Experimental investigation on impingement/effusion cooling with short normal injection holes

An experimental investigation on cooling performances of integrally impingement/effusion cooling configurations with film cooling holes angled normal to the mainstream flow is conducted. The adiabatic film cooling effectiveness and the overall cooling effectiveness are measured on a polycarbonate test plate and a stainless steel plate respectively. Effects of the blowing ratio (ranged from 0.6 to 2.4), multi-hole arrangement (inline and staggered), hole-to-hole pitch ratio (ranged from 3 to 5) and jet-to-target spacing ratio (ranged from 2 to 4) on the cooling performance are examined. In addition, jet impingement heat transfer is measured to evaluate the dense array jet impingement behaviors with local extraction of coolant via effusion holes. A new parameter named corrected blowing ratio is introduced in the present to evaluate the cooling effectiveness for different effusion or impingement–effusion configurations under a given quantity of cooling air. In an integrally impingement–effusion cooling configuration, multiple jet impingement with local extraction of coolant via effusion holes is able to produce higher overall heat transfer under lower jet-to-target spacing and denser jet array. The action of additional jet impingement heat transfer on improving overall cooling performance is highly dependant on the blowing ratio, multi-hole arrangement and jet-to-target spacing, which seem to be behaved superior in the situations where the film cooling effect isolating the wall surface from the hot mainstream is weak. For an integrally impingement–effusion cooling configuration, the densest hole-to-hole array is favorable in the situations where the coolant mass flow rate per unit area of cooled surface is low. As the coolant mass flow rate per unit area of cooled surface increases, the hole-to-hole pitches could be gradually enlarged to make effective utilization of array jet impingement.