Hole Exit Velocity Measurements in Film Cooling Flows

The mean velocity profiles at hole exit have been found to be highly sensitive to the film cooling length. Film cooling with short holes (L/D=2.3 in figures) tends to have a great deal of its coolant mass distributed towards the upstream portion of and along the edges of the hole at the exit plane. At entrance to the hole, a separation bubble forms that causes this malproportioned coolant mass distribution.

Film cooling through long lengths (L/D=7.0 in figures) though is characterized by more uniform profiles or those slightly favoring the downstream portion of the hole at exit.

The disturbance at hole entrance found with short-hole cases is also present but is attenuated by the additional hole length. The allows the flow to recover to a more "fully-developed" or parabolic exit flow. The coolant-to-freestream blowing rate, and associated coolant momentum, influences the exit profiles as well. Hole exit mean velocity (Ulocal/Ubulk) profiles for film cooling through short and long lengths (L/D=2.3 a nd 7.0) and at low and high (VR=0.5 and 1.0) blowing rates are provided below.

Low Blowing Rate (VR=0.5):

Hole Exit Profile Hole Exit Profile

High Blowing Rate (VR=1.0):

Hole Exit Profile Hole Exit Profile
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