Dimple Generators of Longitudinal Vortex Structures

Abstract To obtain a better insight into the unsteady flow behavior in side channel pumps by a robust vortex identification method, this study presents the efficacy of the new Ω-criterion in characterizing the evolution of vortex structures in the turbulent flows under different time steps. The flow behavior and the underlying vorticity dynamics were revealed as well. Compared to Q-criterion, the new Ω-criterion identified all vortex structures irrespective of the intensity at a universal threshold of 0.52. Three different types of vortex structures (longitudinal, axial, and radial) were identified to be responsible for the turbulent flows in the side channel pumps. The beneficial longitudinal vortex promotes the momentum exchange flow between the impeller and side channel which leads to the high hydraulic head of side channel pumps. On the other hand, the unfavorable axial and radial vortex structures restricted in the impeller passage mitigate the exchange process accounting for the low efficiency of the pumps. From this study, it can be established that the evolution of the axial vortex structures is responsible for the largest vortex distribution in the impeller compared to the total vortex evolved. The impeller outer radius contributes about 60% of the unfavorable axial structures evolved. Using the new Ω-criterion, many reported anomalous findings have been explained.

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Longitudinal vortex structures and heat transfer in the region of attachment of a supersonic turbulent boundary layer

Journal of Applied Mechanics and Technical Physics ◽

10.1007/bf00858036 ◽

1991 ◽

Vol 32 (2) ◽

pp. 204-210

Author(s):

E. G. Zaulichnyi ◽

V. M. Trofimov

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Turbulent Boundary Layer ◽

Vortex Structures ◽

Longitudinal Vortex

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SOME FEATURES OF A LAMINAR FLOW STABILITY LOSS IN A PIPE

Journal of Numerical and Applied Mathematics ◽

10.17721/2706-9699.2021.1.07 ◽

2021 ◽

pp. 59-65

Author(s):

G. A. Voropaiev ◽

O. O. Baskova

Keyword(s):

Reynolds Number ◽

Dynamic Viscosity ◽

Viscosity Coefficient ◽

Stability Loss ◽

Vortex Structures ◽

Longitudinal Vortex ◽

Necessary Condition ◽

Dimensional System ◽

Wall Region ◽

Variable Parameters

Despite the seeming simplicity of the steady flow in a pipe of constant radius, the question of the cause and process of the transition remains debatable. Especially since the necessary condition for the stability loss of parabolic profile is not satisfied, and the linear theory of hydrodynamic stability for an axisymmetric Poiseuille flow does not give growing axisymmetric eigen solutions for any Reynolds numbers, since the terms characterizing the interaction of disturbances with the initial velocity profile drop out in the linearized equations of momentum conservation. The report presents the results of the study of stages of convective stability loss for the flow at the initial section of the pipe depending on the variable parameters based on the numerical solution of the three-dimensional system of unsteady Navier-Stokes equations and the equation energy transfer. The variable parameters in this study were: Reynolds number, magnitude and gradient sign of the dynamic viscosity coefficient arising in nonisothermal flows. An analogy of the arising secondary axisymmetric large-scale toroidal vortex structures in the near-wall region to Tollmien-Schlichting waves in the region of the transition of the laminar boundary layer on the plate is shown. The subsequent loss of axisymmetry and stability of these torus-like vortex structures is analyzed, which leads to the formation of fairly regular longitudinal vortex structures downstream, the nonlinear interaction of which leads to chaotization of the flow. The lengths of these sections are determined depending on the Reynolds number, the magnitude and sign of the gradient of the dynamic viscosity coefficient.

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Investigation on the Flow Behavior of Side Channel Pumps Based on Vortex Identification

Chinese Journal of Mechanical Engineering ◽

10.1186/s10033-021-00649-1 ◽

2021 ◽

Vol 34 (1) ◽

Author(s):

Fan Zhang ◽

Desmond Appiah ◽

Ke Chen ◽

Shouqi Yuan ◽

Kofi Asamoah Adu-Poku ◽

...

Keyword(s):

Turbulent Flows ◽

Pressure Pulsation ◽

Flow Behavior ◽

Vortex Structures ◽

Longitudinal Vortex ◽

Navier Stokes ◽

Side Channel ◽

Vortex Identification ◽

Momentum Exchange ◽

Highly Turbulent Flows

AbstractThe momentum flow exchange between the impeller and side channel produces highly turbulent flows in side channel pumps. The turbulent flows feature complex patterns of vortex structures that are partly responsible for the dissipation of energy losses and unsteady pressure pulsations. The concept of turbulent flows in side channel pumps requires a reliable vortex identification criterion to capture and predict the effects of the vortex structures on the performance. For this reason, the current study presents the application of the new Ω-criterion to a side channel pump model in comparison with other traditional methods such as Q and λ2 criteria. The 3D flow fields of the pump were obtained through unsteady Reynolds-averaged Navier-Stokes (RANS) simulations. Comparative studies showed that the Ω-criterion identifies the vortex of different intensities with a standard threshold, Ω=0.52. The Q and λ2 criteria required different thresholds to capture vortex of different intensities thus leads to subjective errors. Comparing the Ω-criterion intensity on different planes with the entropy losses and pressure pulsation, the longitudinal vortex plays an important role in the momentum exchange development which increases the head performance of the pump. However, the rate of exchange is impeded by the axial and radial vortices restricted in the impeller. Therefore, the impeller generates the highest entropy loss and pressure pulsation intensities which lower the output efficiency. Finally, the findings provide a fundamental background to the morphology of the vortex structures in the turbulent flows which can be dependent upon for efficiency improvement of side channel pumps.

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