Heat Transfer, Pressure Drop, and Mass Flow Rate in Pin Fin Channels With Long and Short Trailing Edge Ejection Holes

Abstract

Experiments have been conducted to study the turbulent heat transfer and friction characteristics in pin fin channels with small trailing edge ejection holes that are commonly found in modern internally cooled turbine airfoils. The main objective of the investigation is to examine the effects of varying the length and the configuration of the trailing edge ejection holes on the overall heat transfer, the overall pressure drop, the local pressure distribution, and the local mass flow rate distribution in the pin fin channel. The staggered pin fin array (L/D = 1.0, X/D = S/D = 2.5) in the test channel has 15 rows of three pins. The diameter of the ejection holes is one-half the diameter of the pins. There are 30 or 23 ejection holes on one of the side walls of the test channel and six similar ejection holes at the radial flow exit. Experimental results are obtained for two trailing edge ejection hole lengths, four ejection hole configurations, and Reynolds numbers between 10,000 and 60,000. The results show that the overall heat transfer increases when the length of the trailing edge ejection holes is increased and when the trailing edge ejection holes are configured so that much of the cooling air is forced to flow farther downstream in the radial flow direction before exiting the pin fin channel through ejection holes. The overall Nusselt number can be correlated with an equation of the form NuD = a (ReD )b , where the values of the exponent b are about the same for all the test cases with trailing edge flow ejection. Results also show that the increase in the overall heat transfer is generally accompanied by an increase in the overall pressure drop (that is, an increase in the required pumping power), except that the overall heat transfer is lower and the overall pressure drop is higher when there is no radial flow ejection. In the cases with both radial and trailing edge flow ejection, about 15 to 20 percent of the flow exits through the tip bleed holes.