The Coanda Effect in Flow Simulation

Can you take advantage of the Coanda Effect?

 
The Coanda Effect, what is it? Can SOLIDWORKS Flow simulate it? And how can you take advantage of it?

 
The Coanda effect is one of those phenomena of fluids that seem like magic, difficult to wrap your head around and a must see to believe. The effect causes a jet flow to attach itself to a surface and remain attached even when the surface moves away from the initial jet direction, magic right?

 
Knowing the mechanism of the Coanda effect is not the main purpose of this blog, so let’s just skip the mind-numbing explanation. Many of us have already witnessed the Coanda effect before when it’s time to do the dishes without realising. Creating splash patterns when washing a spoon can be quite fun and messy, but if you align the convex part of it with the water stream you’ll feel the spoon getting sucked in, but most importantly, it diverts the flow of water following the spoon curvature, behold the Coanda effect!

 
In order to answer the question, can SOLIDWORKS Flow simulate it? It is appropriate to test it rather than take my word for it. Consider a radial fan as seen below…

Apply some angular velocity to witness the surrounding air flow…

As expected, the fan generates a constant horizontal flow of air. Now, let’s place a surface at the bottom of the fan and see the effect…

Isn’t that just fascinating? By simply adding a surface for the fluid to stick to, the air flow amazingly bends beyond 90 deg, proving that SOLIDWORKS Flow takes this effect into account. If you were to test this yourselves, you’ll find something that is ever more counter intuitive, the higher the flow speed, the more powerful the Coanda effect becomes. 

Now this is all very interesting, but does it have any useful applications?

 
Absolutely, designers have taken advantage of this in different areas for years. From bladeless fans to no tail rotor helicopters, high lift devices on airplanes and even flying saucer prototypes.

 
The summer weather is finally here (sort of) so the next practical example is appropriate. Almost every HVAC system will have some type of ceiling diffuser rather than a simple grill. Why is this? Let’s do a bit of testing.
 

We’ll examine how the following inlet designs affect the overall temperature of a room, a simple grill and a diffuser.

The following temperature results show a cross section of the
room, note that the scale is the same for both result.

Cross section of room for the grill design

Cross section of room for the diffuser design

Just by looking at the previous results you can quickly tell which of the designs you are likely to use. The grill purely directs the air to the floor as expected. The uneven temperatures present throughout the room will inevitably cause discomfort and a cold draft in the middle of the room.

On the other hand, the diffuser spreads the cool air throughout the ceiling due to the Coanda effect. As the air travels further away from the diffuser, it naturally loses velocity and its “stickiness” to the ceiling, thus gradually falling towards the floor. The result is an evenly distributed air pattern across the room, ensuring perfect comfort in every corner by solely exploiting the Coanda effect.

Notice that by merely changing the inlet design we can now enjoy those warm summer days thanks to a more efficient HVAC system, all because of the Coanda effect. Now having a nice cool room will let you think of how to implement and take advantage of this effect in your future designs.

 
Want an even more impressive test of the Coanda effect? Place a lit candle behind a drink can as to block the candle, now blow in front of the can, it’s just magic!