Numerical studies of laminar flow in ducts and pipes

When a fluid enters a rotating circular pipe a swirl boundary layer with thickness ofδ S appears at the wall and interacts with the axial momentum boundary layer with thickness ofδ. We investigate the turbulent flow applying Laser-Doppler-Anemometry to measure the circumferential velocity profile at the inlet of a rotating pipe. The measured swirl boundary layer thickness follows a power law taking Reynolds number and flow number into account. A critical combination of Reynolds number, flow number and axial position causes a transition of the swirl boundary layer development in the turbulent regime. At this critical combination, the swirl boundary layer thickness as well as the turbulence intensity increase and the latter yields a self-similarity. The circumferential velocity profile changes to a new presented self-similarity. A method is established to define the transition inlet length, when the transition appears and a stability map for two regimes is given.

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“…For small Reynolds numbers, e.g. laminar flow, flow separation is investigated by Lavan and others in a rotating pipe [20][21][22].…”

Section: Literature Reviewmentioning

confidence: 99%

Two turbulent flow regimes at the inlet of a rotating pipe

Cloos

Zimmermann

Pelz

2017

European Journal of Mechanics - B/Fluids

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“…The separation is caused by the sudden pressure increase due to swirl at the wall. At the inlet of a rotating pipe, the flow separation is analytically and numerically investigated by a laminar flow with Re < 10 3 (Lavan, Nielsen & Fejer 1969;Crane & Burley 1976). For small Reynolds numbers Re 10 3 , the critical flow number is a linear function of the Reynolds number (Lavan et al 1969;Crane & Burley 1976), but for Re > 10 2 , the linear relation loses its validity (Crane & Burley 1976).…”

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confidence: 99%

Swirl boundary layer and flow separation at the inlet of a rotating pipe

2016

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When a fluid enters a rotating circular pipe, an angular momentum or swirl boundary layer appears at the wall and interacts with the axial momentum boundary layer. In the centre of the pipe, the fluid is free of swirl and is accelerated due to boundary layer growth. Below a critical flow number, defined as the ratio of average axial velocity to circumferential velocity of the pipe, there is flow separation, known in the turbomachinery context as part load recirculation. To describe this phenomenon analytically, we extended boundary layer theory to a swirl boundary layer interacting with the axial momentum boundary layer. The solution of the resulting generalized von Kármán momentum equation takes into account the influence of the Reynolds number and flow number. We show the impact of swirl on the axial boundary layer and conduct experiments in which we vary Reynolds number, flow number and surface roughness to validate the analytical results. The extended boundary layer theory predicts a critical flow number which is analytically derived and validated. Below this critical flow number, separation is expected.

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“…The flow separation in the generic model for laminar flow with small Reynolds number is analytically, experimentally and numerically well investigated. For the laminar case, the critical flow number increases with increasing Reynolds number [1], [2], [3], [4], [5]. In the pre-studies of this work [6] it was shown by experimental and numerical studies that for turbulent flow the critical flow number decreases again with .…”

Section: Review On Previos Workmentioning

confidence: 61%

Evolution of Swirl Boundary Layer and Wall Stall at Part Load: A Generic Experiment

Stapp

Pelz

2014

Volume 2A: Turbomachinery

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The influence of Reynolds number, roughness and turbulence on the onset of wall stall is up to now not sufficiently understood. To shed some light onto the interdependency of near wall flow with growing swirl component, the simplest “machine” is tested. The apparatus we examine is a circular pipe at rest followed by a rotating co-axial pipe segment. In the sense of a generic experiment this machine represents a very basic model of the inlet of an axial machine. Due to the wall shear stress a swirl boundary layer is formed in the rotating pipe segment, interacting with the axial boundary layer. The evolution of the swirl velocity profile with increasing axial distance from the rotating pipe inlet is measured for various Reynolds numbers, flow numbers and degrees of turbulence by means of Laser Doppler Anemometry. We observe a self-similarity in the swirl velocity profile, for subcritical flow number and develop a scaling law for the velocity distribution in the transition section of a rotating pipe. At critical flow number the boundary layer is separating, resulting in a ring vortex at the inlet of the rotating pipe. Our work fills the gap of previous experimental works, with respect to high Reynolds numbers and low flow numbers. The parameter field we examine is most relevant for turbomachinery application and wall stall. In addition our boundary layer resolution is sufficient to resolve the swirl boundary layer thickness. Only this high resolution enables us to generalize the experimental findings by means of a similarity distribution of the velocity profile within the swirl boundary layer.

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Numerical studies of laminar flow in ducts and pipes

Cited by 21 publications

References 19 publications

Two turbulent flow regimes at the inlet of a rotating pipe

Two turbulent flow regimes at the inlet of a rotating pipe

Swirl boundary layer and flow separation at the inlet of a rotating pipe

Evolution of Swirl Boundary Layer and Wall Stall at Part Load: A Generic Experiment

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