Abstract
The motivation for the current work is to improve the transient fluid analysis capability for turbomachinery fluid systems. An integral part of the transient operability of a gas turbine is the transient behavior of these fluid systems. Many aspects of these systems may be analysed using currently available methods in published literature and these are reviewed thoroughly herein. Complications in the analysis of air systems arise when the cavity flow being modelled contains a significant amount of rotation. In this case, where the vortex spin-up time and the resultant pressure gradient response cannot be neglected, no 1-D transient modelling methodology previously existed. A new 1-D formulation for computing the time varying properties of rotating flows in cavities with rotating or static walls is described. The model may be used in cases of inflow or outflow with varying amounts of inlet swirl. This methodology has been implemented using the Simulink simulation environment such that it can now be used for carrying out transient simulation under a range of applications. The accuracy of the underlying method and implementation is then demonstrated under a broad range of test cases. In one case, transient outflow in a rotor/stator disk cavity is examined using 2-D CFD and the 1-D model. For the particular disk cavity flow analysed with CFD, rotational effects almost doubled the pressure response time at the lower flow rate. It was shown here that the 1-D modeling method is a viable approach to this problem, capable of reproducing many of the effects observed in a CFD solution for a rotor-stator disk cavity with outflow. Another case presents deswirl nozzle fed, rotating cavities with radial inflow. A transient model of a compressor drum was able to reproduce the hysteresis, discontinuities and regions of no steady-state solution behavior observed in the experiments. In this case, a model with transient capability is required as a steady state model would choose one of the multiple solutions without physical justification. Recommendations are made that will eliminate this undesirable behavior on future rig tests. In the final case study, the 1-D model is incorporated in a network model for a three port vortex amplifier. A method has been devised for coupling the vortex cavity modelled Simulink with the balance of the system, modelled in AMESim. It is shown that the model is capable of predicting the relevant frequencies in the device response. It has therefore been demonstrated that the novel 1-D method proposed offers a practical, general predictive capability for transient air system network modeling.