Effect of bleed position and bleed angle on impingement cooling of a spherical-dimpled surface

Numerical simulations were performed to document cooling of the lower surface of a channel. Through the channel top wall and normal to the channel flow are cooling jets that impinge on the channel lower surface. This surface has a regular array of dimples with centers in line with the impingement jet axes. Also on the channel lower surface is a series of purge holes through which coolant flow is extracted. The effects of location of the purge holes relative to the dimples and angle of the purge holes on the channel lower surface cooling performance are documented. A 3D RANS analysis with SST k-ω turbulence closure modeling was conducted with a Reynolds number of the impingement jet of 35,000. The position of the purge hole relative to the dimple was varied from-0.34 to 0.50 dimple spacing, the purge hole angle varied as 30° and 150° and three different ratios of bleed flow rate to impingement jet flow rate, 2.5%, 5.0% and 12.0%, were documented. The results show how the combined effects of impingement jet flow, channel crossflow and purge flow affect heat transfer characteristics on the channel lower surface for this assembly. Also shown is how the dimpled surface heat transfer benefits from putting the purge flow holes slightly upstream in the channel flow from the dimples. The geometry under study may be applied for cooling a gas turbine endwall, where the bottom side of the channel lower wall of the assembly under study would be the passage endwall and the purge flow would be discrete hole film cooling flow.