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# Experimental investigation of the swirl development at the inlet of a coaxial rotating diffuser or nozzle

[+] Author and Article Information
Ferdinand-J. Cloos

Graduate Research Assistant, Chair of Fluid Systems, Department of Mechanical Engineering, Technische Universität Darmstadt, Darmstadt, Hesse, Germany 64287

Peter F. Pelz

1Corresponding author.

ASME doi:10.1115/1.4042095 History: Received February 06, 2018; Revised November 12, 2018

## Abstract

When a fluid enters a rotating pipe, a swirl boundary layer with thickness of $\tilde{\delta}_\mathrm{S}$ appears at the wall and interacts with the axial momentum boundary layer with thickness of $\tilde{\delta}$. The swirl is produced by the wall shear stress and \hlN{is not due to kinematic affects}. In the center of the pipe, the fluid is swirl-free and is accelerated due to axial boundary layer growth. Below a critical flow number $\varphi<\varphi_\mathrm{c}$, there is flow separation, known in the turbomachinery context as part load recirculation.

Previous work analyses the flow at the inlet of a coaxial rotating circular pipe ($\tilde{R}=\tilde{R}_0$). For a systematic approach to a turbomachine, the influence of the turbine's and pump's function on the evolution of the swirl and flow separation is to analyse. \hlN{The turbine's or pump's is schematically fulfilled by a diffuser or a nozzle, respectively.} The radius of the rotating pipe depends linearly on the axial coordinate, yielding a rotating circular diffuser or nozzle. The swirl evolution depends on the Reynolds number, flow number, axial coordinate and apex angle. The influence of the \hlN{apex angle is the main task by this investigation}. The circumferential velocity component is measured \hlN{via} 1D Laser Doppler Anemometry to investigate the swirl evolution.

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