Assessment of the Reliability of Two-Equation URANS Models in Predicting a Precessing Flow

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Xiao Chen ◽  
Zhao F. Tian ◽  
G. J. Nathan
Keyword(s):  
Velocity Field ◽  
Navier Stokes ◽  
Field Energy ◽  
Complex Flow ◽  
Systematic Assessment ◽  
Sst Model ◽  
Flow Features ◽  
Velocity Decay ◽  
Flow Through ◽  
Good Agreement

A systematic assessment of unsteady Reynolds-averaged Navier–Stokes (URANS) models in predicting the complex flow through a suddenly expanding axisymmetric chamber is reported. Five types of URANS models assessed in the study comprise the standard k–ε model, the modified k–ε (1.6) model, the modified k–ε (1.3) model, the renormalization group (RNG) k–ε model, and the shear stress transport (SST) model. To assess the strengths and limitations of these models in predicting the velocity field of this precessing flow, the numerical results are assessed against available experimental results. Good agreement with the flow features and reasonable agreement with the measured phase-averaged velocity field, energy of total fluctuation and precession frequency can be achieved with both the standard k–ε and the SST models. The degree of accuracy in predicting the rate of both spreading and velocity decay of the jet was found to greatly influence the prediction of the precession motion.

On LES Methods Applied to Seal Geometries

2012 ◽  
Author(s):  
James Tyacke ◽  
Richard Jefferson-Loveday ◽  
Paul Tucker
Keyword(s):  
Maximum Error ◽  
Labyrinth Seal ◽  
Navier Stokes ◽  
Final Solution ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy ◽  
Rans Models ◽  
Flow Through

Nine Large Eddy Simulation (LES) methods are used to simulate flow through two labyrinth seal geometries and are compared with a wide range of Reynolds-Averaged Navier-Stokes (RANS) solutions. These involve one-equation, two-equation and Reynolds Stress RANS models. Also applied are linear and nonlinear pure LES models, hybrid RANS-Numerical-LES (RANS-NLES) and Numerical-LES (NLES). RANS is found to have a maximum error and a scatter of 20%. A similar level of scatter is also found among the same turbulence model implemented in different codes. In a design context, this makes RANS unusable as a final solution. Results show that LES and RANS-NLES is capable of accurately predicting flow behaviour of two seals with a scatter of less than 5%. The complex flow physics gives rise to both laminar and turbulent zones making most LES models inappropriate. Nonetheless, this is found to have minimal tangible results impact. In accord with experimental observations, the ability of LES to find multiple solutions due to solution non-uniqueness is also observed.

scholarly journals ICCM2015: A Comparison of RANS and LES Computational Methods in Analyzing Ventilation Flow Through a Room Fitted with a Two-Sided Windcatcher

2017 ◽  
Vol 14 (03) ◽  
pp. 1750021 ◽  
Author(s):  
A. Niktash ◽  
B. P. Huynh
Keyword(s):  
Natural Ventilation ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Interior Space ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Through ◽  
Cfd Method ◽  
Good Agreement

A windcatcher is a structure for providing natural ventilation using wind power; it is usually fitted on the roof of a building to exhaust the inside stale air to the outside and supplies the outside fresh air into the building interior space working by pressure difference between outside and inside of the building. In this paper, the behavior of free wind flow through a three-dimensional room fitted with a centered position two-canal bottom shape windcatcher model is investigated numerically, using a commercial computational fluid dynamics (CFD) software package and LES (Large Eddy Simulation) CFD method. The results have been compared with the obtained results for the same model but using RANS (Reynolds Averaged Navier–Stokes) CFD method. The model with its surrounded space has been considered in both method. It is found that the achieved results for the model from LES method are in good agreement with RANS method’s results for the same model.

Evaluation of Unsteady CFD Methods by Their Application to a Transonic Propfan Stage

2001 ◽  
Author(s):  
S. Schmitt ◽  
F. Eulitz ◽  
L. Wallscheid ◽  
A. Arnone ◽  
M. Marconcini
Keyword(s):  
Numerical Methods ◽  
Navier Stokes ◽  
Test Case ◽  
Flow Angle ◽  
Laser Measurements ◽  
General Flow ◽  
Blade Row ◽  
Flow Features ◽  
Blade Row Interaction ◽  
Good Agreement

The accuracy in predicting the unsteady aerodynamic blade-row-interaction of two state-of-the-art Navier-Stokes codes is evaluated within the current paper. The general flow features of the test case — a transonic research propfan stage — are described in brief as far as necessary to understand the detailed comparisons. The calculated unsteady velocity and flow angle distributions at various axial planes of the stage are compared to data from unsteady laser measurements. The general flow features of the propfan are very well reproduced by the numerical methods and a good agreement is also obtained in comparison to the measured data. One important outcome of the comparison is the good agreement of both numerical methods with the unsteady fluctuations measured in the experiment.

The Effect of Blade Lean, Twist and Bow on the Performance of Axial Turbine at Design Point

2011 ◽  
Author(s):  
Hadi Karrabi ◽  
Mohsen Rezasoltani
Keyword(s):  
Stokes Equations ◽  
Numerical Data ◽  
Navier Stokes ◽  
Minor Effect ◽  
Complex Flow ◽  
Navier Stokes Equations ◽  
Axial Turbine ◽  
Twisted Blade ◽  
The Impact ◽  
Good Agreement

An investigation to understand the impact of twisted, leaned and bowed blades on the performance of axial turbine was undertaken. A CFD code, which solves the Reynolds-averaged Navier–Stokes equations, was used to compute the complex flow field of axial turbine. The code was validated against existing Hannover turbine experimental data. Numerical data showed good agreement with measured data. Finally, the effect of geometry changes, focusing on blade lean, twist and bow, on the Avon turbine blade performance, was analyzed. Results show that twisted blade affects performance significantly. Leaned and bowed blade has minor effect on performance.

scholarly journals Ability of the e-TellTale sensor to detect flow features over wind turbine blades: flow stall/reattachment dynamics

2020 ◽  
Author(s):  
Antoine Soulier ◽  
Caroline Braud ◽  
Dimitri Voisin ◽  
Bérengère Podvin
Keyword(s):  
Velocity Field ◽  
Wind Turbine ◽  
Turbine Blades ◽  
Wind Turbine Blades ◽  
Measured Velocity ◽  
Piv Measurements ◽  
Flow Features ◽  
Blade Section ◽  
Strain Gauge Sensor ◽  
Good Agreement

Abstract. Monitoring the flow features over wind turbine blades is a challenging task that has become more and more crucial. This paper is devoted to demonstrate the ability of the e-TellTale sensor to detect the flow stall/reattachment dynamics over wind turbine blades. This sensor is made of a strip with a strain gauge sensor at its base. The velocity field was acquired using TR-PIV measurements over an oscillating 2D blade section equipped with an e-TellTale sensor. PIV images were post-processed to detect movements of the strip, which was compared to movements of flow. Results show good agreement between the measured velocity field and movements of the strip regarding the stall/reattachment dynamics.

The Numerical Simulation of LNG Sloshing With an Improved Volume of Fluid Method

2004 ◽  
Author(s):  
Erwin Loots ◽  
Wouter Pastoor ◽  
Bas Buchner ◽  
Trym Tveitnes
Keyword(s):  
Numerical Simulation ◽  
Flow Problem ◽  
Volume Of Fluid ◽  
Navier Stokes ◽  
Test Results ◽  
Complex Flow ◽  
Offshore Industry ◽  
Lng Tank ◽  
Good Agreement ◽  
Made In

With the trend towards offshore LNG production and offloading, sloshing of LNG in partially filled tanks has become an important research subject for the offshore industry. LNG sloshing can induce impact pressures on the containment system and can affect the motions of the LNG carrier. So far, LNG sloshing was mainly studied using model tests with an oscillation tank. However, the development of Navier-Stokes solvers with a detailed handling of the free surface, nowadays allows the numerical simulation of sloshing. It should be investigated, however, how accurate the results of this type of simulations are for this complex flow problem. The present paper first presents the details of a numerical model, an improved Volume OF Fluid (iVOF) method. Comparisons are made with sloshing model test results. Based on the results, the following conclusions can be drawn: - The dynamics of sloshing in LNG tanks can be simulated numerically using an iVOF Navier-Stokes solver. - Several improvements have been made in the treatment of numerical spikes in the pressure signals, but still more improvements need to be made. - Qualitatively, the pressure pulses resulting from impacts against the LNG tank wall show a rather good agreement between experiment and numerical simulation. - Quantitatively, the differences with the experiment show that further detailed studies with respect to cell sizes and time steps are necessary.

Steady two-dimensional flow through a row of normal flat plates

1990 ◽  
Vol 210 ◽  
pp. 281-302 ◽  
Author(s):  
D. B. Ingham ◽  
T. Tang ◽  
B. R. Morton
Keyword(s):  
Finite Difference ◽  
Stokes Equations ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Corner Singularities ◽  
Flat Plates ◽  
Navier Stokes Equations ◽  
Flow Through ◽  
Good Agreement

A numerical and experimental study is described for the two-dimensional steady flow through a uniform cascade of normal flat plates. The Navier–Stokes equations are written in terms of the stream function and vorticity and are solved using a second-order-accurate finite-difference scheme which is based on a modified procedure to preserve accuracy and iterative convergence at higher Reynolds numbers. The upstream and downstream boundary conditions are discussed and an asymptotic solution is employed both upstream and downstream. A frequently used method for dealing with corner singularities is shown to be inaccurate and a method for overcoming this problem is described. Numerical solutions have been obtained for blockage ratio of 50 % and Reynolds numbers in the range 0 [les ]R[les ] 500 and results for both the lengths of attached eddies and the drag coefficients are presented. The calculations indicate that the eddy length increases linearly withR, at least up toR= 500, and that the multiplicative constant is in very good agreement with the theoretical prediction of Smith (1985a), who considered a related problem. In the case ofR= 0 the Navier–Stokes equations are solved using the finite-difference scheme and a modification of the boundary-element method which treats the corner singularities. The solutions obtained by the two methods are compared and the results are shown to be in good agreement. An experimental investigation has been performed at small and moderate values of the Reynolds numbers and there is excellent agreement with the numerical results both for flow streamlines and eddy lengths.

scholarly journals Numerical Calculations of a Turbine Volute Using a 3-D Navier-Stokes Solver

1996 ◽  
Author(s):  
R. F. Martinez-Botas ◽  
K. R. Pullen ◽  
F. Shi
Keyword(s):  
Three Dimensional ◽  
Circular Cross Section ◽  
Staggered Grid ◽  
Navier Stokes ◽  
Complex Flow ◽  
Numerical Predictions ◽  
Flow Features ◽  
Simplec Algorithm ◽  
Complicated Geometry ◽  
High Reynolds

The turbine volute is a complex flow device, about which a few papers on both measurements and CFD predictions have appeared. The main reasons for the difficulties being the complicated geometry which hinders measurements to be taken by both intrusive and non-intrusive techniques, and makes the numerical predictions difficult. In this paper, the complex three-dimensional flow through a turbine volute with non-symmetric circular cross-section is studied by using a 3-D Navier-Stokes solver which has been developed by the authors. In this solver, the fully 3-D Reynolds averaged N-S equations coupled with high Reynolds number k-ε turbulence model together with the wall function under arbitrary curvilinear coordinate system are solved. The Semi-Implicit Method for Pressure-Linked Equations (SIMPLEC algorithm) with the non-staggered grid arrangement is used. In order to eliminate the decoupling between the velocity and pressure under non-staggered grid system, the physical covariant velocity component is selected as dependent variable in momentum equations and a momentum interpolation approach is employed. The validity of the free-vortex assumption is reviewed. The computation results are compared with a set of experiments performed previously by one of the authors. The flow features in the volute are discussed.

Dynamic Coefficients of Labyrinth Gas Seals: A Comparison of Experimental Results and Numerical Calculations

2000 ◽  
Author(s):  
K. Kwanka ◽  
J. Sobotzik ◽  
R. Nordmann
Keyword(s):  
Stokes Equations ◽  
Labyrinth Seal ◽  
Navier Stokes ◽  
Labyrinth Seals ◽  
Navier Stokes Equations ◽  
Rotating Speed ◽  
Dynamic Coefficients ◽  
Flow Through ◽  
Gas Seals ◽  
Good Agreement

Non-contacting labyrinth seals are still the most common constructive elements used to minimize leakage losses in turbomachinery between areas with high pressure and areas with low pressure. Unfortunately, the leakage flow through the labyrinth seal generates forces which can have a great impact on the dynamics of the turborotor. Particularly in cases of instability, the turbomachinery is restricted in its power or rotating speed because of violent self-excited vibrations of the rotor. The occurrence of self-excited rotor vibrations due to lateral forces must definitely be excluded. To consider the labyrinth forces in Finite-Element prediction, a set of preferably exact dynamic coefficients is required. Numerical approaches used to calculate the coefficients are based on Navier-Stokes equations. A comparison with experimental data is essential for a validation of the calculation. The experimental identification is difficult, because of the littleness of the forces to be measured in gas seals. Especially the non-conservative coefficients, cross-coupled stiffness and direct damping, show a good agreement in both magnitude and trend depending on the entry swirl of the seal.

Investigation of Incompressible Flow Past Two Circular Cylinders of Different Diameters

2017 ◽  
Vol 67 (5) ◽  
pp. 487
Author(s):  
Yogesh Bhumkar ◽  
Priyank Kumar ◽  
Arnab Roy ◽  
Sudip Das ◽  
Jai Kumar Prasad
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Circular Cylinders ◽  
Navier Stokes ◽  
Complex Flow ◽  
Convective Boundary ◽  
Flow Past ◽  
Flow Features ◽  
Finite Volume Approach ◽  
Different Diameters

<p>A two - dimensional Navier-Stokes solver based on finite volume approach using a boundary-fitted curvilinear structured O-grid has been developed to obtain details of unconfined flow past cylinders at low Reynolds number of 100 and 200 based on diameter. Computations made on a single cylinder with smaller domain adopting the convective boundary conditions captured most of the flow features. This concept of a smaller domain, when used to capture the highly complex flow field around two cylinders of the same diameter placed in tandem at a Reynolds number of 200 showed reasonable results. The details of the flow field around two cylinders of different diameters placed at a typical distance of 3L and Reynolds number of 100 could be well captured adopting smaller domain concept. It is observed that the change in diameter of upstream cylinder strongly influences the overall flow field and the drag of the downstream cylinder.</p>

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