scholarly journals Experimental and Comparative RANS/URANS Investigations on the Effect of Radius of Volute Tongue on the Aerodynamics and Aeroacoustics of a Sirocco Fan

Processes ◽  
2020 ◽  
Vol 8 (11) ◽  
pp. 1442
Author(s):  
Xiaocheng Rui ◽  
Limin Lin ◽  
Junkui Wang ◽  
Xinxue Ye ◽  
Haijiang He ◽  
...  
Keyword(s):  
Flow Characteristics ◽  
Internal Flow ◽  
Adverse Pressure Gradient ◽  
Navier Stokes ◽  
Local Flow ◽  
Recirculating Flow ◽  
Reynolds Averaged Navier Stokes ◽  
Field Noise ◽  
Sirocco Fan ◽  
High Pressure Region

The geometry of volute tongue is crucial in the design of Sirocco fans. The size of the volute tongue determines its relative position and distance from the impeller which affects the local flow characteristics and thus the aerodynamic and aeroacoustic performances of the fan. In this work, we performed experimental and numerical investigations on the effect of volute tongue radius on the aerodynamic and aeroacoustic characteristics of a Sirocco fan. The internal flow characteristics are analyzed and discussed in terms of the spatial distribution and temporal variation of pressure and streamlines, the pulsating behaviors of pressure both in the impeller and on the volute surface with emphasis in the volute tongue region, the variation of passage flow with the rotation of impeller and the aeroacoustic features of the fan. We conducted numerical simulations using both steady Reynolds-Averaged Navier-Stokes (RANS) and unsteady Reynolds-Averaged Navier-Stokes (URANS) approaches with realizable k-ε turbulence model with rotation effect correction and the results are compared against the experimental data to assess the prediction capability and accuracy in qualitative and quantitative manners. Experimental and numerical results show that as the volute tongue radius increases, the static pressure rises as well as the far-field noise of the fan and pronounced fluctuation of flow is observed within the whole impeller and volute; the reversed flow in the passage of the impeller is reduced and the high-pressure region is found to be moving towards the outlet of the volute. The decreasing radius also enlarges the size of the adverse pressure gradient (APG) region on the volute tongue which contributes to the formation of recirculating flow. The comparative RANS and URANS simulations reveal that both approaches produce generally consistent results regarding the time-averaged flow although the URANS data are much closer to those of the experimental ones. However, the fluctuating flow which is not capable to be modeled by RANS still dominates for the present configuration and thus URANS is necessary for the accurate prediction of the flow details.

scholarly journals Effect of Air Injection on the Internal Flow Characteristics in the Draft Tube of a Francis Turbine Model

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1182
Author(s):  
Seung-Jun Kim ◽  
Yong Cho ◽  
Jin-Hyuk Kim
Keyword(s):  
Flow Rate ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Air Injection ◽  
Low Flow ◽  
Francis Turbine ◽  
Navier Stokes ◽  
Vortex Rope

Under low flow-rate conditions, a Francis turbine exhibits precession of a vortex rope with pressure fluctuations in the draft tube. These undesirable flow phenomena can lead to deterioration of the turbine performance as manifested by torque and power output fluctuations. In order to suppress the rope with precession and a swirl component in the tube, the use of anti-swirl fins was investigated in a previous study. However, vortex rope generation still occurred near the cone of the tube. In this study, unsteady-state Reynolds-averaged Navier–Stokes analyses were conducted with a scale-adaptive simulation shear stress transport turbulence model. This model was used to observe the effects of the injection in the draft tube on the unsteady internal flow and pressure phenomena considering both active and passive suppression methods. The air injection affected the generation and suppression of the vortex rope and swirl component depending on the flow rate of the air. In addition, an injection level of 0.5%Q led to a reduction in the maximum unsteady pressure characteristics.

scholarly journals Investigation of flow separation in a centrifugal pump impeller based on improved delayed detached eddy simulation method

2019 ◽  
Vol 11 (12) ◽  
pp. 168781401989783
Author(s):  
Yun Ren ◽  
Zuchao Zhu ◽  
Denghao Wu ◽  
Xiaojun Li ◽  
Lanfang Jiang
Keyword(s):  
Large Eddy Simulation ◽  
Centrifugal Pump ◽  
Flow Separation ◽  
Hybrid Algorithm ◽  
Internal Flow ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes ◽  
Vorticity Flux

The mechanism of flow separation in the impeller of a centrifugal pump with a low specific speed was explored by experimental, numerical, and theoretical methods. A novel delayed Reynolds-averaged Navier–Stokes/large eddy simulation hybrid algorithm combined with a rotation and curvature correction method was developed to calculate the inner flow field of the original pump for the large friction loss in the centrifugal impeller, high adverse pressure gradient, and large blade curvature. Boundary vorticity flux theory was introduced for internal flow diagnosis, and the relative velocity vector near the surface of the blade and the distribution of the dimensionless pressure coefficient was analyzed. The validity of the numerical method was verified, and the location of the backflow area and its flow features were determined. Finally, based on flow diagnosis, the geometric parameters influencing the flow state of the impeller were specifically adjusted to obtain a new design impeller. The results showed that the distribution of the boundary vorticity flux peak values, the skin friction streamline, and near-wall relative velocities improved significantly after the design change. In addition, the flow separation was delayed, the force applied on the blade was improved, the head under the part-load condition was improved, and the hydraulic efficiency was improved over the global flow ranges. It was demonstrated that the delayed Reynolds-averaged Navier–Stokes/large eddy simulation hybrid algorithm was capable to capture the separation flow in a centrifugal pump, and the boundary vorticity flux theory was suitable for the internal flow diagnosis of centrifugal pump.

Turbulence modeling effects on the aerodynamic characterizations of a NASCAR Generation 6 racecar subject to yaw and pitch changes

2019 ◽  
Vol 233 (14) ◽  
pp. 3600-3620 ◽  
Author(s):  
Chen Fu ◽  
C Patrick Bounds ◽  
Christian Selent ◽  
Mesbah Uddin
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Shear Stress ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Flow Region ◽  
Adverse Pressure Gradient ◽  
Navier Stokes ◽  
Shear Stress Transport ◽  
Reynolds Averaged Navier Stokes

The characterization of a racecar’s aerodynamic behavior at various yaw and pitch configurations has always been an integral part of its on-track performance evaluation in terms of lap time predictions. Although computational fluid dynamics has emerged as the ubiquitous tool in motorsports industry, a clarity is still lacking about the prediction veracity dependence on the choice of turbulence models, which is central to the prediction variability and unreliability for the Reynolds Averaged Navier–Stokes simulations, which is by far the most widely used computational fluid dynamics methodology in this industry. Subsequently, this paper presents a comprehensive assessment of three commonly used eddy viscosity turbulence models, namely, the realizable [Formula: see text] (RKE), Abe–Kondoh–Nagano [Formula: see text], and shear stress transport [Formula: see text], in predicting the aerodynamic characteristics of a full-scale NASCAR Monster Energy Cup racecar under various yaw and pitch configurations, which was never been explored before. The simulations are conducted using the steady Reynolds Averaged Navier–Stokes approach with unstructured trimmer cells. The tested yaw and pitch configurations were chosen in consultation with the race teams such that they reflect true representations of the racecar orientations during cornering, braking, and accelerating scenarios. The study reiterated that the prediction discrepancies between the turbulence models are mainly due to the differences in the predictions of flow recirculation and separation, caused by the individual model’s effectiveness in capturing the evolution of adverse pressure gradient flows, and predicting the onset of separation and subsequent reattachment (if there be any). This paper showed that the prediction discrepancies are linked to the computation of the turbulent eddy viscosity in the separated flow region, and using flow-visualizations identified the areas on the car body which are critical to this analysis. In terms of racecar aerodynamic performance parameter predictions, it can be reasonably argued that, excluding the prediction of the %Front prediction, shear stress transport is the best choice between the three tested models for stock-car type racecar Reynolds Averaged Navier–Stokes computational fluid dynamics simulations as it is the only model that predicted directionally correct changes of all aerodynamic parameters as the racecar is either yawed from the 0° to 3° or pitched from a high splitter-ground clearance to a low one. Furthermore, the magnitude of the shear stress transport predicted delta force coefficients also agreed reasonably well with test results.

On the Investigation of Flow around the Square Cylinder Based on Different LES Models

2012 ◽  
Vol 594-597 ◽  
pp. 2676-2679
Author(s):  
Zhe Liu
Keyword(s):  
Flow Characteristics ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Square Cylinder ◽  
Rans Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes ◽  
Les Model

Although the conventional Reynolds-averaged Navier–Stokes (RANS) model has been widely applied in the industrial and engineering field, it is worthwhile to study whether these models are suitable to investigate the flow filed varying with the time. With the development of turbulence models, the unsteady Reynolds-averaged Navier–Stokes (URANS) model, detached eddy simulation (DES) and large eddy simulation (LES) compensate the disadvantage of RANS model. This paper mainly presents the theory of standard LES model, LES dynamic model and wall-adapting local eddy-viscosity (WALE) LES model. And the square cylinder is selected as the research target to study the flow characteristics around it at Reynolds number 13,000. The influence of different LES models on the flow field around the square cylinder is compared.

Reynolds Averaged Navier Stokes Models Compared to Direct Numerical Simulations in an Adverse Pressure Gradient Boundary Layer Over a Flat Plate

2013 ◽  
Author(s):  
Daniel Routson ◽  
James Ferguson ◽  
John Crepeau ◽  
Donald McEligot ◽  
Ralph Budwig
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Flat Plate ◽  
National Laboratory ◽  
Adverse Pressure Gradient ◽  
Skin Friction Coefficient ◽  
Navier Stokes ◽  
Transition Model ◽  
Wall Functions ◽  
Reynolds Averaged Navier Stokes

In Reynolds-Averaged Navier Stokes (RANS) models simplifying assumptions breakdown in near wall regions. Wall functions/treatments become inaccurate and the homogeneity and isotropy models may not hold. To see the effect that these assumptions have on the validity of boundary layer results in a commercially available RANS code, key boundary layer parameters are compared from laminar, transitional, and fully turbulent RANS results to an existing direct numerical simulation (DNS) simulation for flow over a flat plate with an adverse pressure gradient (APG). Parameters compared include velocity profiles in the free stream, boundary layer thicknesses, skin friction coefficient and the pressure gradient parameter. Results show comparable momentum thickness and pressure gradient parameters between the transition RANS model and the DNS simulation. Differences in the onset of transition between the RANS transition model and DNS are compared as well. These simulations help evaluate the models used in the RANS code. Of most interest is the transition model, a transition shear-stress transport (SST) k–omega model. The RANS code is being used in conjunction with an APG boundary layer experiment being undertaken at the Idaho National Laboratory (INL).

Hot gas ingestion in chute rim seal clearance of gas turbine

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Xingyun Jia ◽  
Huaiyu Dong ◽  
Yuzhou Ming ◽  
Yue Wu ◽  
Lidong He
Keyword(s):  
Air Flow ◽  
Interaction Mechanism ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Navier Stokes ◽  
Marginal Effect ◽  
Pressure Potential ◽  
Hot Gas ◽  
Cooling Air Flow ◽  
Cooling Air

Abstract The Reynolds-averaged Navier–Stokes (RANS) solver was used to calculate, using a test rig to verify the accuracy. The interaction mechanism between different sealed cooling air and gas ingestion at the rotor-stator cavity and chute rim clearance has been investigated. Several groups of representative sealed cooling air flow were selected to explore the cooling efficiency, flow characteristics, tangential and radial velocity ratios in the cavity and the pressure potential field characteristics of trailing edge. The conclusions are obtained: the sealed cooling air flow rate has a significant marginal effect on the sealing effect. The gas ingestion behavior under the small sealed cooling air flow belongs to the disc cavity intrusion, and the intrusion and outflow regions at the of rim clearance are obviously divided into the intrusion characteristic section and the outflow characteristic section. The ingestion behavior under large sealed cooling air flow belongs to clearance ingestion, and the intrusion flow is limited to the chute rim clearance position, which cannot be further penetrated into the cavity. At this time, the clearance area and the cavity area become independent, and the gas ingestion characteristics depend more on the internal flow of the clearance and the vortex structure formed.

Computational Fluid Dynamics of Four-Quadrant Marine-Propulsor Flow

1999 ◽  
Vol 43 (04) ◽  
pp. 218-228
Author(s):  
Bin Chen ◽  
Frederick Stern
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Stokes Equations ◽  
Flow Characteristics ◽  
Verification And Validation ◽  
Navier Stokes ◽  
Ring Vortex ◽  
Reynolds Averaged Navier Stokes ◽  
Four Quadrant ◽  
Marine Propulsor

Computational fluid dynamics results are presented of four-quadrant flow for marine-propulsor P4381. The solution method is unsteady three-dimensional incompressible Reynolds-averaged Navier-Stokes equations in generalized coordinates with the Baldwin-Lomax turbulence model. The method was used previously for the design condition for marine-propulsor P4119, including detailed verification and validation. Only limited verification is performed for P4381. The validation is limited by the availability of four-quadrant performance data and ring vortex visualizations for the crashback conditions. The predicted performance shows close agreement with the data for the forward and backing conditions, whereas for the crashahead and crashback conditions the agreement is only qualitative and requires an ad hoc cavitation correction. Also, the predicted ring vortices for the crashback conditions are in qualitative agreement with the data. Extensive calculations enable detailed description of flow characteristics over a broad range of propulsor four-quadrant operations, including surface pressure and streamlines, velocity distributions, boundary layer and wake, separation, and tip and ring vortices. The overall results suggest promise for Reynolds-averaged Navier-Stokes methods for simulating marine-propulsor flow, including offdesign. However, important outstanding issues include additional verification and validation, time-accurate solutions, and resolution and turbulence modeling for separation and tip and ring vortices.

Unsteady Structure and Development of a Row of Impingement Jets, Including Kelvin–Helmholtz Vortex Development

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Li Yang ◽  
Phillip Ligrani ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Static Pressure ◽  
Structural Characteristics ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Axial Direction ◽  
Impinging Jets ◽  
Navier Stokes ◽  
Vortex Generation ◽  
Local Flow ◽  
Layer Parameter

Considered is a cylinder channel with a single row of ten aligned impinging jets, with exit flow in the axial direction at one end of the channel. For the present predictions, an unsteady Reynolds-Averaged Navier–Stokes (RANS) solver is employed for predictions of flow characteristics within and nearby the ten impingement jets, where the jet Reynolds number is 15,000. Spectrum analysis of different flow quantities is also utilized to provide data on associated frequency content. Visualizations of three-dimensional, unsteady flow structural characteristics are also included, including instantaneous distributions of Y-component vorticity, three-dimensional streamlines, shear layer parameter ψ, and local static pressure. Kelvin–Helmholtz vortex development is then related to local, instantaneous variations of these quantities. Of particular importance are the cumulative influences of cross flows, which result in locally increased shear stress magnitudes, enhanced Kelvin–Helmholtz vortex generation instabilities, and increased magnitudes and frequencies of local flow unsteadiness, as subsequent jets are encountered with streamwise development.

Effect of Baffles in Between Stages on Performance and Flow Characteristics of a Two-Stage Split Case Centrifugal Pump

2017 ◽  
Author(s):  
Yiyun Wang ◽  
Ji Pei ◽  
Shouqi Yuan ◽  
Wenjie Wang
Keyword(s):  
Centrifugal Pump ◽  
High Efficiency ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Production Method ◽  
Navier Stokes ◽  
Centrifugal Pumps ◽  
Two Stage

Two-stage split case centrifugal pumps play an important role in large flow rate and high lift water transfer situations. To investigate the influence of baffles in between stages on the performance and internal flow characteristics, the unsteady simulations for the prototype pump were carried out by solving the three-dimensional Reynolds-averaged Navier-Stokes equations with a shear stress transport (SST) turbulence model. The structured grids were generated for the whole flow passage. The calculated performance results were verified by the experimental measurements. The entropy production method based on numerical simulation was applied to analyze the distribution and mechanism of flow losses. The results show that the turbulence dissipation is the dominant flow loss, and the viscous dissipation can be neglected. The baffles can reduce the turbulence dissipation power obviously and can improve the hydraulic efficiency by maximum 5%, especially under QBEP and over-load conditions. The baffles have the greatest effect on the hydraulic losses in the double suction impeller., because they change the flow characteristics in the channels between the first stage impeller and the double suction impeller, affecting the inflow condition dramatically for the impeller. The study can give a reference to optimize the design of the two-stage split case centrifugal pump for high efficiency.

Aerodynamic Analysis and Design Numerical Simulation of the Vortex Flow over a Common Research Model with Flying-Wing Configuration

2014 ◽  
Vol 540 ◽  
pp. 138-142 ◽  
Author(s):  
Yong Hong Li ◽  
Yong Huang ◽  
Ji Chuan Su
Keyword(s):  
Stokes Equations ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Adverse Pressure Gradient ◽  
Aerodynamic Characteristics ◽  
Rapid Expansion ◽  
Navier Stokes ◽  
Research Model ◽  
Analysis And Design ◽  
Dominant Feature

Previous wind tunnel study has found that the lift slope of a common research model with flying-wing configuration in a transonic freestream can experience a sudden drop as the angle of attack is increased. A numerical investigation of aerodynamic characteristics of the flying-wing configuration in transonic speed flow is presented with the intend to examine the changes of the flow characteristics in detail. As can been seen from the analysis, at sufficiently high angles of attack the dominant feature of flows over the leeside of the configuration is a pair of counter-rotating vortices. Solving the steady Reynolds-Averaged Navier-Stokes equations , the flow structures were exhibited in different angles and the analysis of total pressure, static pressure and axial velocity through wing vortex cores were presented in order to analyze the flow characteristics for the develop of the vortex. The investigation shows that the numerical method is accurate enough to capture the features of the flow especially the formation and breakdown of the leading-edge vortices. The rapid expansion of the vortex core and adverse pressure gradient the flow encounters in the chordwise direction affect the aerodynamic performance severely.

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