Response of a Disk Cavity Flow to Gas Turbine Engine Transients

An integral part of the transient operation of a gas turbine engine is the behavior of the engine’s internal air system. It is desirable to model transient air system effects using a computationally efficient method, while accurate representation of these flows may require incorporation of the interactive effects of volume packing and swirl. Thus 1-D methods may need auxiliary relations to account for non-uniformity of properties in the cavity due to swirl or changes in the discharge coefficients of feed and exit holes to account for varying amounts of cross-flow. Consideration of the system response shows that flow spin-up times can be significant, suggesting the inclusion of the conservation of angular momentum in a 1-D volume modeling approach. To clarify the various contributions to the dynamics of these cavities, an axisymmetric rotor-stator disk geometry was modeled using CFD. Results are presented showing a notable effect of rotation. The presence of the rotor increased the time constant by a factor of about 2 for one case studied. The CFD results are compared to 1-D models. The results show improved accuracy of the 1-D model when the conservation of angular momentum is included in the formulation and recommendations for further improvement are made.