Analytical Investigations of Rotating Disks With and Without Incorporating Rotating Heat Pipes

Abstract

The temperature limitation is one of the most crucial limiting factors to the efficiency of military gas turbine engines. An increased turbine inlet gas temperature decreases both specific fuel and air consumption while increasing efficiency. This desire for a high turbine inlet gas temperature, however, is often in conflict with materials available to withstand this high temperature. For example, the maximum disk rim temperature of some advanced development engines would exceed 1000°C, which is approaching the creep limitation of the commonly used disk materials, such as an Inconel. A literature survey regarding the turbine disk cooling reveals that although the average air-cooling heat transfer coefficient is generally high, the local heat transfer coefficient at the disk rim is relatively low. Based on the understanding that one of the major causes of the high disk rim temperature is the low thermal conductivity associated with the turbine disk material (on the order of 20 W/m-K), the concept of cooling the disk by employing the heat pipe cooling technique was proposed (Cao et al. 1). With the incorporation of the heat pipe, the effective heat dissipation area of the disk is substantially increased and the problem associated with the accumulation of the excessive heat at the disk rim is alleviated. The proposed disk with the heat pipe was numerically analyzed with excellent results (Cao et al. 2). In this paper, closed-form analytical solutions are sought for turbine disks cooled through both the conventional air-cooling and heat pipe cooling techniques. The closed-form solution has the advantages of simplicity and convenience for practical design of a turbine disk employing a specific cooling technique. The solutions could also be useful for cooling the rearmost stages of an advanced turbine engine compressor where the temperature could be substantially high due to a very high-pressure ratio across the compressor.