FLOW PATTERN AND HEAT-TRANSFER IN A CLOSED ROTATING ANNULUS

The prediction of the temperature distribution in a gas turbine rotor containing gas-filled closed cavities, for example between two disks, has to account for the heat transfer conditions encountered inside the se cavities. In an entirely closed annulus no forced convection is pre sent, but a strong natural convection flow occurs induced by a nonunif orm density distribution in the centrifugal force field. A computer co de has been developed and applied to a rotating annulus with square cr oss section as a base case. The co-axial heat flux from one side wall to the other was modeled assuming constant temperature distribution at each wall but at different temperature levels. Additionally the inner and outer walls were assumed to be adiabatic. The code was first veri fied for the annulus approaching the plane square cavity in the gravit ational field, i.e., the ratio of the radius r over the distance h bet ween outer and inner cylindrical wall was set very large. The results obtained agree with De Vahl Davis' benchmark solution. By reducing the inner radius to zero, the results could be compared with Chew's compu tation of a closed rotating cylinder, and again good agreement was fou nd. Parametric studies were carried out varying the Grashof number Gr, the rotational Reynolds number Re, and the r/h ratio, i.e., the curva ture of the annulus. A decrease of this ratio at constant Gr and Re nu mber results in a decrease of heat transfer due to the Coriolis forces attenuating the relative gas velocity. The same effect can be obtaine d by increasing the Re number with the h/r ratio and the Gr number bei ng constant. By inserting radial walls into the cavity the influence o f the Coriolis forces is reduced, resulting in an increase of heat tra nsfer.