Masaya Kumada

Tip Clearance Effect on Heat Transfer and Leakage Flows on the Shroud-Wall Surface in an Axial Flow Turbine

An axial flow turbine for a turbocharger is used as a test turbine, and the local heat transfer coefficient on the surface of the shroud is measured under uniform heat flux conditions. The nature of the tip clearance flow on the shroud surface and a flow pattern in the downstream region of the rotor blades are studied, and measurements are obtained by using a hot-wire anemometer in combination with a periodic multisampling and an ensemble averaging technique. Data are obtained under on- and off-design conditions. The effects of inlet flow angle, rotational speed and tip clearance on the local heat transfer coefficient are elucidated. The mean heat transfer coefficient is correlated with the tip clearance, and the mean velocity is calculated by the velocity triangle method for approximation. A leakage flow region exists in the downstream direction beyond the middle of the wall surface opposite the rotor blade, and a leakage vortex is recognized at the suction side near the trailing edge. 16 refs.

Cooling Performance of an Integrated Impingement and Pin Fin Cooling Configuration

The cooling configuration adopted in this study integrates impingement cooling and pin fin cooling devices into one body, the aim being enhancement of the effective heat transfer area. The purpose of the study is to confirm improvement of cooling effectiveness for two different pin density configurations by experimental verification. Experiments were conducted in similar conditions to actual engines using large-scaled flat-plate specimens manufactured by a new rapid prototype casting technique. The results were compared with predictions by one-dimensional analysis adopting the fin efficiency theory. Although the coarse pin density, one pin in a unit area, shows good agreement with the prediction, the fine pin density, four pins in the unit area, was overpredicted. It was found by numerical analysis that heat transfer of the new pin geometry did not increase, so that its surface area increased. CFD-aided prediction was proposed and validated with two specimen’s data.Copyright

A development of a two-component velocity profiler using a fiber multi-point LDV and a CCD area image sensor

A novel method to measure two-component velocity profile simultaneously was developed by using the combined system of a CCD area image sensor and a multi-point laser Doppler velocimetry (LDV). The benefits of this method are shown by pursuing the compact and convenient over the system. Moreover, results of some measurements such as the flow field behind the cylinder shows the reliability of the measurement for turbulence fields. The basic techniques of this method are established and the applicability for the measurement of flow field is shown.

A Flow Structure at Reattachment Region of a Two-Dimensional Backward-Facing Step by Using Advanced Multi-Point LDV

A temporal data of instantaneous velocity profile of a two-dimensional backward-facing step flow was measured by multi-point LDV, and was discussed with a special focus on the details of the motion of the separated shear layer and the phenomena of reattachment. As a result, The phenomenon of reattachment was seen to follow two patterns, one when the separated shear layer reattaches, the other when the separated shear vortex reattaches. The dividing stream line oscillates because of vortex concentration in the separated shear layer and has a quasiperiodical behavior as concerned to reattachment.

Film Cooling in a Separated Flow Field on a Novel Lightweight Turbine Blade

The primary contribution of this research is to clarify the feasibility of a novel lightweight turbine blade with internal and external cooling, which is invented, aiming at drastic reduction in weight. With a considerably thinner airfoil, an extensive separation bubble is formed on the pressure side, and film cooling performance in such a flow field has to be investigated. Experimental results with a curved duct setup, which simulates the flow field around the proposed airfoil, show that a film cooling is still an effective measure of cooling even in the vastly separated region, and it behaves quite similarly to the conventional correlation, except for lower blowing ratios, where the thermal field is strongly affected by the intense recirculation flow. Comparisons between the experimental and numerical results verify that an affordable Reynolds-averaged Navier-Stokes simulation is useful to investigate the detailed physics of this flow field. With the numerical modeling, a cooling performance of the proposed blade under a typical engine operating condition is simulated, and the metal temperatures of the blade are also predicted with a fluid-solid conjugate calculation. The resultant thermal distribution in the airfoil suggests that the trailing edge portion is inevitably most critical in the temperature, and also a considerable thermal gradient across the blade is induced. Thermal profile, however, is partly recovered with some of the film coolant being bypassed from the pressure side to the suction side.

Heat Transfer and Flow Characteristics on a Gas Turbine Shroud

Abstract: The work described in this paper is an experimental investigation of the heat transfer from the main flow to a turbine shroud surface, which may be applicable to ceramic gas turbines. Three kinds of turbine shrouds are considered with a flat surface, a taper surface and a spiral groove surface opposite to the blades in an axial flow turbine of actual turbo‐charger. Heat transfer measurements were performed for the experimental conditions of a uniform heat flux or a uniform wall temperature. The effects of the inlet flow angle, rotational speed, and tip clearance on the heat transfer coefficient were clarified under on‐ and off‐design flow conditions. The mean heat transfer coefficient was correlated to the blade Reynolds number and tip clearance, and compared with an experimental correlation and measurements of a flat surface. A comparison was also made for the measurement of static pressure distributions.

Film Cooling for Slot Injection in Separated Flows

This experimental work is to investigate film cooling for slot injection in separated flows. The purpose of this research is to study the feasibility of a highly loaded very thin turbine blade which has been devised in order to reduce weight and to save the coolant amount by simplifying the complicated internal cooling passages. With such a thin airfoil, a considerable flow separation is expected to occur on the pressure-side and film cooling practice in that kind of flow field has not been well established. In order to clarify the film cooling mechanism in the separated flows, experiments with a simple back-facing step flow with a single slot injection simulating the separated pressure-side flows were carried out. Very high lip thickness to slot height ratio up to 8 was considered. Adiabatic effectiveness as well as velocity and turbulence profiles downstream of the step was measured in detail. The experimental results showed that there is a clear improvement in the film effectiveness with the largest lip thickness case for whole range of the tested blowing ratio. The flow field measurements suggested that a large recirculation zone acted as buffer or resistance for flow mixing, which contributed to the improvement in the film effectiveness.Copyright

Unsteady Flow Structure on a Heated Rotating Disk under Mixed Convection Conditions

The flow field under a mixed convection on the heated rotating disk has been measured using ultrasonic velocity profiler (UVP). The measured velocity field is a spatio-temporal one as a function of a radial coordinate and time. The objective of this paper is to clarify a vortex structure caused by instability between the buoyancy and centrifugal force. The vortex appears under typical Reynolds numbers and Grashof numbers and it moves toward outside of the disk. This behavior can be classified into two patterns. The size of the vortex structure decreases with increase in Reynolds number and increases with Grashof number. The traveling velocity of the vortex increases with Grashof number and decreases with increase in Reynolds number in spite of increase of centrifugal force. According of these results, the region dominated by natural, forced and mixed convection is classified in the relationship between Reynolds and Grashof number.

Fluid flow behavior around a circular cylinder perpendicular arrangement of circular cylinders.

Fluid flow behavior around a circular cylinder placed downstream of and perpendicular to a single row of cylinders in a uniform flow was investigated varying the distance (L) between upstream and downstream cylinders. Flow visualization techniques (oil-film and smoke-wire methods) and a near-surface flow direction judgement (flow direction probe method) were used, and time-averaged and fluctuating pressure distributions on a circular cylinder were measured under the constant Reynolds number, Re=5×104. It was clarified that the flow structure could be divided as a border of L/D=2.5. In the connection with the vortex transfer, especially, the three-dimensional separation bubble formed at L/D≤2.5 was the result of the stretching of separating shear layers due to the horseshoe-like vortex and inner secondary vortex. At this distance, the span-averaged drag of the downstream cylinder was less than 1.15 times that of a single cylinder.