Project Summary

The objective of this three-part investigation is to provide industry with much needed heat transfer data to assist the designers in improving the cooling performance and thermal efficiency of power generation and industrial turbine engines. More specifically, this investigation ventures into the heat transfer phenomenon of internal cooling channels near the trailing edge of a turbine blade, which has yet to be reported in detail. The research is divided into three parts: Part I - Rotating Heat Transfer; Part II - Stationary Heat Transfer; Part III -Numerical Prediction. This investigation is a collaboration between Dr. J.C. Han and Dr. H.C. Chen of Texas A&M University and Dr. Phil Ligrani of the University of Utah. This report details the second stage of this investigation, namely the channel of aspect ratio AR = 4:1. This investigation also concerns heat transfer investigations into a channel of AR = 8:1 to be completed subsequent to the 4:1 investigation presented in this report. A more detailed breakdown of the investigation of each of the three parts follows.

Part I - Rotating Heat Transfer:

The objectives of part I are to obtain experimental data from rectangular, internal cooling passages with aspect ratios of 4:1 and 8:1. The following parameters will be varied: (1) Surface geometry (2) Reynolds number, (3) rotation number, (4) rotation angle, and (5) channel aspect ratio. Ribs, pins, and dimples will be installed on the leading and trailing sides of a rectangular internal cooling passage with rotation. The ratio of inlet coolant temperature to surface temperature (TR) will be around 0.8 - 0.9. The experiments is designed so that regionally averaged heat transfer coefficients will be measured at different locations along the cooling passages under rotating conditions. Both the streamwise and spanwise distribution of the heat transfer enhancement will be obtained. The new heat transfer data will be correlated and compared with numerical predictions in part III. The existing rotating facility and instrumentation available in the Turbine Heat Transfer Laboratory of Texas A&M University is used in this study.

Part II - Stationary Heat Transfer and Flow Field:

The objectives of Part II are to obtain experimental data from rectangular, internal cooling passages with aspect ratios of 4:1 and 8:1. The following parameters will be varied: (i) surface geometry, (ii) ratio of absolute inlet temperature to wall temperature, (iii) Reynolds number, and (iv) channel aspect ratio. Ribs, pin fins, dimples and smooth surfaces will be installed on the surface of a rectangular internal flow passage (without rotation). The ratio of inlet coolant temperature to surface temperature (TR) will range from 0.6 to 1.0. The experiments will be designed so that: (a) spatially-resolved surface heat transfer coefficients will be measured at different location along the instrumented surface which contains the concavities, and (b) detailed flow structure above the different surface configurations will be measured using existing five-hole pressure probes, flow visualization apparatus, and pressure transducer equipment. Spatially-averaged data will be deduced from the spatially-resolved data. The flow structure data will aid numerical model development in Part III. Two existing test facilities, available in the Convective Heat Transfer Laboratory of the University of Utah, are employed.

Part III - Computational Study:

The objectives of part III are to predict flow and heat transfer behaviors from rectangular, internal cooling passages with aspect ratios of 4:1 and 8:1. An ongoing Chimera Reynolds-Averaged Navier-Stokes (RANS) code together with an advanced state of the art second-order Reynolds stress (second moment) turbulence model will be used for the prediction of rotating and stationary rectangular cooling channels with ribs, pins or dimples. The present numerical model has been tested to provide much better flow and heat transfer predictions than the standard k-e turbulence model for rotating multi-pass square channels. The numerical predictions will be calibrated/compared with the part I-rotation at TR = 0.9 and with the part Il-stationary at TR = 0.6. The ultimate goal is to predict flow and heat transfer in rotating rectangular channels with ribs (pins or dimples) at very high Reynolds number and buoyancy parameter conditions.

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