Study of the influence of the number of holes rows on the convective heat transfer in the case of full coverage film cooling: Etude de l’influence du nombre de rangées de trous sur les échanges convectifs dans le cas du refroidissement par multiperforation

The protection of the combustion wall chamber of aeronautic propeller is assumed with a full coverage film cooling. In the case of 1-9 rows of eight staggered holes, we have measured several profiles of temperature in the mainstream perturbed by jets. Variations of wall temperatures T_p have been measured simultaneously along the wall. Those experiences have been performed for three thermal cases, which are a function of the mainstream temperature T_e, the injected temperature T_i and the electrical density ?_dissi. imposed at the wall. Three blowing rates M=ρ_iU_i/ρ_eU_e are imposed too. The results are compared with the reference case without holes. The exam of the temperature profiles allows us to find a minimum number of rows to create a homogeneous cold layer. Two schemes of the convective heat transfer with two coefficients are presented and allow to represent each of the three thermal cases for the three blowing rates. Those models take into account of the three characteristic temperatures (T_e, T_i and T_p). One model is studied for 9 rows with infrared thermography. For five blowing rates, four zones of variations and an influence of M on the two coefficients are underlined.