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A compressible flow code that can predict the nonlinear unsteady aerodynamics associated with transonic flows over oscillating cascades is developed and validated. The code solves the two-dimensional, unsteady Euler equations using a time-marching, flux-difference splitting scheme. The unsteady pressures and forces can be determined for arbitrary input motions, although this paper will only address harmonic pitching and plunging motions. The code solves the flow equations on a H-grid which is allowed to deform with the airfoil motion. Predictions are presented for both flat plate cascades and loaded airfoil cascades. Results are compared to flat plate theory and experimental data. Predictions are also presented for several oscillating cascades with strong normal shocks where the pitching amplitudes, cascade geometry and interblade phase angles are varied to investigate nonlinear behavior.

Buoyancy driven flows such as the one that occurs in the inter-disk space of an axial compressor spool plays a major role in determining the gas turbine engine projected life and performance. Details of the developed flow structure inside these spaces largely impact the operating temperatures on the rotating walls of the compressor hardware and therefore impact the life of the machine. In this paper the impact of engine power condition (Idle, Highpower, and Shutdown) on the flow structure for these rotating cavities is studied under a 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 computational test case was developed to imitate the rig-test conditions of Owen and Powell, and computed results were assessed and validated by comparison with their experimental results. A total of fifteen unsteady CFD cases covering a wide range of operating conditions (Rossby Number Ro, Rotational Rayleigh Number Raφ, and axial Reynolds Number Rez) were analyzed. The computed flow results revealed that the flow structure evolution, starting from a steady state solution, is such that radial arms of different number (according to the engine power condition), surrounded by a co-rotating (cyclonic) and counter-rotating (anti-cyclonic) pair of vortices, start to form at different locations. Cold air from the central jet enters the cavity in these arms under the combined action of the centrifugal buoyancy and the Coriolis forces. As time proceeds, the flow structure tends to become virtually invariant with time in a repeatable pattern. The number of radial arms, strength of recirculation zones, and the degree of invasion of the central cooling air toward the shroud are all dependent on the engine power condition. The computations also revealed that at high rotational speed the flow stabilizes, and the unsteady features of the flow structure (cyclonic and anti-cyclonic recirculation zones surrounding the radial arms, radial invasion of the cooling air in the radial arms, and its final impingement upon the shroud surface) eventually disappear after a threshold value of the rotational speed is reached.

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.