As I mentioned in the previous post, the overall design and the concept of the glider have changed, to make it land on water. And here’s the new model.

Fig.1 CAD model of the glider

Meshing

This time around, meshing was successful thanks to its new model with smoothed out edges. The general mesh setting remained pretty much the same after the previous failure, though I’ve only set two Cartesian boxes both of witch covers the entire body and wings of the aeroplane. The surface meshing and the surface inflation went well as well as you can probably see in the image below.

Fig.2 Mesh around the nose

Boundary Conditions

In terms of the boundary conditions, the figure below explains everything. The air flows into the box at the velocity of U [m/s] and the glider is expected to fly at around 8.0 [m/s] to 10.0 [m/s] so I’ve set U as a parameter and ran the simulation twice. The side walls are defined as slip wall except the one that separates the glider in half which is set as the symmetry plane.

Fig.3 Boundary conditions

Results

In the Fig.4, it is quite clear the pressure on the wings is significantly lower than other surfaces. The pressure above the wings is approximately -20 to -40 [Pa]. This is caused by fast-flowing air above the main wings. According to Bernoulli’s theorem, when two points are at the same height or ignorable, the faster the flow speed is, the lower the pressure becomes.

Fig.4 Pressure distribution

The low pressure above the wings generates lift force and its distribution is illustrated in Fig.5.

Fig.5 Lift distribution

The total lift is 9.99 [N] which is equivalent to 1.02 [kg].

Another thing to mention is the vortex at the wingtip. As I explained, the pressure above the wing gets significantly low. According to the law of physics, fluid tries to flow into the low pressure region so that it’ll be neutralised, but then this creates massive vortex. Not only does a large wake vortex makes the glider unstable, but it also generates drag. In recent years, aircrafts tend to have a small vertical-ish small wing at the end of the wings in order to reduce the size of the wake by separating the high and low pressure regions.

Fig.7 Vortex at wing tip.