Water Film Production on 3-D Airfoil Surface CFD Simulation
The present problem simulates the water film production on the surface of the airfoil body using ANSYS Fluent software.
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Water Film Production Project Description
The present problem simulates the air flow around the airfoil and create a water film on the surface of the airfoil body using ANSYS Fluent software. In fact, when moisturized air and water droplets hits the surface of the airfoil, a water film may form on the airfoil surface. The purpose of this work is to investigate the thickness of the produced and flowing fluid layer on the airfoil body; This is because the presence of this layer of film on the fuselage of the aircraft can cause water droplets to freeze on the surface of the airfoil at very low temperatures.
The Eulerian wall film (ewf) model was used to simulate and estimate the amount of liquid film produced. This model is used to estimate the formation or flow of a thin film of liquid on the wall surfaces. This model can only be used for 3D geometric models and to use it, the Eulerian multi phase model must be activated. Unlike other models in the software (such as VOF model and radiation model, etc.), the Eulerian wall film model has the ability to correct the initial boundary conditions on the walls and, therefore, has a good interaction with the liquid films.
In the present simulation, the primary phase of the Eulerian model is air and its secondary phase is liquid water droplets, which are also defined as the constituents of the Eulerian liquid film. The mixture of air flow and water droplets moves towards the airfoil body at a speed of 30 m.s-1 and a temperature of 250 K; So that the volume fraction of water droplets is equal to 0.002. The boundary condition of the airfoil wall is defined in such a way that in the initial state, the liquid film has a specific height and zero velocity. The simulation process was performed in 1s with a time step size equal to 0.0001s.
Airfoil Geometry & Mesh
The present model is designed in three dimensions using Design Modeler software. The model consists of a rectangular cube computational domain measuring 5 m * 2 m * 3 m in which a three-dimensional airfoil with a depth of 1m is located. To draw this airfoil, the set of coordinates of the points that form the curvature of the surface of the airfoil body should be imported to the software, named cloud points.
The meshing of the model has been done using ANSYS Meshing software and the mesh type is unstructured. The element number is 978532. The following figure shows the mesh.
Water Film CFD Simulation
To simulate the present model, several assumptions are considered:
- We perform a pressure-based solver.
- The simulation is unsteady. Because changes in the thickness of Eulerian film have been investigated over time.
- The gravity effect on the fluid is equal to -9.81 m.s-2 along the Y-axis.
A summary of the defining steps of the problem and its solution is given in the following table:
|number of eulerian phases||2 (air & water)|
|Eulerian Wall Film||Eulerian Film Model|
|surface tension||0.07194 n.m-1|
|phase velocity||5 m.s-1|
|phase concentration||0.01 kg.m-3|
|gauge pressure||0 pascal|
|air||velocity magnitude||30 m.s-1|
|water||velocity magnitude||30 m.s-1|
|flow rate weighting||1|
|Wall of Airfoil||Wall|
|wall motion||stationary wall|
|film condition type||initial condition|
|Pressure-Velocity Coupling||Phased Coupled Simple|
|momentum||first order upwind|
|volume fraction||first order upwind|
|energy||first order upwind|
|gauge pressure||0 pascal|
|x-velocity for air & water||30 m.s-1|
|temperature for air & water||250 K|
|volume fraction for air||0.998|
|volume fraction for water||0.002|
At the end of the solution process, two-dimensional contours related to density, pressure, water velocity, air velocity, water volume fraction and air volume fraction are obtained. The contour of the thickness of the film created on the body of the airfoil is also obtained. All contours correspond to the last second of the simulation process.
All files, including Geometry, Mesh, Case & Data, are available in Simulation File. By the way, Training File presents how to solve the problem and extract all desired results.