Studying the Vortex Heat Transfer Enhancement during Turbulent Air Flow over a Plate with a Limited Package of Inclined Oval-Trench Dimples Using Numerical Modeling and Gradient Heatmetry

Abstract

The article presents a numerical and experimental study of separated flow and heat transfer in limited packages of four inclined oval-trench dimples (OTDs) located on a heated isothermal section of an adiabatic plate in uniform air flow with the Reynolds number Re = 3 × 10⁴. The depth of dimples is equal to 0.25 of their width, and the angle of inclination is 45°. The isothermal section temperature is maintained with saturated steam. The results of numerical calculations carried out by solving the Reynolds averaged Navier–Stokes equations in the VP2/3 software package, which are closed by the differential equations of the shear stress transfer model (RANS with the SST turbulence model) and the equation of energy, were validated by comparing them with the experimental data obtained by means of gradient heatmetry techniques on the thermophysical setup at the St. Petersburg Polytechnic University. Multiblock computation technologies with the use of intersecting meshes of different scales were applied. It has been found that, with shifting the dimples away from the plate leading edge, relative heat transfer coefficient and back flows are enhanced. With a shift from the first to the fourth dimple, the relative Nusselt number increases in the inlet parts at the bottom by a factor of two (from 1.2 to 2.4) and by a factor of 1.7 (from 1.5 to 2.6) in the windward edge area. The stabilization of stagnation pressure on the windward slopes at a level of 0.26 with the minimal pressure equal to −0.15 in the vortex generation zones entails enhancement of back flows. The static pressure differences cause enhancement of back flows in packaged dimples. The study results have revealed fundamental differences in the heat transfer distribution between the first and subsequent dimples, as well as in their end parts.