School of Engineering, The University of Queensland
Abstract
Vortices can be produced and ingested in to the intake of a jet engine during its operation. This can occur when the plane is on the runway during take-off, or during engine tests in a test cell. The vortex can throw debris into the intake or stall the compressor, causing severe damage to the engine. The runway problem is solved by keeping the runway clear of debris and scheduling the throttle appropriately. However vortices can still occur in test cells. To eliminate vortices at the design stage it is necessary to be able to predict the onset of the vortex. This paper seeks to use the commercial CFD code Fluent to investigate both the runway and test cell problem. The runway problem has been investigated in previous wind tunnel studies by other authors. These studies were recreated in a CFD simulation reported in detail elsewhere. The threshold conditions for vortex formation were located and the effects of suction tube diameter, shear in the test cell inlet, ground boundary layer thickness and suction inlet Reynolds number were investigated. With the computational techniques thus validated, the study is extended to enclosed test cell geometries. The simulations show three stages of flow regime namely regular vortex, deformed vortex and no vortex. Vortices are not formed at cell bypass ratios greater than 50-70% and stable vortices are formed at cell bypass ratios less than 20-30%. The vortex threshold is found to be lower than the threshold for suction over ground plane simulations on the Vi/Vo against H/Di graph, i.e. vortex formation occurs over a wider range of conditions when the flow is enclosed
