Experimental and Numerical Analysis of a Compressor Stage under Flow Distortion

Abstract

On many occasions, fan or compressor stages have to face azimuthal flow distortion at inlet, which affects their performance and stability. These flow distortions can be caused by external events or by some particular geometrical features. The aim of this work is to propose a joined numerical and experimental analysis of the flow behavior in a single axial compressor stage under flow distortion. The distortions are generated by different grids that are placed upstream to the rotor. Experimentally, the flow analysis is based on the measurements obtained by a series of unsteady pressure sensors flush-mounted at the casing of the machine rotor. URANS computations are conducted using the elsA software. The flow distortion is simulated by a drop of stagnation pressure ratio at the inlet boundary condition. The study is focusing first on the ability of a pressure drop, imposed as an inlet boundary condition in CFD, to reproduce accurately the effect of a flow distortion. The analysis is conducted using singular value decomposition (SVD) and dynamic mode decomposition (DMD). A special attention is then paid, on the experimental level, to the arising of rotating stall, from the onset of the instability up to completely developed stall cells.

Numerical Investigations on the Rotating Stall in an Axial Compressor and Its Control by Flow Injection at Casing

“…Since the flow is no more periodic in space and in time, it is necessary to use a full annulus grid, obtained by duplicating ten times the previous mesh in order to reach a 360° sector, leading to a grid composed of almost 500 blocks and 150 million cells. The non dimensionalised wall cell (y+) is less than 1, and a grid sensitivity analysis had been previously performed [26] on this compressor case, showing that grid independency is obtained and that the current grid is acceptable.…”

“…For the URANS computations, the physical time step has a value close to 1s corresponding to 18,000 time steps to perform a single rotation. Previous study [26] showed that the chosen time step values enables a satisfactory capture of the main unsteady phenomenon, in particular the rotating stall phenomena The one equation Spalart-Allmaras model [25] is used for turbulence, previous studies having shown its ability to capture rotating stall phenomenon [27]. Concerning the boundary conditions, their locations are depicted in Figure 7, especially inlet/outlet planes and mixing planes.…”

Effect of Tip Gap Size on the Performance of an Axial Compressor Stage with and without Active Flow Control

“…This code relies on a cell-centered finite-volume discretization on structured and unstructured multi block meshes. A convergence study based on two types of mesh for a single-blade channel configuration without injectors, one at 10 6 and the other at 3 × 10 6 nodes was performed in [14]. The last mesh was selected as it presented a good compromise between numerical cost and reliability.…”

Effect of the Axial Compressor Tip Clearance Size: Performance and Transition to Rotating Stall

“…This code relies on a cellcentered finite-volume discretization on structured multi block meshes. A convergence study has been conducted with 10 6 and 2.10 6 nodes in order to study the compromise between computational cost and reliability in previous papers as quoted in [14]. Reynolds-Averaged Navier-Stokes equations are solved for compressible flows.…”