Combining High Fidelity Simulations and Experiments to Optimize the Tip Flow and Casing Treatment in Advanced
Abstract
Modern fighter aircraft engines require large stability margins to accommodate deteriorated engine performance at off-design conditions. The stability of compressors in advanced engines is controlled by the flow in the rotor tip clearance region, where interactions of the leakage flow and tip leakage vortex (TLV) with the passage flow cause blockage, instabilities, rotating stall andsurge. Several casing treatment concepts have been used successfully to increase the stability margins, but they invariably result in an efficiency penalty at design conditions. Circumferentially discreet slots and circumferentially continuous grooves have been the most popular. The slots typically achieve greater improvements in stall margin than groove-types, but also cause larger efficiency penalties. In spite of numerous studies, the physical mechanisms affecting the onset of stall, its suppression by the casing treatment, and the reasons for the performance degradation at design flow rates are only partially understood and subject to disagreements. This collaboration between United Technologies Research Center (UTRC) and Johns Hopkins University (JHU) combines numerical simulations, experiments, and analysis to address this challenge. The objective of this program is to develop a process that allows design, testing, optimization, and implementation of casing treatment in advanced aircraft gas turbine compressors to improve theirstability without incurring an efficiency penalty. Characterization of machine performance as well as detailed stereo- and tomographic-Particle Image Velocimetry (PIV) measurements will be performed in the unique refractive index-matched liquid facility at JHU, using transparent compressor models. They fully resolve the unsteady 3D velocity and vorticity distributions over the entire rotor and stator passages. To support validations, the available data, which presently focuses on the tip region, will be extended to the entire rotor and stator passages. The pressure distributions and blade loading will also be mapped by spatiallyintegrating the measured Lagrangian acceleration using recently introduced methods. Ensemble averaging will provide the mean flow and distributions of turbulence parameters including all the Reynolds stress components. Initially, data obtained for the existing setup, with and without casing treatment, will be used to validate, assess, and, if needed, modify the turbulence models used inthe high-fidelity Unsteady Reynolds-Averaged Navier Stokes (URANS) codes available at UTRC. These validations will be performed at varying levels of detail, starting with overall performance, but then extending to predictions of the flow in the tip region, the instabilities leading to the onset of stall, and the interaction between the casing treatment and the tip-clearance flow. Specific causes for discrepancies will be investigated, and modeling approaches implemented for addressing them.This phase is aimed at producing reliable tools for predicting the flow structure and the impact of casing treatments. Subsequently, the validated UTRC codes will be applied to design, pre-screen, and optimize the blade load distributions and casing treatments, emphasizing geometries and approaches relevant to advanced military compressors. The optimized designs will maximize the stall margin improvement while minimizing the efficiency penalty at the design point. A transparent modelbased on this systematic analysis, with and without several casing treatments, will be constructed and studied experimentally as well. Analysis of the computational and experimental data along with integration of the substantial body of historical data and in-house experience will produce learning that will inform a robust process that would reduce the number of design iterations Johns Hopkins University United Technologies Research Center Proprietary Information. Use or disclosure of data contained on this sheet is subject to the restriction on the t
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 10, 2018
- Source ID
- N000141812430
Entities
People
- Joseph Katz
Organizations
- Johns Hopkins University
- Office of Naval Research
- United States Navy