Second law analysis of aerodynamic characteristics with flow temperature variations of simple angle and compound angle full coverage film cooling

Abstract

The present investigation employs entropy generation to quantify aerodynamic characteristics with flow temperature variations, and the associated second law losses, which are present within a film cooled boundary layer produced by a unique full-coverage compound angle hole configuration. With this arrangement, an alternating sign for the compound angle β is employed from one streamwise row of holes to another, such that compound angle β is +30° in one row of holes, followed by −30° in the next row of holes. Entropy change distributions, entropy generation distributions, and mass-averaged overall exergy destruction from this compound angle arrangement are compared to results from a simple angle arrangement with β = 0°. These quantities are determined from flow field measurements of local flow temperature variations, and local stagnation pressure variations with film cooling. Within the investigation, full-coverage film cooling blowing ratio values range from 2.9 to 6.0, mainstream Reynolds numbers Rems range from 127,000 to 142,000, and effusion flow Reynolds numbers range from about 7000 to approximately 13,000. Distributions of local entropy generation and mass-averaged overall exergy destruction (both relative to freestream flow) are determined using three analysis approaches, which account for local flow temperature variations only, local flow stagnation pressure variations only, and variations of stagnation pressure and local flow temperature together. Similar qualitative trends of local entropy generation for the three different types of data are observed, which mean that temperature and stagnation pressure within the flow experience similar rearrangements by secondary advection and diffusion phenomena for the two film cooling arrangements. From a quantitative perspective, values associated with flow temperature variations only, are consistently larger than values associated with stagnation pressure variations only. Important local variations of local entropy generation are observed for the compound angle arrangement, which are due to skewed and non-symmetric film distributions, along with the associated tilted horseshoe-shaped vortex, which forms around each film coolant concentration.