Dynamic Characterization of Vortex Structures and Their Evolution Mechanisms in a Side Channel Pump

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Fan Zhang ◽  
Desmond Appiah ◽  
Ke Chen ◽  
Shouqi Yuan ◽  
Kofi Asamoah Adu-Poku ◽  
...  
Keyword(s):  
Turbulent Flows ◽  
Flow Behavior ◽  
Exchange Process ◽  
Vortex Structures ◽  
Longitudinal Vortex ◽  
Side Channel ◽  
Exchange Flow ◽  
Vortex Identification ◽  
Momentum Exchange ◽  
Low Efficiency

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.

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

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.

Vortex Identification in Turbulent Flows: Isotropic, Sphere Wake

2003 ◽  
Author(s):  
P. Chakraborty ◽  
S. Balachandar ◽  
R. J. Adrian
Keyword(s):  
Turbulent Flows ◽  
Spatial Coherence ◽  
Strength Criterion ◽  
Vortex Structures ◽  
Coherent Motion ◽  
Vortex Identification ◽  
Coherence Measure ◽  
Identification Schemes ◽  
Swirling Strength ◽  
Coherent Vortex

Vortices, the regions of swirling coherent motion of fluid, are of fundamental importance in understanding the dynamics of turbulent flows. Recent advances in computational and experimental resources have resulted in massive volumes of highly resolved flow field data. Identification of coherent vortex structures from these space-time discretized flow dataset is the key issue of vortex identification. We consider identification schemes based on pointwise analysis of the velocity gradient tensor. A new measure of the local spatial coherence in a vortex is introduced. Different criteria are compared for two classes of turbulent flows: isotropic and sphere wake. Remarkably similar vortex structures are observed using the Q, λ2 and swirling strength criterion. An explanation based on swirling strength and the proposed local coherence measure is offered for this observation.

A Three-Equation Eddy-Viscosity Model for Reynolds-Averaged Navier–Stokes Simulations of Transitional Flow

2008 ◽  
Vol 130 (12) ◽  
Author(s):  
D. Keith Walters ◽  
Davor Cokljat
Keyword(s):  
Boundary Layer ◽  
Turbulent Flows ◽  
Eddy Viscosity ◽  
Flow Behavior ◽  
Applied Pressure ◽  
Plate Boundary ◽  
Low Frequency ◽  
Transitional Flow ◽  
Test Cases ◽  
Eddy Viscosity Model

An eddy-viscosity turbulence model employing three additional transport equations is presented and applied to a number of transitional flow test cases. The model is based on the k-ω framework and represents a substantial refinement to a transition-sensitive model that has been previously documented in the open literature. The third transport equation is included to predict the magnitude of low-frequency velocity fluctuations in the pretransitional boundary layer that have been identified as the precursors to transition. The closure of model terms is based on a phenomenological (i.e., physics-based) rather than a purely empirical approach and the rationale for the forms of these terms is discussed. The model has been implemented into a commercial computational fluid dynamics code and applied to a number of relevant test cases, including flat plate boundary layers with and without applied pressure gradients, as well as a variety of airfoil test cases with different geometries, Reynolds numbers, freestream turbulence conditions, and angles of attack. The test cases demonstrate the ability of the model to successfully reproduce transitional flow behavior with a reasonable degree of accuracy, particularly in comparison with commonly used models that exhibit no capability of predicting laminar-to-turbulent boundary layer development. While it is impossible to resolve all of the complex features of transitional and turbulent flows with a relatively simple Reynolds-averaged modeling approach, the results shown here demonstrate that the new model can provide a useful and practical tool for engineers addressing the simulation and prediction of transitional flow behavior in fluid systems.

Study on Laminar Turbulent Transition in Square Arrayed Rod Bundles

2021 ◽  
Author(s):  
Carolina S. B. Dutra ◽  
Elia Merzari
Keyword(s):  
Turbulent Flows ◽  
Flow Behavior ◽  
Spectral Element ◽  
Linear Instability ◽  
Rod Bundles ◽  
Rod Bundle ◽  
Turbulent Transition ◽  
Spatio Temporal ◽  
The Stability ◽  
Laminar Turbulent Transition

Abstract The study of coolant flow behavior in rod bundles is of relevance to the design of nuclear reactors. Although laminar and turbulent flows have been researched extensively, there are still gaps in understanding the process of laminar-turbulent transition. Such a process may involve the formation of a gap vortex street as the consequence of a related linear instability. In the present work, a parametric study was performed to analyze the spatially developing turbulence in a simplified geometry setting. The geometry includes two square arrayed rod bundle subchannels with periodic boundary conditions in the cross-section. The pitch-to-diameter ratios range from 1.05 to 1.20, and the length of the domain was selected to be 100 diameters. No-slip condition at the wall, and inlet-outlet configuration were employed. Then, to investigate the stability of the flow, the Reynolds number was varied from 250 to 3000. The simulations were carried out using the spectral-element code Nek5000, with a Direct Numerical Simulation (DNS) approach. Data were analyzed to examine this Spatio-temporal developing instability. In particular, we evaluate the location of onset and spatial growth of the instability.

Investigation of the Matching Relation Between Impeller and Flow Channel of Regenerative Flow Pumps

2021 ◽  
Author(s):  
Qianqian Li ◽  
Chengshuo Wu ◽  
Bo Qian ◽  
Peng Wu ◽  
Bin Huang ◽  
...  
Keyword(s):  
Performance Optimization ◽  
Cfd Simulation ◽  
Flow Channel ◽  
Longitudinal Vortex ◽  
Exchange Flow ◽  
Low Velocity ◽  
Matching Mechanism ◽  
Regenerative Flow ◽  
Flow Pump ◽  
Matching Relation

Abstract As a specific radial flow pump, the regenerative flow pump (RFP) usually has a low efficiency. In this study, in order to explore the matching mechanism, three cases with various matching relations were investigated by the methods of theoretical calculation, computational fluids dynamics (CFD) simulation, and experiment test. The results illustrate that the theoretical prediction, numerical simulation and experimental data are in good agreement. Furthermore, when the matching relation expressed by a ratio of the channel's and blade's radial length is equal to 1, the geometrical profiles of RFP can well guide the circulation flow into the channel at large radii and into the impeller at small radii, forming intense longitudinal vortex. The steady, strong exchange flow is characterized by the inflow and outflow regions approximately half of the iso-surface. The axial vortex motion without apparent flow separation and irregular flow is observed in the impeller, a low velocity annulus exists in the medium radii of the impeller without other distinct velocity clouds, and a low velocity strip and a high velocity annulus in the channel are respectively performed along the blade's pressure surface and the channel's outer radii. All of this corresponds to the best pump's performance and the largest efficiency of the impeller and channel. This work promotes a systematical understanding of the matching mechanism between impeller and flow channel in the RFP and could provide some reference for the design and performance optimization for RFP.

Fluid Flow and Heat Transfer Behavior for Turbulent Flows in a Tube With Vortex Generator Pairs for an Efficient Heat Exchanger

2018 ◽  
Author(s):  
Md. Islam ◽  
Z. Chong ◽  
S. Bojanampati
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Turbulent Flows ◽  
Flow Behavior ◽  
Vortex Generator ◽  
Tube Diameter ◽  
Vortex Generators ◽  
Blockage Ratio ◽  
Delta Winglet

Various technologies have been developed to enhance flow mixing and heat transfer in order to develop an efficient compact heat exchanging devices. Vortex generators/turbulent promoters generate the vortices which reduce the boundary layer thickness and introduce the better mixing of the fluid to enhance the heat transfer. In this research experimental investigations have been carried out to study the effect of delta winglet vortex generator pairs on heat transfer and flow behavior. To generate longitudinal vortex flow, two pairs of the delta winglet vortex generators (DWVG) with the length of 10mm and winglet-pitch to tube-diameter ratio (PR = 4.8) are mounted on the inner wall of a circular tube. The DWVG pairs with two different winglet-height to tube-diameter ratios (Blockage ratio, BR = 0.1 and 0.2), three attack angles (α = 10°, 20°, 30°) and three spacings between leading edges (S = 10, 15 and 20mm) are studied. The experiments were conducted with DWVGs pairs for the air flow range of Reynolds numbers 5000–25000. The influence of the DWVGs on heat transfer and pressure drop was investigated in terms of the Nusselt number and friction factor. The experimental results indicate that DWVG pair in a tube results in a considerable enhancement in Nusselt number (Nu) with some pressure penalty. It is found that DWVG increases Nu up to 85% over the smooth tube. It is also observed that Nusselt number increases with Re, blockage ratio and attack angle. Friction factor decreases with Re but increases with blockage ratio, spacing and attack angle. And 30° DWVG pair with S = 20mm, BR = 0.2 gets the highest friction factor. The Highest thermal performance enhancement (TPE) was noticed for α = 10°, S = 20mm, BR = 0.2 for turbulent flows. To obtain qualitative information on the flow behavior and vortex structures, flow was visualized by laser sheet using smoke as a tracer supplied at the entrance of the test section. The generation and development of longitudinal vortices influenced by DWVG pairs were clearly observed.

Airside Velocity Measurement Above the Wind-Generated Water Waves

2007 ◽  
Author(s):  
Nasiruddin Shaikh ◽  
Kamran Siddiqui
Keyword(s):  
Water Waves ◽  
Flow Behavior ◽  
Momentum Exchange ◽  
Mean Velocity ◽  
Wind Speeds ◽  
Velocity Magnitude ◽  
Image Velocimetry ◽  
Sweeping Processes ◽  
High Level ◽  
The Waves

An experimental study conducted to investigate the airside flow behavior within the crest-trough region over wind generated water waves is reported. Two-dimensional velocity field in a plane perpendicular to the surface was measured using particle image velocimetry (PIV) at wind speeds ranging from 1.5 m s−1 to 4.4 m s−1. The results show a reduction in the mean velocity magnitude when gravity waves appear on the surface. A sequence of consecutive velocity fields has shown the bursting and sweeping processes and the flow separation above the waves. The results also indicate that the flow dynamics in the crest-trough region are significantly different than that at greater heights. High level of turbulence was observed in this region which could not be predicted from the measurements at greater heights. Thus, it is concluded that the quantitative investigation of the flow in the immediate vicinity of the interface is vital for an improved understanding of the heat, mass and momentum exchange between air and water.

Cycle Optimization Potential of Composite Cycle and Turbocompound Aero-Engines

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Felix Klein ◽  
Stephan Staudacher
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Pressure Ratio ◽  
Exchange Process ◽  
Aircraft Engine ◽  
Time Frame ◽  
Fuel Burn ◽  
Component Efficiency ◽  
Low Efficiency ◽  
Aero Engines

Abstract Fair comparison of future aircraft engine concepts requires the assumption of similar technological risk and a transparent book keeping of losses. A 1000 km and a 7000 km flight mission of a single-aisle airplane similar to the Aribus A321neo LR have been used to compare composite cycle engines, turbocompound engines and advanced gas turbines as potential options for an entry-into-service time frame of 2050+. A 2035 technology gas turbine serves as reference. The cycle optimization has been carried out with a peak pressure ratio of 250 and a maximum cycle temperature of 2200 K at cruise as boundary conditions. With the associated heat loss and the low efficiency of the gas exchange process limiting piston component efficiency, the cycle optimization filtered out composite cycle concepts. Taking mission fuel burn (MFB) as the most relevant criterion, the highest MFB reduction of 13.7% compared to the 2035 reference gas turbine is demonstrated for an air-cooled turbocompound concept with additional combustion chamber. An intercooled, hectopressure gas turbine with pressure gain combustion achieves 20.6% reduction in MFB relative to the 2035 reference gas turbine.

Investigation on the Energy Exchange Characteristics of the Regenerative Flow Pump in an Automobile Fuel System

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Qian-qian Li ◽  
Guo-shou Zhao ◽  
Cheng-shuo Wu ◽  
Peng Wu ◽  
Da-zhuan Wu ◽  
...  
Keyword(s):  
Energy Exchange ◽  
Cfd Simulation ◽  
Longitudinal Vortex ◽  
Axial Distance ◽  
Exchange Flow ◽  
Circulation Flow ◽  
Computational Fluids Dynamics ◽  
And Performance ◽  
Regenerative Flow ◽  
Flow Pump

Abstract The flow inside the regenerative flow pump (RFP) is quite complex. This study investigated four pump models with various geometrical dimensions to explore the energy exchange characteristics. A computational fluids dynamics (CFD) simulation and the experiment were carried out. The results illustrate that the pressure growth mode in the impeller is consistent with the channels, which confirms the circulation flow existing in the pump. Furthermore, it is found that the circulation flow that features with longitudinal vortexes can be evaluated quantitatively by combining the analyses of the dimensionless axial distance, circulation number and entropy production. A smaller axial distance indicates that more flow is involved in the circulation and the intensity of the longitudinal vortex is enhanced; a large circulation number accompanied by a small dissipation loss could result in a satisfactory exchange flow. Therefore, the largest circulation number, least amount of dissipation, and shortest distance lead to the highest head and efficiency in the model with V-shaped blades and an increased impeller height. This work establishes a deeper understanding of the energy exchange mechanism and could serve as a reference for the geometrical design and performance reinforcement of RFP.

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