Cavitation – NACA66 hydrofoil

Introduction

This is a validation problem of cavitation around a NACA66 hydrofoil.

The geometry and conditions from the following papers, which are often used for validation of cavitation problems, are used.

Viscous and Nuclei Effects on Hydrodynamic Loadings and Cavitation of NACA66(MOD) Foil section, Y.T.Shen, P.E. Dimotakis, J. Fluids Eng. sep. 1989

The velocity is 2.01 m/s and the cavitation number is 0.84.

The cavitation model is Schnerr-Sauer and the coefficients are as follows.

Evaporation Coefficient : 1
Condensation Coefficient : 1
Bubble Diameter : 2e-6
Bubble Number Density : 1.6e+9
Vapor pressure : 2420 Pa

Start BaramFlow and load mesh

Run the program and select ‘New Case’ from the launcher. In the launcher, select [Pressure-based] for [Solver Type] and [Volume of Fluid] for [Multiphase Model].

Use the given polyMesh folder. In the top tab, click [File]-[Load Mesh]-[OpenFOAM] in that order and select the polyMesh folder.

launcher

General

Change Time to Transient.

General

Models

For this example, we’ll use $Standard$ $k-epsilon$ model for turbulence.

Materials

Since this example is multi-phase flow, two fluids are required. You can add fluids by pressing the (+) in the top right corner of the Material Configuration section. Add waterLiquid and waterVapor.

Materials

Cell zone Conditions

In Cell Zone Conditions, there is region0 (multiple regions are displayed when it is multi-region). Set the fluid of the region.

Double-click region0 to open the setting window. Specify the Primary Material as waterVapor and the Secondary material as waterLiquid.

Use 0.07 for Surface Tension.

Turn on the Cavitation option. Select Schnerr-Sauer for Model and enter 2430 for Vaporization Pressure. Use the following values for Model Constants

Evaporation Coefficient : 1
Condensation Coefficient : 1
Bubble Diameter : 2.0e-06
Bubble Number Density : 1.6e+9

Cell Zone Conditions

Boundary Conditions

Set the boundary type and values as shown below.

B_INLET
- type : Velocity Inlet
- Velocity Magnitude : 2.01
- Turbulent Intensity : 1
- Turbulent Viscosity Ratio : 10
- Volume Fraction(water) : 1

B_INLET

B_OUTLET
- type : Pressure Outlet
- Pressure : 4113.788

B_OUTLET

B_SYM
- type : Symmetry
FOIL_DOWN, FOIL_UP
- type : Wall
EMPTY
- type : Empty

Numerical Conditions

In this example, we’ll change the settings as shown below.

Pressure-Velocity Coupling Scheme : SIMPLE
Use Momentum Predictor : On
Discretization Schemes
- Time : First Order Implicit
- Pressure : Momentum Weighted Reconstruct
- Momentum : Second Order Upwind
- Turbulence : First Order Upwind
- Volume Fraction : Second Order Upwind
Under-Relaxation Factors : use default values
Improve Stability : Off
Max Iteration per Time Step : 10
Number of Correctors : 2
Multiphase와 Convergence Criteria : use default values

Numerical Conditions

Initialization

Set values as follows

velocity : (2.01 0 0)
Pressure : 4113.788
Scale of Velocity : 2.01
Turbulent Intensity : 1
Turbulent Viscosity Ratio : 10
Volume Fraction(water) : 1

initial values

Enter the value and click the Initialize button at the bottom. Then click the [File]-[Save] menu to save the case file.

Run

Change the values as shown below, and click [Start Calculation] button.

Time Stepping Method : Fixed
Time Step Size : 0.01
End time : 10
Save Interval : 0.5
Selct [Parallel]-[Environment] in menu. Set Number of Cores as you want and select [Local Machine] for [Parallel Type]

Post-processing

Click the parview button in [External tools] to open the paraview.

For parallel, change the [Case Type] to [Decomposed Case].

Change [Coloring] to p_rgh or alpha.waterLiquid.

To get the pressure data of the hydrofoil surface, select only the desired boundary (FOIL-UP) and run File-Save Data from the menu to get the data file in csv format.