Unsteady Flow Structure in an Axial Compressor at Windmill Condition

Abstract

This study investigates experimentally and numerically unsteady flow fields in an axial compressor operating at high-flow rate in order to understand the flow structure in the stator row operating at windmill condition. The experimental and numerical data are compared by time- and phase-lock-averaged techniques. Additionally, unsteady vortex structure is investigated by numerical technique. At windmill condition, the incidence angle to the stator row becomes extremely negative. Therefore, large separation occurs near pressure surface in the stator passage. The experimental and numerical results indicate that a large vortex is generated in the separation area. According to the numerical results, part of the vortex migrates downstream, and the vortex produces blockage of the main stream of the stator passage. Therefore, net flow area in the stator passage becomes small so that the flow between the vortex and suction side of stator vane is accelerated. As a result, the total pressure deterioration is generated in the stator passage because the high speed flow and the vortex cause high shear.

Evolution Process of Diffuser Stall in a Centrifugal Compressor With Vaned Diffuser

“…The present simulations were conducted using an in-house computational fluid dynamics (CFD) code, which had been validated for various turbomachinery flows [12,18,19] [20], which was extended to the third order using the monotonic upwind scheme for conservative laws (MUSCL) interpolation [21]. The viscous flux was determined as a second-order central difference by using Gauss's theorem.…”

Assessment of Steady and Unsteady Full Annulus Simulations Predictivity for a Low-Speed Axial Fan at Load-Controlled Windmill

“…Regarding the predictivity, on turbofans at freewindmill, it is generally reported that numerical radial distributions at rotor outlet are in good agreement with experimental data, which is not the case at stator outlet (steady mixing plane simulation [5] and unsteady simulation on 1/12 and 1/10 sector of the full annulus [6,7]). This comes from the fact that losses mechanisms are not well captured.…”

“…To check this assumption, the unsteady calculation presented here was carried out. Regarding the unsteadiness of windmilling flows, a 2D NLH approach [9] from Dufour et al [5,10] and an unsteady calculation on 1/12 sector of full annulus from Goto et al [6] underline the existence of a vortex-shedding phenomenon occurring in the stator. According to Dufour, the rotor wakes that periodically impact the stator blades are responsible for a continuous modification of the stator angle of attack which leads to a more or less intense separation.…”

“…According to Dufour, the rotor wakes that periodically impact the stator blades are responsible for a continuous modification of the stator angle of attack which leads to a more or less intense separation. Goto et al [6] try to analyze this vortex-shedding on a 3D point of view but because of the complexity of the pattern more investigation is needed. One of the objectives in this paper is to analyze the temporal evolution of the 3D stator separation, in particular by taking into account its radial unsteady behaviour.…”

Generic Properties of Flows in Low-Speed Axial Fans Operating at Load-Controlled Windmill

“…Regarding load-controlled windmill, little information was available in the literature until the last 3 years, from which dedicated contributions began to appear [7][8][9][10][11]. From the time being, no work enabled to underline some unexpected behaviors typical of this severe far off-design regime; it is the objective of the present work.…”