Computational Study of the Heat Transfer of the Buoyancy-Driven Rotating Cavity With Axial Throughflow of Cooling Air

Abstract

Buoyancy driven flows that occur in the inter-disk space of an axial compressor spool play a major role in projecting gas turbine engine life and performance. The Rayleigh-Benard-like flow structure developed under the influence of centrifugal buoyancy creates sharp temperature gradients at the rotating walls of the compressor hardware. These sharp temperature gradients greatly influence the running stresses inside the machine and therefore affecting its life. The objective of this work is to generate a complete set of computationally-derived Nusselt number correlations that will be used in conducting the conjugate heat transfer analyses. The impact of engine power condition (Idle, Highpower, and Shutdown) on the heat transfer of these rotating cavities is studied under the wide range of operating conditions encountered by realistic turbomachines. A computational analysis is performed using commercially available computational tools for grid generation (ICEM-CFD) and turbulent-flow simulation (CFX). A total of fifty steady CFD cases for two different cavity configurations were analyzed. The CFD computed results of these cases were used to generate a complete set of Nusselt number correlations for different cavity geometry (gap ratios), flow regimes (forced and free convection dominated regimes), and operating conditions (Rossby Number Ro, Rotational Rayleigh Number RaΩ, and axial Reynolds Number Rez). The CFD computed heat-transfer results revealed that, despite the complicated flow patterns inside these cavities, and despite the large variation in their geometry, the simple Nusselt number correlations for free convection from a vertical flat plate with constant temperature can be used to predict the global Nusselt number values for the buoyancy-dominated regime of all such cavities. Furthermore, the Nusselt number correlations for the laminar and turbulent forced convection over a flat plate can be used to predict the global Nusselt number values for the central-jet dominated regime.

Experimental and Computational Investigation of Flow Structure of Buoyancy Induced Flow in Heated Rotating Cavities

“…The results from the test cases showed a consistent agreement with the data from Johnson et al (Johnson, et al, 2006). The above authors also showed that despite the unstable and evolutionary nature of the complicated flow pattern, the free convection correlations for a vertical flat plate with constant temperature gives an encouraging prediction for the global Nusselt number values for the buoyancy-induced flow (Dweik, et al, 2009a). Atkins and Kanjirakkad (Atkins & Kanjirakkad, 2014) conducted measurements in the same multiple cavity rig as (Alexiou, 2000;Long, et al, 2007) but this time with a stationary shaft and the direction of flow through the rig reversed compared to the previous builds.…”

Experimental and computational investigation of flow structure of buoyancy induced flow in heated rotating cavities

“…The results from the test cases showed a consistent agreement with the data from Johnson et al (2006). The above authors also showed that despite the unstable and evolutionary nature of the complicated flow pattern, the free convection correlations for a vertical flat plate with constant temperature gives an encouraging prediction for the global Nusselt number values for the buoyancy-induced flow (Dweik et al, 2009a). Atkins and Kanjirakkad (2014) conducted measurements in the same multiple cavity rig as (Alexiou, 2000;Long et al, 2007) but this time with a stationary shaft and the direction of flow through the rig reversed compared to the previous builds.…”

Some Observations on the Computational Sensitivity of Rotating Cavity Flows

“…All of these are relevant for rotating cavity flows. It is therefore confusing that many simulations that have been conducted with URANS [10,[23][24][25][26] have provided reasonable predictions of the disk heat flux.…”