Goals

The proposed research deals with flow and heat transfer in rotating channels. This configuration is of interest in internal cooling of gas turbine blades. Efforts directed toward improving the performance of gas turbine engines through increased turbine inlet temperatures require a clear understanding of the flow and heat transfer mechanisms under rotational conditions, and for parameters relevant to actual gas turbine engines. These parameters include aspect ratio and shape of the coolant channel, the channel orientation relative to the rotational axis, the Reynolds number (Re=UDh/v) , the Rotation number (Ro=W Dh/U) and the centrifugal buoyancy parameter (BP=Ro2(R/Dh)(Tw-T)/Tw). The majority of the published literature deals with square or 1:2 aspect ratio channels, and the majority of the data published is for buoyancy parameters less than 1. However, the coolant passages in turbine blades can have aspect ratios of the order of 1:4 (along the leading edge) and 4:1 along the trailing edge, and buoyancy parameters can be considerably higher than that reported in the literature. The present work will experimentally investigate heat transfer in high/low aspect ratio channels (1:4 or 4:1) with different orientations (relative to the rotational axis) for Reynolds number up to 500,000, Rotation number up to 1, and buoyancy parameter values up to 5. These measurements will be done in a rotating rig donated by UTRC, with instrumented test sections that will befabricated or modified. Details of the velocity field, and further extensions of the above parameters (triangular leading edge cross-sections, Reynolds number up to a million, and buoyancy parameters up to 10) will be done using a validated CFD code.

The main goal of the proposed research is to provide the relevant data for parameter ranges relevant to engine operating conditions, and to provide an understanding under these conditions, of the flow and heat transfer mechanisms in a rotating coolant channel. A two-pass smooth and ribbed rotating channel (normal and angled trips) will be studied. Time-resolved heat transfer measurements in the rotating frame and computations are proposed to address the goals of the research. The heat transfer measurements will be made in a facility obtained from UTRC. Provisions are available for both thermocouple based heat transfer and liquid-crystal based heat transfer measurements. These measurements will be done under conditions of rotation, for Reynolds number, Rotation number and centrifugal buoyancy parameter relevant to gas turbine applications. Pressure drop measurements will also be performed to provide information on the thermal performance behavior. The calculations will involve the solution of the Reynolds-Averaged Navier-Stokes (RANS) with a validated turbulence model. The model validation will be performed primarily through comparisons with measurements.

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