Dear Fellows of the Basement Science Research Consortium,
For those new to the field, it is an important lesson to learn that the longer and more complicated the organization name, the more prestigious and talented the group. Therefore, we are part of a very important research group!
Our next task is to build the bell mouth. An overview of this was explained here a little earlier. I was trying to think of a good way to construct this as I was wandering though Home Depot. First, I browsed the ducting aisle with no luck, but came across aluminum flashing in the insulation section. I thought this would do very well. It is in long sheets, very bendable, and yet stiff. This will serve as the surface of the bell mouth, but we need to build a structure to hold it in place. It does not need to be a solid surface, but just a rib structure to attach the flashing. So, my idea was to use correctly shaped rips attached to the test section with gusset. The flashing could then be cut and the strips screwed to these ribs. Here is a picture previewing construction so you can get an idea of what was in my head:
With this idea we need to determine the shape of the bell mouth. Well, the secret is out because of the picture, but here was my process. The goal is to have as provide a smooth transition for air from the room into the test section. My first thought was a cubic polynomial which is just like a big nozzle. This is because I had just finished designing some nozzle for university research. After trying to draw some possible shapes, my ideas moved to a bell shape which made more sense, hence why I call it a bell mouth. The cubic nozzle provides a transition from its larger diameter to its smaller, while a bell mouth provides a transition from a theoretically infinite diameter to the test section. This is better. This design also alines with my experience in fluid mechanics lab. Here I performed tests with a water tunnel, like a wind tunnel, which used a bell mouth shape to funnel water from a reservoir. This is comparable to our situation, where the open basement is a reservoir and it moves into the wind tunnel.
So we have our shape but we need to choose the size. I want it to be big, but not bigger than I can manage constructing. The reason bigger is better is so the flow can more steadily, not abruptly, increase its speed. This promotes less turbulence in the test section. I decided, somewhat arbitrarily, to make the entrance twice the size as the test section. Since my test section is not square, the right and left will be a little larger than the top and bottom.
Here is the design overview of the bell mouth using my dimensions:
Okay, we have the design figured out and purchased the aluminum flashing, so its time to build. Its always exciting for me to start building because I get antsy if I spend a lot of time designing. It feels like I am not getting anything done, but in the end it saves so much time. It also feels really good to cut things.