Passage Flow Structure and its Influence on Endwall Heat Transfer in a 90° Turning Duct: Turbulent Stresses and Turbulent Kinetic Energy Production

Abstract

The complex interaction between three-dimensional passage flow structure and endwall convective heat transfer in a square cross section, 90° turbulent duct flow has been experimentally investigated. Fine details of the momentum and heat transport process in a laboratory model that simulated a high Reynolds number three-dimensional passage flow are presented. The specific flow and heat transfer mechanisms are frequently encountered in the hot mainstream of axial flow turbines and internal coolant passages. Similar physical phenomena may also be observed in many other fluid machinery systems. The mean radius to duct width ratio was 2.3 and the Reynolds number based on inlet center line velocity, duct width, and ambient conditions was approximately 360,000. The complete Reynolds stress tensor was measured using a triple sensor hot wire. The turbulent normal and shear stresses, turbulent kinetic energy, and production of turbulent kinetic energy are presented. A steady state heat flux measurement technique and liquid crystal thermography were used to determine the character of the endwall heat transfer in the form of a high resolution heat transfer map. The flow field was dominated by strong counter rotating secondary flows characteristic of 90° turning ducts. The flow structure also included areas of strong streamwise accelerations and decelerations, high vorticity, local regions of significant total pressure loss, and a complex turbulent flow field structure. The development of the turbulent features of the 90° turning duct flow field and the influence of the turbulent flow field on the endwall convective heat transfer distribution are discussed. The multi-dimensional flow and high resolution heat transfer results are currently being incorporated in computational aerothermal models under development at Penn State University. The results are also available as a data base for future aerothermal model validation studies.