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Rotating machinery like gas turbine engines consist of rotating components like gas turbine disks that are exposed to high thermal loads and stresses due to centrifugal force acting on them, and thus effective cooling is essential. The disks are additionally exposed to hot turbine gas ingress as an adverse pressure gradient is created in the stator-rotor cavity due to outward pumping of near-disk flow. Impingement of a coolant jet on such a surface can effectively provide cooling and also counter this adverse gradient. There also exists a circular relative velocity between the disk and wall-jet formed by impinging air as well as the air in the disk vicinity. Thus, the study of heat transfer under rotating conditions becomes important. With the advent of advanced manufacturing techniques, it is possible to produce disks with novel heat transfer enhancement features such as pin-fins which have not been previously explored. They create unique flow features in addition to increasing the surface area. The present study numerically investigates the heat transfer over rotating surfaces under jet impingement with square, triangular, cylindrical and dome-shaped pin-fins. This will inform the optimization of pin geometry for better heat transfer effectiveness and uniformity. Three different jet Reynolds numbers between 5000 and 18000 based on the jet diameter have been studied for three different Rotational Reynolds numbers based on the disk diameter. Transient non-conjugate heat transfer analysis was conducted, and the technique was compared with experimental results on square pin-fins and a smooth circular disk. The heat transfer enhancement greatly depends on the flow separation and pin area normal to the flow. A heat transfer enhancement of close to 2.2 was observed for triangular fins for the lowest rotation speed, for the highest rotation speed, the highest enhancement of close to 1.7 was observed in the cylindrical pins. [ABSTRACT FROM AUTHOR]

Many engineering applications consist of rotating components that experience high-heat load. Applications like the gas turbine engine consist of rotating disks and the study of heat transfer over such rotating surfaces is of particular interest. In the case of gas turbines, the disk also needs to be protected from the ingress of hot turbine gases caused by the low-pressure region created due to the radially outward pumping of fluid close to the rotating surface. The present experimental study investigates the effects of introducing pin-fins on heat transfer over surface of a rotating gas-turbine disk. The experiments were conducted at rotational Reynolds numbers (⁠ReR⁠) of 5487-12,803 based on the disk diameter (⁠D⁠) and jet Reynolds numbers (Re) of 5000-18,000 based on the jet diameter. The effects of nozzle to target spacing (⁠z/d=2-6⁠), eccentricity of impingement (⁠ε = 0-0.67⁠), angle of impingement--both toward and away from the center (⁠θi and θo=0 deg-20 deg⁠), and the pin fin height (⁠Hf=3.05 mm-19.05 mm⁠) were studied. Steady-state temperature measurements were taken using thermocouples embedded in the disk close to the target surface, and area average Nusselt number (⁠Nu⁠) was calculated. The results have been compared with those for a smooth aluminum disk of equal dimensions and without any pin-fins. The average Nu was significantly enhanced by the presence of pin-fins. The enhancement was higher for lower values of Re⁠, and the maximum enhancement was found to be 3.9 times that of a smooth disk for Re=5000⁠. In the impingement dominant regime, the effect of disk rotation was minimal for a smooth disk, but the heat transfer increased with rotational speed in case of pin-fins. There was no impact of eccentricity on Nu for ε = 0 and 0.33⁠. For ε = 0.67⁠, the maximum reduction in enhancement over a smooth surface (21.95%) was observed when compared with coaxial impingement for stationary impingement for Re=18,000 and z/d=4⁠. The effect of inclination angle was insignificant, and no clear trend could be established. Higher heat transfer rates were observed for z/d=6 with the increasing Re⁠, and this effect diminished with the increase in the rotational speed. With the increase in pin-fin height, especially at higher values of Re⁠, there was in increase in the value of Nu. Qualitative visualization of flow field has been performed for smooth and the pin-fin case using the commercial simulation package Ansys Fluent to further understand the flow features that result in the heat transfer enhancement. [ABSTRACT FROM AUTHOR]