15th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
Authors
Abstract
In the case of ducted axial flow fans tip leakage vortex forms due to the pressure difference at the blade tip. The vortex has a significant influence over the flow in the blade passage: based on the fan geometry and the operation point, the tip leakage vortex either leaves the blade passage or impinges on the pressure side of the following blade [1]. By impinging on the following blade, the tip leakage vortex causes a large amount of blockage in the blade passage as well as interacts with the tip leakage flow of said blade; therefore, substantial additional losses are generated. Thus, the vortex wandering of the tip leakage flow near the limit of impingement deserves attention. The tip leakage flow can cause up to nearly a third of the hydraulic losses of the fan and, in many cases, has been identified as the dominant sound source. Therefore, numerous studies are investigating the phenomenon, in many cases using numerical simulations as well. However, the most commonly used Reynolds-averaged simulations assume stationary flow and are thus unable to describe the transient behavior of the tip leakage vortex adequately. The flow visualization is challenging during the examination of the tip leakage vortex. In both measurement and numerical simulation results, the tip vortex is mainly represented by streamlines or a simple vortex identification method. However, these flow visualizations are not able to determine the core, i.e., the position of the vortex. Thus, these methods are sufficient for qualitative findings, but quantitative results cannot be filtered out. In contrast to flow visualization methods, vortex core detection methods are able to track the motion of the vortex core; thus, the change in the vortex location over time can also be quantified. In the case of strongly curved vortices, a higher-order vortex identification method is required, such as the method presented by Roth and Peikert [2] for the detection of the vortex line. Based on the above, in the present paper, the blade tip leakage flow of a low-speed axial flow fan will be investigated with an unsteady Reynolds-averaged Navier-Stokes simulation. Complementing this and supporting the processing of the results, a vortex core identification method will be implemented to localize the tip leakage vortex core and quantify the extent of the vortex wandering. [1] Benedek, T., Vad, J., Lendvai, B. (2022). Combined acoustic and aerodynamic investigation of the effect of inlet geometry on tip leakage flow noise of free-inlet free-exhaust low-speed axial flow fans. Applied Acoustics. 187. 108488. DOI: 10.1016/j.apacoust.2021.108488. [2] Roth, M. & Peikert, R. (1998). A higher-order method for finding vortex core lines. Proc. Visualization '98. 143-150. DOI: 10.1109/VISUAL.1998.745296.
ETC2023-231
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