Effect of inverse blade angle slots on a transonic rotor performance and stability

A subsonic axial rotor with axial skewed slot casing treatment (ASSCT) was investigated with experimental and numerical methods to explore the effects of the center offset degree (Cod) on the rotor...

Mechanism of affecting the axial rotor stability and performance with center offset degrees of axial skewed slots

This paper presents experimental results of a single stage transonic axial flow compressor coupled with low porosity bend skewed casing treatment. The casing treatment has a plenum chamber above the bend slots. The depth of the plenum chamber is varied to understand its impact on the performance of compressor stage. The performance of the compressor stage is evaluated for casing treatment and plenum chamber configurations at two axial locations of 20% and 40%. Experimental results reveal that the stall margin of the compressor stage increases with increase in the plenum chamber volume. Hot-wire measurements show significant reduction in the turbulence intensity with increase in the plenum chamber volume compared to that with the solid casing at the stall condition. At higher operating speeds of 80% and at 20% axial coverage, the stall margin of the compressor increases by 20% with half and full plenum depth. The improvement in the peak stage efficiency observed is 4.6% with half plenum configuration and 3.34% with the full plenum configuration. The maximum improvement in the stall margin of 29.16% is obtained at 50% operating speed with full plenum configurations at 40% axial coverage.

https://downloads.hindawi.com/journals/ijrm/2014/625876.pdf

Improvement of Moderately Loaded Transonic Axial Compressor Performance Using Low Porosity Bend Skewed Casing Treatment

This paper seeks to reveal the mechanisms of enhancing the stability of a subsonic axial flow rotor by applying blade angle slots casing treatment (BSCT). When blade angle slots are applied, there ...

Mechanism investigation of enhancing the stability of an axial flow rotor by blade angle slots

This contribution describes the experimental investigation of the blade tip interaction with a casing treatment implemented to a transonic compressor stage using particle image velocimetry (PIV). The results obtained allowed for direct comparison with numerical simulations of the same compressor stage including the CT geometry, carried out using the DLR TRACE code following a new approach to efficiently perform time-accurate casing-treatment simulations.
The single-stage transonic axial compressor was equipped with a casing treatment (CT), consisting of 3.5 axial slots per rotor pitch in order to investigate the predicted extension of the stall margin characteristics. Contrary to most other studies, the CT was designed especially accounting for an optimized optical access in the immediate vicinity of the CT, rather than giving maximum benefit in terms of stall margin extension. The nearly rectangular geometry of the CT cavities allowed one dividing bridge between two slots to be made of quartz glass with curvatures matching the casing. Thus the flow phenomena could be observed with essentially no disturbance caused by the optical access. Two periscope light sheet probes were specifically designed for this application to allow for precise alignment of the laser light sheet at three different radial positions in the rotor tip region (at 87.5%, 95% and 99% blade height). For the outermost radial position the light sheet probe was placed behind the rotor and aligned to pass the light sheet through the blade tip clearance. It was demonstrated that the PIV technique is capable of providing velocity information of high quality even in the tip clearance region of the rotor blades. Phase-constant measurements were carried out with a resolution of 8 phase angles per blade pitch in relation to the CT slots visible in the camera’s field of view. The chosen type of smoke-based seeding with very small particles (about 0.5 µm in diameter) supported data evaluation with high spatial resolution, resulting in a final grid size of 0.5 x 0.5 mm.
The PIV data base established in this project forms the basis for further detailed evaluations of the flow phenomena present in the transonic compressor stage with CT and allows validation of accompanying CFD calculations using the DLR TRACE code. Based on the combined results of PIV measurements and CFD calculations of the same compressor and CT geometry a better understanding of the complex flow characteristics can be achieved.

PIV Application for Investigation of the Rotor Blade Tip Interaction with a Casing Treatment in a Transonic Compressor Stage

A casing treatment with axial and radial skewed slots ending in a plenum chamber has numerically been investigated at a highly subsonic axial compressor stage. The aim was to understand the physical phenomena of this treatment family that are responsible for the stabilization of the blade passage flow and the drop in efficiency mostly observed. Unsteady 3D Reynolds-averaged simulations were performed with the commercial CFD Code TASCflow 2.12. The closure problem was faced with a standard k-e high Reynolds turbulence model and a logarithmic wall function. Two configurations with solid casing and casing treatment were investigated at the operating points with maximum efficiency and on the stability line. The experimentally gained performance results of this configuration show an extension of the operating range of approximately 50% based on the operating range at nominal speed, while the efficiency for design conditions falls by 1.4%. Apart from this, measurements at part load conditions show operating points without any loss in efficiency. The numerical simulations predict this efficiency drop as well. The detailed analysis is performed for the solid casing and casing treatment configuration at the operating point on the stability line. Influences of the incidence flow, the tip clearance vortex and the blade suction side separation were investigated. Special interest is directed towards the interaction of the casing treatment with the blade passage flow field and a detailed analysis of the flow inside the casing treatment, the effect of the plenum chamber and the interaction with the treatment slot flow is performed.© 2007 ASME

R. Kunte

Papers

Time Resolved Investigations of an Axial Compressor With Casing Treatment: Part 2 — Simulation