Jet-impingement heat transfer is commonly used for vane leading edges and endwalls of turbine passages for cooling the surfaces. One of the factors that limit high heat transfer rates is the effect of the crossflow which builds up downstream and adversely impacts the jet penetration and the impingement heat transfer rates. The present paper investigates a concept of introducing return holes for the crossflow to prevent its build up and therefore reduce its deleterious effects. 

 In the present experimental study, a 3 by 9 jet-array impinging on a target surface is considered with and without return holes. The return holes are located in an in-line pattern between the impingement holes. Experiments are conducted for a jet hole diameter of 9.5 mm,  jet to target distances (H/D) of 1D to 12D and Reynolds number (UD/n) in the range of 15,000 to 25,000. Three different exhaust configurations with or without return holes of different diameters (D, 0.7D and 0.3D) are studied. A transient liquid-crystal based study is conducted using a thin sheet of narrow band Thermochromic Liquid Crystal (R35C1W, LCRHallcrest) glued on an acrylic plate serving as the target surface. Local heat transfer coefficients are obtained based on the measured surface temperature and the solution of 1D transient heat conduction in the target acrylic plate. 

For H/D≤4 without return holes, significant attenuation effects of the crossflow on the stagnation and area-averaged heat transfer is observed from jet 7 to jet 9. For these downstream jets, regions of high heat transfer associated with the stagnation region shrinks by up to 23% both in the spanwise and the streamwise directions. For cases with 1D-open return holes, the averaged-heat transfer is enhanced up to 19% for H/D=1 due to reduction of the crossflow-induced reduction of the impingement heat transfer. Significantly greater enhancements in the local values are observed. For the 0.7D and 0.3D return hole cases, the corresponding area-averaged enhancements are lower and are 11% and 8% respectively.  For higher jet to target distances (H/D>4), the effect of the crossflow is weaker due to larger channel cross section area and the heat transfer coefficients are similar for all the cases.  


Impingement Heat Transfer From a Jet-Array With In-Between Return Holes for the Crossflow

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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