Gas turbines provided with free-convection cooling have rotating blades with cylindrical holes that are closed on top of the blade and connected with the fluid supply at the blade root. In the design of such blades, an important question arises as to what minimum diameter a hole of a certain length can be drilled without endangering the circulation of the cool¬ing liquid in it. An approximate answer to this problem is obtained by calculating the thickness of the heated boundary layer that builds up around the cylindrical surface of a hole with large diameter.nNumerical evaluations of the results of these calculations for a sample turbine and comparisons with test results show that in small holes such as would be required in the leading and trailing edges of turbine blades, the circulation and the cooling effect is ap¬preciably impaired. The circulation and the cooling effect in these holes can be considerably improved when a connection is provided on top of the blades between the small holes and the larger holes, which can be located in the central portion of the turbine blade.nIn the boundary-layer calculations, the effect of the Coriolis forces on the movement of the liquid in the rotating holes was neglected. The magnitude of the Coriolis forces relative to the centrifugal forces was calculated and the influence of the secondary movement set up by the Coriolis forces on the cooling effect was estimated by comparison with test results on inclined surfaces in gravitational free-convection heat transfer.
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