Enhanced Internal Heat Transfer on the Tip-Wall in a Rectangular Two-Pass Channel (AR = 1:2) by Pin-Fin Arrays

Abstract

To improve gas turbine performance, the operating temperature has been increased continuously. However, the heat transferred to the turbine blade is substantially increased as the turbine inlet temperature is increased. Cooling methods are therefore much needed for the turbine blades to ensure a long durability and safe operation. The blade tip region is exposed to the hot gas flows and is difficult to cool. A common way to cool the tip is to use serpentine passages with a 180 turn under the blade tip cap taking advantage of the three-dimensional turning effect and impingement. Increasing internal convective cooling is however required to increase the blade tip life. In this article, enhanced heat transfer of a blade tip has been investigated numerically. The computational models consist of a twopass channel with a 180 turn and arrays of pin-fins mounted on the tip-cap, and a smooth two-pass channel. Inlet Reynolds numbers range from 100,000 to 600,000. The computations are 3-D, steady, and incompressible. The detailed 3-D fluid flow and heat transfer over the tip surfaces are presented. The overall performance of the two models is evaluated. It is found that due to the combination of turning, impingement, and pin-fin crossflow the heat transfer coefficient of the pin-finned tip might be a factor of 1.84 higher than that of a smooth tip. This augmentation is achieved at the expense of a penalty of pressure drop around 35%. It is suggested that the pin-fins could be used to enhance blade tip heat transfer and cooling.

Numerical predictions of augmented heat transfer of an internal blade tip-wall by hemispherical dimples

“…The turbulent heat transfer in the smooth two-pass channel has been computed [29]. The local calculated Nusselt number results agree with the experimental data of Bunker [28] with an acceptable accuracy.…”

“…Regarding this consideration, it is recommended that dimples can be effectively designed to enhance the tip heat transfer and hence improve tip cooling at low Reynolds numbers. Smooth-tip Case I, this work Case II, this work Pin-finned-tip, [29] Al pins, H=8,13mm, [25] (Nu/Nu s )/(A/A s ) Re Fig. 13.…”

“…Therefore, the agreement between the calculated Nusselt number and experimental data is the main criterion for selecting a turbulence model. In previous works, several turbulence models have been evaluated to simulate the turbulent heat transfer of a smooth-tip two-pass channel [29][30][31]. Based on those evaluations, the Realizable k À e turbulence model is selected for the computations in this work.…”

“…Even though similar works of the heat transfer augmentation in two-pass channels with shaped pin-finned tips can be found in the experimental work by Bunker [28] and the numerical simulations by the authors [29][30][31][32], no available details of the heat transfer and flow field on dimpled tips are available. Furthermore, most previous studies were concerned about the heat transfer on the leading or/and trailing walls of two-pass channels, and very limited information is available for tip-walls.…”

Heat Transfer Research in Sweden: Historical and Current Activities

“…The most recent work on tip cooling of gas turbine blades have received good recognition [41][42][43].…”