Analyzing running wet and run back on wing and collection efficiency calculation
Collection efficiency (or catch efficiency) parameter is very important in aircraft icing analysis. This surface quantity is defined as the ratio of the mass-flux of the impinging droplets to the mass-flux in the free stream. Finding the collection/impingement characteristics of the aircraft body enables us to perform anti-icing or ice build-up calculations.
Running Wet and Run Back Simulations Using EWF Model
When we use anti-icing system, supercooled droplets form a water film on the surface of the aircraft body. This film runs over the surface and can release as water droplet particles due to the high shear. In order to predict collection efficiency and simulate running wet and run back problems, we employ Eulerian Wall Film (EWF) model.
It is possible to couple this model with:
- Discrete Phase Model – In this case, particles aggregate on the wall to form the film.
- Eulerian Multiphase Model –In this case, the film is formed on the wall by secondary phase mass.
EWF model uses a virtual film on the surface instead of mesh normal to the surface. The focus of thin film modeling is to model a thin film flow which can separate, strip and evaporate without affecting the core flow-field. Thin film modeling with these characteristics is computationally expensive. Because we need to use very fine mesh and calculate inter-phase flux accurately.
We can use EWF model with the 3d solver. This model also assumes that film always flows parallel to the surface and therefore the normal component of film velocity is zero. In addition, The film has a parabolic velocity profile & bilinear temperature profile across its depth.
Problem Description of Collection Efficiency Calculation
Here we model the running film on a NACA-0012 airfoil and determine the collection efficiency. The problem parameters are as follows. The Airfoil is at 5 degrees angle of attack, Mach 0.4 with a Liquid Water Content (LWC) of 1g/m^3 in freestream.
You will also learn how to do the following through this tutorial:
- Creating a film by couple EWF model with Eulerian multiphase approach
- Determine collection efficiency using EWF model
- Modeling particle stripping
- Observing particles separated or stripped from the film
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