Arvind Pattamatta

Film cooling methodologies in air-breathing gas turbines have been evolving for many decades. In the present work, a combined experimental and numerical parametric study is conducted to investigate the three-dimensional slot film cooling of an annular combustor. The experimental investigation is conducted to understand the fluid flow and heat transfer phenomenon of the film cooling and to validate the numerical study under laboratory conditions (low temperature and pressure). Transient infrared thermography is used to estimate both adiabatic film-cooling effectiveness (ηad) and heat transfer coefficient (h) simultaneously using a semi-infinite approximation method. The blowing ratios considered in the study are in the range of 0.5 to 5. The experimental results showed that film-cooling effectiveness (ηad) enhanced with an increase in the blowing ratio from 0.5 to 2 and deteriorated beyond BR = 2 due to the adverse effects of turbulence. A parametric study is conducted numerically to understand the effect of flow and geometrical parameters under actual engine conditions (high temperature and pressure). The parameters considered are slot Reynolds number (Res), slot jet diameter (d), slot jet pitch (p), lip taper angle (α), lip length (L), and slot jet injection angle (β). For the considered parameters, numerical results showed that the slot jet diameter (d) = 2 mm, dimensionless slot jet pitch (p/d) = 2, slot jet injection angle (β)=20o and dimensionless lip length (L/d) = 5.9 outperformed the other configurations due to the low turbulence and entrainment. Finally, an Artificial Neural Network-based mathematical model is developed that correlates the ηlat as a function of flow and geometrical parameters.

This paper reports the results of experimental and numerical studies to understand the heat transfer characteristics of three-dimensional wall jets exiting from a single and a row of circular jet openings over an unheated flat plate. Infrared thermography is employed to obtain the temperature distribution over the target surface, and the semi-infinite approximation methodology is used to estimate the heat transfer coefficients. Single wire constant temperature hot-wire anemometer is used to measure the flow characteristics. Additionally, computational studies have been performed to select a suitable low Reynolds number turbulence closure models among the following models, namely (i) Spalart Almaras (SA) (ii) Realizable k-ε with enhanced wall treatment (RKE-ewt) (iii) k-ω SST and (iv) Reynolds Stress Model with enhanced wall treatment (RSM-ewt) that predicts the experimentally obtained results for heat transfer characteristics accurately. Based on the investigations carried out, it is observed that RKE-ewt turbulence closure model is not only accurate but also faster in the prediction of heat transfer coefficient. Further, it is also seen that for a fixed mass flow rate, and at a given diameter of the jet opening, widely spaced jets show higher heat transfer coefficients. Furthermore, for a row of three-dimensional wall jets correlations based on the numerical results are developed for the Nusselt number for a Reynolds number range of 5000 to 15000.