Heat transfer and friction factor in a dimple-pin fin wedge duct with various dimple depth and converging angle

Abstract

Purpose – The dimple is adopted into a pin fin wedge duct which is widely used in modern gas turbine vane cooling structure trailing edge region. The purpose of this paper is to study the effects of dimple depth and duct converging angle on the endwall heat transfer and friction factor in this pin fin wedge duct. Design/methodology/approach – The study is carried out by using the numerical simulations. The diameter of dimples is the same as the pin fin diameter with an inline manner arrangement in relation to the pin fin. The ratio between dimple depth and dimple diameter is varied from 0 to 0.3 and the converging angle is ranging from 0° to 12.7°. The Reynolds number is between 10,000 and 50,000. Results of the endwall Nusselt number, friction factor, and flow structures are included. For convenience of comparison, the pin fin wedge duct with a converging angle of 12.7° without dimples is considered as the baseline. Findings – It is found that the dimples can effectively enhance the endwall heat transfer due to the impingement on the dimple surface, reattachment downstream the dimple and recirculation in front of the pin fin leading edge. By increasing the converging angle, the heat transfer is also increased but with a large friction factor penalty. In addition, the heat transfer enhancement for deep depth cases is 1.57 times higher than that of the low depth case. The thermal performance indicates that the intensity of heat transfer enhancement depends upon the dimple depth and converging angle. Originality/value – It suggests that the endwall heat transfer in a pin fin wedge duct can be increase by the adoption of dimples. The optimal dimple relative depth is 0.2 with low friction factor and high heat transfer performance.

Surface temperature reduction by using dimples/protrusions in a realistic turbine blade trailing edge

“…Figure 9 illustrates the heat flux contours on the endwall for the dimples and protrusions with different layouts. A continuous and significant increase of the heat flux value occurs along the streamwise direction which can be related to the flow acceleration effect of the converging duct [21]. The heat flux distributions around the pin fins are obviously higher for the side-by-side arrangement than for the upstream one, and higher for the upstream compared with the downstream arrangement for both dimples and protrusions.…”

“…Rao [20] tested the dimple depth effect on the pressure loss and heat transfer characteristics in a pin fin-dimple channel, where dimples were located between the pin fins and revealed the underlying mechanisms by associating the velocity, and temperature distributions with the pressure loss, and heat transfer together at Reynolds number changing from 8,200 to 50,500. Luo [21] further simulated the dimple depth and converging angle contributions to the heat transfer and friction factor on a dimpled pin-fin wedge duct and concluded that the dimple case with 0.2 relative depth showed the best heat transfer performance at 12.7 converging angle. However, a deeper dimple with larger converging angle provided a better thermal performance.…”

Heat Exchange Between Air and a Liquid Film Flowing Down Along a Profiled Surface

“…In the literature, one can find numerous works devoted to the intensification of heat exchange between a solid surface and a liquid flow along it due to the formation of indentations -dimples on the surface [1][2][3][4][5][6][7][8][9][10]. It was established that such surface profiling leads to the generation of non-stationary vortex structures in the flow, mixing of the liquid, and, as a result, noticeable intensification of heat exchange as compared with a smooth surface.…”

Heat transfer characteristics of a dimpled/protrusioned pin fin wedge duct with different converging angles for turbine blades

“…Other researchers [16][17][18][19][20] also have performed experimental and computational studies on the dimple shape, dimple depth, and dimple configuration. Luo et al [21][22][23][24] used numerical methods to study the effects of dimple arrangements, dimple depth, and converging angle on the heat transfer and flow structure in a pin fin channel/duct. The results of the dimple-pin fin channel showed a tremendous heat transfer augmentation performance.…”