Numerical Experiments for Flow Around a Ducted Tip Hydrofoil

2002 ◽  
Author(s):  
Hildur Ingvarsdo´ttir ◽  
Carl Ollivier-Gooch ◽  
Sheldon I. Green
Keyword(s):  
Turbulence Model ◽  
Vortex Core ◽  
Vortex Flow ◽  
Computational Study ◽  
Near Field ◽  
Vortex Formation ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Computational Studies ◽  
Tip Vortices

The performance and cavitation characteristics of marine propellers and hydrofoils are strongly affected by tip vortex behavior. A number of previous computational studies have been done on tip vortices, both in aerodynamic and marine applications. The focus, however, has primarily been on validating methods for prediction and advancing the understanding of tip-vortex formation in general, rather than showing effects of tip modifications on tip vortices. Studies of the most relevance to the current work include computational studies by Dacles-Mariani et al. (1995) and Hsiao and Pauley (1998, 1999). Daeles-Mariani et al. carried out interactively a computational and experimental study of the wingtip vortex in the near field using a full Navier-Stokes simulation, accompanied with the Baldwin-Barth turbulence model. Although they showed improvement over numerical results obtained by previous researchers, the tip vortex strength was underpredicted. Hsiao and Pauley (1998) studied the steady-state tip vortex flow over a finite-span hydrofoil, also using the Baldwin-Barth turbulence model. They were able to achieve good agreement in pressure distribution and oil flow pattern with experimental data and accurately predict vertical and axial velocities of the tip vortex core within the near-field region. Far downstream, however, the computed flow field was overly diffused within the tip vortex core. Hsiao and Pauley (1999) also carried out a computational study of the tip vortex flow generated by a marine propeller. The general characteristics of the flow were well predicted but the vortex core was again overly diffused.

Prediction of Propeller Tip Vortex Using OpenFOAM

2017 ◽  
Author(s):  
Md Ashim Ali ◽  
Heather Peng ◽  
Wei Qiu ◽  
Rickard Bensow
Keyword(s):  
Vortex Core ◽  
Eddy Viscosity ◽  
Vortex Flow ◽  
Unstructured Grid ◽  
Turbulence Models ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Taylor Model ◽  
Navier Stokes Equation ◽  
Thrust And Torque

It is important to predict the propeller tip vortex flow and its effect on hull vibration and noise. In our previous work, the tip vortex flow of the David Taylor Model Basin (DTMB) 5168 propeller model has been studied based on the Reynolds Averaged Navier-Stokes equation (RANS) solution using various eddy viscosity and Reynolds Stress turbulence models. A set of structural grids were used, however, large Jacobian values of the structural grids around the propeller tip region led to the convergence problem and inaccurate solutions. In the present work, the numerical prediction of the same propeller model was improved by using a steady-state RANS solver simpleFoam in OpenFOAM with locally refined unstructured grid along the tip vortex trajectory. The computed thrust and torque coefficients and the velocity components across the vortex core are compared with experimental data and results in the previous studies. Improvement in the prediction of velocity components across the tip vortex core were achieved.

Computational Study of Unsteady Cavitating Vortex Flow in Axisymmetric Submerged Water Jet

2005 ◽  
Author(s):  
Guoyi Peng
Keyword(s):  
High Speed ◽  
Vortex Flow ◽  
Computational Study ◽  
Near Field ◽  
Vortex Formation ◽  
Water Jet ◽  
Formation Time ◽  
Two Phase ◽  
Cavitation Bubbles ◽  
Vortex Formation Time

Unsteady cavitating and non-cavitating flows of high-speed submerged water jet have been investigated numerically by applying an approach based on the two-phase cavitation model to clarify the behavior of cavitating vortex flow in the near field of jet. The cavitation intensity is calculated by VOF method accounting for expanding and contracting of cavitation bubbles with the barotropic relation and the unsteady flow is calculated by RANS method employing the RNG k-ε turbulence model under the assumption of locally homogeneous two-phase flow. Computations are focused on the behavior of starting jet, and the validity is confirmed by comparing with experimental data. The result shows that a starting vortex ring is generated around the jet periphery, and develops with the vortex formation time. The relative standoff distance of ring-like cavity of cavitation bubbles generated in the starting vortex increases with the dimensionless vortex formation time similarly under different injection velocities.

Study of Tip Vortex Cavitation Inception Using Navier-Stokes Computation and Bubble Dynamics Model

1999 ◽  
Vol 121 (1) ◽  
pp. 198-204 ◽  
Author(s):  
Chao-Tsung Hsiao ◽  
Laura L. Pauley
Keyword(s):  
Vortex Core ◽  
Bubble Dynamics ◽  
Three Dimensional ◽  
Window Size ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Cavitation Inception ◽  
Flow Effects ◽  
Bubble Sizes ◽  
Real Flow

The Rayleigh-Plesset bubble dynamics equation coupled with the bubble motion equation developed by Johnson and Hsieh was applied to study the real flow effects on the prediction of cavitation inception in tip vortex flows. A three-dimensional steady-state tip vortex flow obtained from a Reynolds-Averaged Navier-Stokes computation was used as a prescribed flow field through which the bubble was passively convected. A “window of opportunity” through which a candidate bubble must pass in order to be drawn into the tip-vortex core and cavitate was determined for different initial bubble sizes. It was found that bubbles with larger initial size can be entrained into the tip-vortex core from a larger window size and also had a higher cavitation inception number.

Scaling of Tip Vortex Cavitation Inception Noise With a Bubble Dynamics Model Accounting for Nucleus Size Distribution

2003 ◽  
Author(s):  
Chao-Tsung Hsiao ◽  
Georges L. Chahine
Keyword(s):  
Size Distribution ◽  
Vortex Flow ◽  
Bubble Dynamics ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Nucleus Size ◽  
Scaling Effects ◽  
Dynamics Model ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception

A Surface-Averaged Pressure (SAP) spherical bubble dynamics model accounting for a statistical nuclei size distribution was used to model the acoustic signals generated by cavitating bubbles near inception in a tip vortex flow. The flow field generated by finite-span elliptic hydrofoils is obtained by Reynolds-Averaged Navier-Stokes computations. An “acoustic” criterion which defines the cavitation inception by counting the number of acoustical signal peaks that exceed a certain level per unit time was applied to deduce the cavitation inception number for different scales. It was found that the larger scale results in more cavitation inception events per unite time because more nuclei are excited by the tip vortex at the larger scale. The nuclei size was seen to have an important effect on cavitation inception number with scaling effects due to nuclei increasing as nuclei sizes decreases.

Effect of Blade Tip Modifications for Unducted Propulsors on Tip Vortex-Rotor Interaction Noise

2014 ◽  
Author(s):  
Florian Danner ◽  
Christofer Kendall-Torry
Keyword(s):  
Rotor Blade ◽  
Stokes Equations ◽  
Acoustic Emissions ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Tip Vortices ◽  
Blade Tip ◽  
Blade Loads ◽  
Blade Tips

Front rotor tip vortices impinging on a downstream blade row of an unducted propulsor induce distinct unsteadiness to blade loads with associated sound emissions. Since the region of unsteadiness is concentrated near the blade tips, reducing the rear rotor tip diameter represents a potential means for minimising interaction noise. A survey on the aeroacoustic effects resulting from a cropped rear rotor in combination with a front rotor blade tip modification is therefore presented. Analyses are based on data from computational fluid dynamics solutions with the Reynolds-averaged Navier-Stokes equations and direct acoustic predictions. The evaluation of polar directivities, blade surface pressure disturbances and details of the unsteady flow field provide insight into the underlying phenomena. Results show that an arbitrary reduction of the rear rotor tip diameter does not necessarily decrease noise radiation and that winglet-like structures applied to the front rotor blade tips are capable of reducing acoustic emissions due to tip vortex-rotor interactions.

scholarly journals Numerical and experimental investigation of the mean and turbulent characteristics of a wing-tip vortex in the near field

2014 ◽  
Vol 228 (13) ◽  
pp. 2516-2529 ◽  
Author(s):  
Micheál S O’Regan ◽  
Philip C Griffin ◽  
Trevor M Young
Keyword(s):  
Reynolds Stress ◽  
Turbulence Model ◽  
Near Field ◽  
Tip Vortex ◽  
Mean Flow ◽  
Turbulent Characteristics ◽  
The Mean ◽  
Wing Tip Vortex ◽  
Wing Tip ◽  
Good Agreement

The near-field (up to three chord lengths) development of a wing-tip vortex is investigated both numerically and experimentally. The research was conducted in a medium speed wind tunnel on a NACA 0012 square tip half-wing at a Reynolds number of 3.2 × 105. A full Reynolds stress turbulence model with a hybrid unstructured grid was used to compute the wing-tip vortex in the near field while an x-wire anemometer and five-hole probe recorded the experimental results. The mean flow of the computed vortex was in good agreement with experiment as the circulation parameter was within 6% of the experimental value at x/ c = 0 for α = 10° and the crossflow velocity magnitude was within 1% of the experimental value at x/ c = 1 for α = 5°. The trajectory of the computed vortex was also in good agreement as it had moved inboard by the same amount (10% chord) as the experimental vortex at the last measurement location. The axial velocity excess is under predicted for α = 10°, whereas the velocity deficit is in relatively good agreement for α = 5°. The computed Reynolds shear stress component 〈 u′v′〉 is in good agreement with experiment at x/ c = 0 for α = 5°, but is greatly under predicted further downstream and at all locations for α = 10°. It is thought that a lack of local grid refinement in the vortex core and deficiencies in the Reynolds stress turbulence model may have led to errors in the mean flow and turbulence results respectively.

Numerical Computation of Tip Vortex Flow Generated by a Marine Propeller

1999 ◽  
Vol 121 (3) ◽  
pp. 638-645 ◽  
Author(s):  
Chao-Tsung Hsiao ◽  
Laura L. Pauley
Keyword(s):  
Cross Section ◽  
Vortex Flow ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Marine Propeller ◽  
Mean Velocity ◽  
Cavitation Inception ◽  
Section Design ◽  
The Mean ◽  
Propeller Performance

The uniform flow past a rotating marine propeller was studied using incompressible Reynolds-averaged Navier-Stokes computations with the Baldwin-Barth turbulence model. Extensive comparison with the experimental data was made to validate the numerical results. The general characteristics of the propeller flow were well predicted. The current numerical method, however, produced an overly diffusive and dissipative tip vortex core. Modification of the Baldwin-Barth model to better predict the Reynolds stress measurements also improved the prediction of the mean velocity field. A modified tip geometry was also tested to show that an appropriate cross section design can delay cavitation inception in the tip vortex without reducing the propeller performance.

Vortex Ring Model of Tip Vortex Aperiodicity in a Hovering Helicopter Rotor

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
Anand Karpatne ◽  
Jayant Sirohi ◽  
Swathi Mula ◽  
Charles Tinney
Keyword(s):  
Vortex Core ◽  
Distribution Functions ◽  
Tip Vortex ◽  
Helicopter Rotor ◽  
Time Step ◽  
Tip Vortices ◽  
Ring Model ◽  
Image Velocimetry ◽  
Blade Tip ◽  
Stereo Particle Image Velocimetry

The wandering motion of tip vortices trailed from a hovering helicopter rotor is described. This aperiodicity is known to cause errors in the determination of vortex properties that are crucial inputs for refined aerodynamic analyses of helicopter rotors. Measurements of blade tip vortices up to 260 deg vortex age using stereo particle-image velocimetry (PIV) indicate that this aperiodicity is anisotropic. We describe an analytical model that captures this anisotropic behavior. The analysis approximates the helical wake as a series of vortex rings that are allowed to interact with each other. The vorticity in the rings is a function of the blade loading. Vortex core growth is modeled by accounting for vortex filament strain and by using an empirical model for viscous diffusion. The sensitivity of the analysis to the choice of initial vortex core radius, viscosity parameter, time step, and number of rings shed is explored. Analytical predictions of the orientation of anisotropy correlated with experimental measurements within 10%. The analysis can be used as a computationally inexpensive method to generate probability distribution functions for vortex core positions that can then be used to correct for aperiodicity in measurements.

On the roll-up of a trailing vortex sheet in the very near field

2003 ◽  
Vol 217 (5) ◽  
pp. 263-269 ◽  
Author(s):  
A L Heyes ◽  
S J Hubbard ◽  
A J Marquis ◽  
D A Smith
Keyword(s):  
Vortex Core ◽  
Near Field ◽  
Angle Of Attack ◽  
Point Vortex ◽  
Vortex Sheet ◽  
Measured Data ◽  
Tip Vortex ◽  
Two Dimensional ◽  
Trailing Edge ◽  
Naca 0012

This paper addresses a discrepancy found between the rate of roll-up of a trailing vortex sheet calculated from point vortex simulations and that from measured data. Measurements of the wake behind a rectangular planform NACA 0012 section wing at 7.5° angle of attack show that some 50 per cent of the circulation in the wake is already present in the vortex core or “rolled-up region” at the trailing edge of the wing, and that there is no increase in the circulation contained within this region within one chord length downstream of the trailing edge. This conflicts with two-dimensional point vortex simulations of sheet roll-up which predict no initial core at the trailing edge and a constantly increasing value of circulation in the vortex in the downstream direction. A modification to include the effect of the tip vortex in the simulation is proposed and is shown to represent the behaviour of the vortex sheet in the very near field accurately.

Numerical investigation of transverse sonic injection in a non-reacting supersonic combustor

2005 ◽  
Vol 219 (3) ◽  
pp. 205-215 ◽  
Author(s):  
P Manna ◽  
D Chakraborty
Keyword(s):  
Turbulence Model ◽  
Stokes Equations ◽  
Near Field ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Supersonic Stream ◽  
Scramjet Combustor ◽  
The Difference ◽  
Experimental Values ◽  
Sonic Injection

Efficient combustion and heat release in scramjet flows depend on effective mixing of the fuel in supersonic streams. Usually, transverse sonic injection in-stages are employed as one of the suitable means for efficient supersonic combustor design. Numerical simulations are carried out to study the mixing characteristics of staged sonic air injections in supersonic stream ( M = 2.07) behind a backward-facing step in scramjet combustor by solving three-dimensional Navier-Stokes equations along with K-ε turbulence model with a commercial CFD software CFX-TASCFlow. Computed results of the jet penetration and spreading show very good agreement with the experimental values and the results of other computations. A good overall match has been obtained between the experimental values and the computation for various flow profiles at various axial locations in the combustor. However, the values differ in the near-field region at the injection plane. The assumed uniformity of the flow-field properties at the injection orifice and/or the inadequacy of the turbulence model considered in this study is conjectured to be the cause of the difference.

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