Partially Cavitating Hydrofoils: Experimental and Numerical Analysis*

2000 ◽  
Vol 44 (01) ◽  
pp. 40-58
Author(s):  
Christian Pellone ◽  
Thierry Maître ◽  
Laurence Briançon-Marjollet
Keyword(s):  
Numerical Models ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Navier Stokes ◽  
Viscous Effects ◽  
Local Pressure ◽  
Two Phase ◽  
Complete Study ◽  
Flow Configurations ◽  
Potential Methods

The numerical modeling of partially cavitating foils under a confined flow configuration is described. A complete study of previous numerical models highlights that the presence of a turbulent and two-phase wake, at the rear of the cavity, has a nonnegligible effect on the local pressure coefficient, the cavitation number, the cavity length and the lift coefficient; hence viscous effects must be included. Two potential methods are used, each being coupled with a calculation of the boundary layer developed downstream of the cavity. So, an "open cavity" numerical model, as it is called, was developed and tested with two types of foil: a NACA classic foil and a foil of which the profile is obtained performing an inverse calculation on a propeller blade test section. On the other hand, under noncavitating conditions, for each method, the results are compared with the results obtained by the Navier-Stokes solver "FLUENT." The cavitating flow configurations presented herein were carried out using the small hydrodynamic tunnel at Bassin d'Essais des Carènes [Val de Reuil, France]. The results obtained by the two methods are compared with experimental measurements.

scholarly journals Study on Influencing Factors of Helicopter Brownout Evolution Based on CFD-DEM

2021 ◽  
Vol 12 (1) ◽  
pp. 126
Author(s):  
Yihua Cao ◽  
Gaozhan Wang ◽  
Chongwen Jiang
Keyword(s):  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Element Model ◽  
Tip Vortex ◽  
Movement Speed ◽  
Two Phase ◽  
Sliding Mesh ◽  
Lagrangian Framework ◽  
Blade Section ◽  
Sand Dust

The gas-solid two-phase flow model is constructed based on the Euler-Lagrangian framework. The SST k−ω two-equation turbulence model and the soft ball model are coupled by computational fluid dynamics (CFD) and a discrete element model (DEM). Brownout is then simulated by the above method with sliding mesh. As the calculation examples show, the simulations and experiments of the Lynx rotor and the Caradonna–Tung rotor are compared. The coupling method is verified through calculation of the rotor lift coefficient, blade section pressure coefficient and tip vortex shedding position. The results show that when the helicopter is hovering at a height of 0.52R from the ground, it will cause brownout and the pilot’s vision will be obscured by sand. When the hovering height is 1R, the phenomenon of brownout is not serious. The movement speed of most sand dust is about 12 m/s, and the height of the sand dust from the ground will gradually increase over time. Large particles of sand are more difficult to be entrained into the air than the small particles, and the particles with a radius of 50 um are basically accumulated on the ground. Moreover, the slotted-Tip rotor has an effect on restraining brownout.

Roll Damping Simulations of an Offshore Heavy Lift DP3 Installation Vessel Using the CFD Toolbox OpenFOAM

2020 ◽  
Author(s):  
Brecht Devolder ◽  
Florian Stempinski ◽  
Arjan Mol ◽  
Pieter Rauwoens
Keyword(s):  
Boundary Element ◽  
Damping Coefficient ◽  
Navier Stokes ◽  
Roll Motion ◽  
Viscous Effects ◽  
Roll Damping ◽  
Two Phase ◽  
Damping Behavior ◽  
External Moment ◽  
Heavy Lift

Abstract In this work, the roll damping behavior of the offshore heavy lift DP3 installation vessel Orion from the DEME group is studied. Boundary element codes using potential flow theory require a roll damping coefficient to account for viscous effects. In this work, the roll damping coefficient is calculated using the Computational Fluid Dynamics (CFD) toolbox OpenFOAM. The two-phase Navier-Stokes fluid solver is coupled with a motion solver using a partitioned fluid-structure interaction algorithm. The roll damping is assessed by the Harmonic Excited Roll Motion (HERM) technique. An oscillating external moment is applied on the hull and the roll motion is tracked. Various amplitudes and frequencies of the external moment and different forward speeds, are numerically simulated. These high-fidelity full-scale simulations result in better estimations of roll damping coefficients for various conditions in order to enhance the accuracy of efficient boundary element codes for wave-current-structure interactions simulations.

A Numerical Investigation of High Lift Coefficient Airfoils Near Regions of Stall

2013 ◽  
Author(s):  
Ravon Venters ◽  
Brian Helenbrook
Keyword(s):  
Experimental Data ◽  
Free Stream ◽  
Numerical Models ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Optimal Placement ◽  
Navier Stokes ◽  
Cross Sectional ◽  
High Lift ◽  
Optimal Angle

The cross-sectional geometry of a diffuser-augmented wind turbine (DAWT) is often that of a cambered airfoil oriented at an angle of attack such that the lift coefficient of the airfoil is maximal. Beyond this angle separation occurs, and the performance decreases. Thus, predicting this transition is important for creating an optimally designed diffuser. The focus of this work is to validate two numerical methods for predicting the onset of separation for highly cambered airfoils. The numerical models investigated are a Reynolds-averaged-Navier-Stokes (RANS) k–ε model and XFOIL. The results were compared to each other and to experimental data. Overall the most accurate model was the k–ε model. Using this model, an optimization of a 2D DAWT was performed which determined the optimal placement of the diffuser. This optimization showed that the optimal angle of attack for the diffuser is much greater than what one would expect based on the maximum lift angle of an airfoil in a free-stream.

Application of Modified PANS Model for Computation of Cloud Cavitation around a Clark-Y Hydrofoil

2013 ◽  
Vol 456 ◽  
pp. 173-177
Author(s):  
Wei Dong Shi ◽  
Guang Jian Zhang
Keyword(s):  
Turbulent Viscosity ◽  
Lift Coefficient ◽  
Correction Function ◽  
Navier Stokes ◽  
Two Phase ◽  
Cloud Cavitation ◽  
Cavity Shedding ◽  
Time Average ◽  
Phase Mixture ◽  
Experimental Values

A density correction function was introduced to the Partially-Averaged Navier-Stokes Model (PANS) taking into account the local compressibility of two-phase mixture. The standard k-ε model, PANS model and the modified PANS model were used to simulate the unsteady cloud cavitation around a Clark-y hydrofoil and the evolutions of cavity shape, time-averaged turbulence viscosity distribution and lift coefficient variation were investigated. The results compared with experimental data show that the PANS model and the modified PANS model strongly reduce the turbulent viscosity and predict the cloud cavity shedding behavior observed in the experiment successfully, while the cavitation area and time-average lift coefficient predicted by the modified PANS model is closer to the experimental values than the original PANS model.

Validation of RANS Turbulence Models for Labyrinth Seal Flows by Means of Particle Image Velocimetry

2020 ◽  
Author(s):  
Lars Wein ◽  
Tim Kluge ◽  
Joerg R. Seume ◽  
Rainer Hain ◽  
Thomas Fuchs ◽  
...  
Keyword(s):  
Velocity Field ◽  
Numerical Models ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Labyrinth Seal ◽  
Viscous Effects ◽  
Local Pressure ◽  
Wrong Prediction ◽  
Rans Turbulence Models ◽  
Rate Of Dissipation

Abstract Accurate prediction of labyrinth seal flows is important for the design and optimisation of turbomachinery. However, the prediction of such flows with RANS turbulence models is still lacking. The identification of modelling deficits and the development of improved turbulence models requires detailed experimental data. Consequently, a new test rig for straight labyrinth seals was built at the Institute for Turbomachinery and Fluid Dynamics which allows for non-intrusive measurements of the three dimensional velocity field in the cavities. Two linear eddy viscosity models and one algebraic Reynolds stress turbulence model have been tested and validated against global parameters, local pressure measurements, and non-intrusive measurements of the velocity field. While some models accurately predict the discharge coefficient, large local errors occurred in the prediction of the wall static pressure in the seal. Although improved predictions were possible by using model extensions, significant errors in the prediction of vortex systems remained in the solution. These were identified with the help of PIV results. All turbulence models struggled to accurately predict the size of separations and the swirl imposed by viscous effects at the rotor surface. Additionally, the expansion of the leakage jet in the outlet cavity is not modelled correctly by the numerical models. This is caused by a wrong prediction of turbulent kinetic energy and, presumably, its rate of dissipation.

A Numerical Simulation of a Brush Seal Section and Some Experimental Results

1995 ◽  
Vol 117 (1) ◽  
pp. 190-202 ◽  
Author(s):  
M. J. Braun ◽  
V. V. Kudriavtsev
Keyword(s):  
Stokes Equations ◽  
Numerical Models ◽  
Navier Stokes ◽  
Local Pressure ◽  
Local Flow ◽  
Navier Stokes Equations ◽  
Pressure Fields ◽  
Brush Seal ◽  
Flow Phenomena ◽  
Insight Into

The brush seal technology represents quite a promising advance in the effort of construction of more efficient, and possibly smaller size engines. Conclusions of recent workshops determined that while the brush seal works well, there is a need to improve its performance characteristics. The considerable amount of experimental work performed to date has indicated the importance of the local flow phenomena in the global sealing process performance of the brush (Braun et al., 1990a, 1991b, 1992; Hendricks et al., 1991a). The distributed flow and pressure fields are thus of vital importance for the prediction of the possible sudden failure of the brush seal under unexpected local “pressure hikes.” It is in this context that the authors developed a numerical, two-dimensional time accurate dependent formulation of the Navier–Stokes equations with constant properties, and included the effects of inertia, viscous, and pressure terms. The algorithm is applied to a set of noncompliant multirow, multicolumn pin configurations that are similar to the ones found in an idealized brush seal configuration. While the numerical parametric investigation aims at establishing the occurrence of major flow patterns and associated pressure maps, the experimental portion of the paper is aimed at gaining further insight into the relevant flow structures, and thus guiding the development of the mathematical and numerical models.

Outdoor Test of Wind-Drifted Snow Distribution around a Cube

2010 ◽  
Vol 439-440 ◽  
pp. 1349-1354
Author(s):  
Ke Qin Yan ◽  
Xuan Yi Zhou ◽  
Ming Gu
Keyword(s):  
Wind Tunnel ◽  
Stokes Equations ◽  
Pressure Coefficient ◽  
Navier Stokes ◽  
Two Phase ◽  
Navier Stokes Equations ◽  
Incompressible Viscous Flow ◽  
Snow Distribution ◽  
Computational Fluid Dynamics Cfd ◽  
Outdoor Test

This paper presents the results of an outdoor investigation of wind-drifted snow distribution around a cube. The test was performed in a simple outdoor wind tunnel at Harbin in January 2009. Velocity distribution around the cube and pressure coefficient on the cube surfaces are also simulated with computational fluid dynamics (CFD). The simulation is based on homogenous two-phase flow theory, where the flow field is predicted by solving Navier-Stokes equations for transient, incompressible viscous flow. The inlet profiles of the simulation adopted data got from wind tunnel. Comparison between the test result and that of simulation shows that velocity is closely related to the snow distribution.

scholarly journals Aeration performance of high-head siphon-shaft spillways by CFD models

2021 ◽  
Vol 11 (10) ◽  
Author(s):  
M. Cihan Aydin ◽  
Ali Emre Ulu
Keyword(s):  
Volume Fraction ◽  
Numerical Models ◽  
Three Dimensional ◽  
Air Entrainment ◽  
Navier Stokes ◽  
Two Phase ◽  
Discharge Performance ◽  
Cfd Models ◽  
High Head ◽  
American Society

AbstractSiphon-shaft spillways are constituted by covering above a shaft spillway with a hood that creates siphonic pressure. This study focused on the aeration the flow through the aerator holes placed on the hood to prevent cavitational damage in high-head siphon-shaft spillways. Three-dimensional computational fluid dynamics (CFD) technique using finite-volume method to solve Reynolds-averaged Navier–Stokes (RANS) equations for the incompressible viscous and turbulent fluids motion was performed to analyze the full-scaled two-phase numerical models. The volume of fluid (VOF) scheme was used to simulate two-phase (water–air) flow, by defining the volume fraction for each of the fluids throughout the solution domain. The accuracy of the numerical model was tested using a procedure recommended by American Society of Mechanical Engineers (ASME) for CFD applications. The numerical results showed that the aeration is highly effective in reducing siphon sub-pressures and cavitation. The optimal relative aeration diameter of 0.45 provided sufficient air entrainment to protect from cavitation and did not decrease the discharge performance too much.

Design of Low-Speed Cascades for Investigating Viscous Effects in High-Speed Axial Turbines

2000 ◽  
Author(s):  
K. Zavitz ◽  
S. A. Sjolander
Keyword(s):  
Design Problem ◽  
High Speed ◽  
Pressure Coefficient ◽  
Design Procedure ◽  
Panel Method ◽  
Inverse Design ◽  
Navier Stokes ◽  
Viscous Effects ◽  
Low Speed ◽  
Inverse Design Problem

For turbine flow phenomena which are dominated by viscous effects, many valuable insights into the flow physics can be gained through low-speed cascade measurements. For example, for low-pressure turbines unsteady wake-blade interactions can be investigated in cascade provided that the Reynolds number, freestream turbulence conditions and the pressure coefficient distributions are the same in the cascade as in the high-speed counterpart. This paper describes an iterative procedure for inversely designing low-speed linear cascades with prescribed blade pressure-coefficient distributions. The inverse-design problem is treated as an optimization problem. The optimization strategy features the use of a genetic algorithm and a gradient-type algorithm. At the end of each global iteration of the design procedure a Navier-Stokes analysis is used to see if the final cascade geometry gives the specified pressure-coefficient distribution to the desired degree of accuracy. Although the resulting cascade may be designed to the level of accuracy afforded by the Navier-Stokes analysis, the method takes advantage of the fact that the pressure distribution in the low-speed cascade can be predicted with good accuracy and very rapidly using a panel method solution for the potential flow through the cascade. A panel method flow solver is used to minimize the number of Navier-Stokes evaluations to three or four for a given inverse-design problem. As a result, the present procedure is very efficient.

The Influence of Rotating Wheels on Vehicle Aerodynamics

2012 ◽  
Vol 246-247 ◽  
pp. 543-547 ◽  
Author(s):  
Ting Li ◽  
Qing Jia ◽  
Zhi Gang Yang
Keyword(s):  
Drag Coefficient ◽  
Lift Coefficient ◽  
Computational Simulation ◽  
Pressure Coefficient ◽  
Flow Characteristics ◽  
Aerodynamic Performance ◽  
Navier Stokes ◽  
Global Flow ◽  
Flow Surface ◽  
Vehicle Aerodynamics

Full scaled simplified model and production vehicle were applied to make a research on the local and global flow characteristics. Two different conditions including stationary and rotation were employed in computational simulation by steady RNS Navier-Stokes calculation. Further, detailed analysis on flow, surface pressure coefficient, drag coefficient and lift coefficient affected by rotating wheel figure out that rotating wheel has a significant influence on the flow around wheel and vehicle. Pressure difference, drag coefficient and lift coefficient are decreased by rotation, which improve aerodynamic performance.

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