flat plate surface. The shape of the double flow control device to be optimized is based on the hemi-spheroid used in Part I.The optimization process in this study is categorized as “static problem”, in which S/N ratios of “larger-the-better” characteristics are calculated for control parameters against their noise factor. The “larger-the-better” characteristics adopted in this study is the area averaged film effectiveness over the downstream region of the cooling hole. L18 orthogonal array is used to accommodate the experiment. Blowing ratios of the cooling air to the main flow used in this study are 0.5, 0.75 and 1.0, which are regarded as noise factor. Seven control parameters such as fillet radius, installation angle of the device are chosen and their effects on the film effectiveness are evaluated by the measurement as well as by RANS simulation. In this research, the optimization which used Taguchi method was at the same time carried out by an experiment and numerical simulation. From a comparison between the optimal parameter combinations attained from the measurement-based and CFD-based approaches, one can have an idea about the dependency of the optimal parameter combination on the characteristic evaluation approach. Additional investigation is also made on the effects of turbulence model upon the optimal parameter combination.The flow fields in the downstream region of the optimal DFCD are observed using 3D Laser Doppler Velocimeter in order to understand how the device works on the ejected cooling air. In addition, Large-Eddy-Simulation (LES) is also executed in order to grasp unsteady flow structures created by the device and their interaction with the cooling air. It is found from the measurement as well as the LES analysis that the optimal DFCD generates comparatively large-scale longitudinal vortices, causing the drastic increase in film effectiveness.Copyright

Improvement of Turbine Vane Film Cooling Performance by Double Flow Control Devices

This study deals with the studies of the effect of flow control double devices (DFCDs) on turbine vane film cooling. Aiming for improving film effectiveness, two semi-spheroid DFCDs per pitch were attached to the vane surface upstream of the cooling hole. Although the DFCDs were successfully applied to the flat plate film cooling in the previous study, the applicability to the turbine vane was to be investigated. In order to observe the flow field in detail, RANS simulation was conducted first. The DFCDs were installed upstream of each cooling hole of the pressure and suction sides of the vane to investigate the effect of the device position. In this paper, the effects of blowing ratio and cooling hole pitch were also investigated. The results obtained by CFD showed that the vortex generated from DFCD suppressed lift off of the secondary air. As a result, the film effectiveness became significantly higher than that without DFCD condition. Moreover, the improvement in the film effectiveness by DFCD was observed by both of the pressure and suction sides of the turbine vane. Based on the findings through RANS simulation, adiabatic effectiveness and total pressure loss coefficient measurement were performed in a linear cascade test facility. The experiment confirmed that the film effectiveness was improved when DFCDs existed.Copyright