Turbulent Flow and Heat Transfer in a Rotating SquarernDuct with Scale-Like Cavities on Two Opposite Walls

摘要

Modern advanced gas turbine blades are subjectedrnto high thermal stress due to increasing operatingrntemperature. Consequently, efficient internal coolingrntechniques such as film cooling and internal cooling [1]rnare required to maintain allowable blade temperaturesrnand acceptable blade durability. The heat transferrncharacteristics in the internal coolant channels of gasrnturbine blades are affected by the geometries of channelrncross-section, turbulators, dimples [2], rotation, etc.rnPrevious researches mainly focus on heat transferrnaugmentation with rib turbulators. Nonetheless, thernrecent study of dimples has drawn new interests [3].rnIn the present study, numerical studies of turbulentrnflow and heat transfer in a rotating square duct withrnscale-like cavity dimples on two opposite walls arernperformed. The Reynolds number (Re), based on channelrnhydraulic diameter and bulk mean velocity, is fixed atrn10000 and the rotation number (Ro) ranges from 0 to 0.2.rnTurbulence closure associated with 3-D steady-staternincompressible Reynolds-averaged Navier-Stokesrn(RANS) equations was attained by simultaneouslyrnsolving Reynolds Stress Equations [4]. The ReynoldsrnStress Model (RSM) can respond to the effects ofrnstreamline curvature and anisotropy without the need forrnexplicit modeling. Enhanced wall treatment is adopted tornresolve the near wall region. The convection andrndissipation term are discretized with second-orderrnupwind and central difference scheme, respectively.rnComputed results are presented in terms of Nusseltrnnumber contours, secondary flow patterns, and near wallrnhelical flows for stationary (Ro = 0.0) and rotating (Ro =rn0.2) conditions. In stationary condition, the main flowrnand heat transfer are symmetric, and the secondary flowrnpatterns and helical flows (spring-like structures) near thernwall are induced by Reynolds stress anisotropy andrndimple. As Ro increases from 0 to 0.2, the main flow isrnskewed to the trailing wall and a counter-rotating vortexrnpair pattern is formed because of Coriolis force.rnMoreover, the helical flow near the trailing wall isrnenhanced by rotation. The near wall helical flowrnaugments the wall heat transfer, especially the trailingrnwall.