Experimental and numerical investigation of air flat-plate film cooling with mist injections for different film hole shapes

The behavior of turbulent flow and heat transfer on an air film-cooled flat plate with mist injections at varying spray pressures, having a varying mist proportion and nonuniform distribution of droplet diameter, was experimentally and numerically studied. Using the Infrared thermometry technique and hot-film heating coating, the adiabatic film cooling effectiveness (FCE) and heat transfer coefficient (HTC) distributions were assessed under different spray pressures (5 MPa ≤ P_s ≤ 9 MPa) and blowing ratios (1.0 ≤ M ≤ 2.0), and a detailed comparison of both spanwise- and area-averaged FCE between the cylinder, laid-back, and laidback fan-shaped holes cases, was presented. The two-parameter Realizable k-ε turbulence model with a phase-coupled Lagrangian stochastic tracking method was used to simulate the flow structures, thermal field, and droplet dynamics at various M and shapes of film holes. The results show that the laidback fan-shaped hole case with streamwise and spanwise expansions provides the highest FCE among the three cases, maintaining a remarkably high value at every M . Mist greatly enhances the air FCE of three types of film holes, and its FCE enhancement ratio related the spray pressure and M . A stable of about 30%-70% improvement is achieved for the LFH case under all the spray pressures and M due to the reduced the kidney vortex intensity and droplet evaporation. At P_s = 7 MPa, the HTC of the mist/air film cooling for the cylinder hole decreases monotonically and gradually stabilizes at a certain value. The maximum enhancement ratio of area-averaged HTC is reached at 13% at M = 1.3.