Experimental study of convective heat transfer due to the development of a cold film air
Our work focuses on the technique of film cooling used, for example, for cooling wall of the combustion chamber. This study consists of two parts: The first part consists of an experimental study on the film cooling in conditions of low temperature: 40°C for the mainstream flow and 20°C for the coolant flow. The blowing ratio M ranges from 1 to 4. The test rig consists of a plate with 81 injection holes inclined at 30° with respect to the surface of the plate. The first, we study the influence of blowing ratio M and the influence of the opening of the rows of holes on the formation of the film cooling. This first step has determined a base configuration. This configuration corresponds to the minimum required number of rows of holes for the formation of the film cooling. The second, we studied the influence of two geometric parameters on the film cooling: the inter-holes distance p/D = 4, 8, 12 and the inter-rows distance s/D = 4, 8, 12. The results showed that increasing of the spacing between injections leads to the decrease of the adiabatic effectiveness of film cooling and the decrease of the heat transfer coefficient. The last, the goal of our work is to optimize the maintenance of the cooling layer. For this, we proposed adding a further injection pattern following the basic configuration. Thus, we found that the opening of one additional row improve the cooling effectiveness whatever the position of the adding row of holes is from the base configuration. On the other hand, the opening of three additional rows gives significant improvements of the adiabatic effectiveness of film cooling. We have noted better maintenance of the film cooling by adding rows adjacent to the base configuration. The second part is devoted to studies of cooling on a virtual test bench industrial bench called Thalie. This test bench allows to reproduce conditions similar to those aero-thermal encountered in a combustion chamber (temperature up to 1400K and pressures up to 7.10 5 Pa). However, these extreme conditions do not allow the direct application of the experimental techniques developed in the conditions of lower temperature and pressures. Therefore, the objective of this experimental part is to conduct a feasibility study on a new measurement technique. For this, a technique for measuring transient is proposed. The principle of this method is to impose a level of temperature on the primary flow and monitor the temperature field of the wall. The heat transfer coefficients between the wall and flows are identified by minimizing the difference between the wall temperature measured by infrared thermography and the one calculated by solving the equation of heat transfer.