Abstr:Axial compressor cascade
Application Area 6: Turbomachinery Internal Flows
Application Challenge AC6-10
Experimental investigations on the boundary layer and loss behaviour on a high turning compressor cascade up to 0.90 inlet Mach number were performed in the High Speed Cascade Wind Tunnel of DFVLR Braunschweig. The main objective of these investigations was to obtain accurate data for the validation of theoretical methods. The V2 cascade has a design point inlet Mach number of 0.85 and flow turning of 50o.
CFD results available include calculations using the STAR-CD commercial CFD code. The steady state compressible Navier-Stokes equations using a variant of the k-e model for closure were solved using the SIMPLE algorithm. Discretisation was undertaken using the second-order MARS scheme with the default compression level of 0.5. The computational domain covers one blade pitch with the blade located centrally in the domain and an axial extent of -0.8 to 1.8 axial chords from the leading edge.
The ECA2-V2 cascade was tested over a wide range of operating conditions, from high incidence/stall to choke flow and from low Mach number up to high subsonic flow. The transonic flow range and the high level of turning make it a challenging case, which is relevant to modern turbomachinery flows. Increased turning and higher blade loading are required as designers attempt to reduce the weight and size of gas turbine components whilst maintaining high pressure ratios. This application challenge is an ideal test case for assessing the ability of CFD codes to predict the detailed flow features and overall performance of a compressor blade row.
The design and assessment parameters can be grouped into firstly, overall performance indicators and secondly, parameters used to evaluate more detailed flow behaviour. The operating point of the cascade is defined by the inlet Mach number, inlet flow angle and Axial Velocity Density Ratio (W). The latter quantity defines the variation of streamtube thickness through the cascade in the axial direction. The ability to vary the streamtube thickness enables the endwall effects present in cascade testing to be controlled.
The overall performance parameters used for evaluation were exit Mach number, exit flow angle (hence flow turning) and pressure loss.
To evaluate blade surface pressure distributions a non-dimensional pressure coefficient was defined.
For more detailed evaluation of the pressure loss, profiles of pressure loss coefficient were plotted across the wake.
Boundary layer measurements were carried out at different positions on the blade suction side at the midspan position.
Contributors: Michael Dickens; Alex Read - Computational Dynamics Ltd