Measurements of discharge coefficients in film cooling

Measurements of discharge coefficients for several film cooling configurati ons having hole length-to-diameter ratios of 2.3, 4.6, 6.6, and 7.0 are pre sented. Recently, it was documented that the velocity distributions over th e hole exit plane vary significantly with changes in hole length-to-diamete r ratio. This paper documents the effects of such variations on coolant dis charge coefficients. Due to the short holes, injection in engines is with a substantial amount of coolant departing the upstream portions of the hole exit plane. This results in a higher rate of momentum exchange with the fre e stream at that location than for longer holes, which permits more uniform exit flows. Discharge coefficient measurements are discussed in terms of t his distribution of velocity. This paper also documents the effects of the hole supply plenum geometry on discharge coefficients. When the coolant flo w is delivered to the holes with significant momentum either in the directi on of the free stream or opposite to that direction, significant changes in discharge coefficient values are observed.