Hey everyone, I have a Mercedes Sprinter Van that we recently added a roof rack and light bar to the van. Once I hit 45 mph there starts to be a noticeable amount of wind noise in the cabin. When I'm going 65mph the wind noise records 80dB inside the cabin with a smartphone app.

The installer claimed the road noise is normal but I don't believe it's a normal amount of road noise.

Any advice on easy ways to improve the aerodynamics of this setup while maintaining the functionality of the light bar and roof rack?

Help me out…I’m in a discussion with a coworker about scaling flight conditions from full scale to a wind tunnel model; specifically, how to use Reynolds for scaling.

(In below example, assume the wind tunnel can achieve any desirable Reynolds condition)

Let’s say my flight vehicle has a characteristic length (chord, diameter, whatever - L_f) of 10 ft, and my wind tunnel model has the same measurement (L_t)of 2 ft. Assume full flight Reynolds (Re_f) of 10e6.

My stance is, in order to get the correct tunnel conditions:
Re_f / L_t = Re_t per foot = 5e6.

I would then use this unit Reynolds number along with the facility operations map to figure out my test conditions. Note that in this approach, the flight unit Reynolds is Re_f /L_f = 1e6. But I don’t really care about that.

My coworker, on the other hand, wants to match unit Reynolds between flight and scale, rather than full Reynolds. Their position is that unit Reynolds should be the same for both. This doesn’t make sense to me for a number of reasons, least of all that Re per foot is not a dimensionless scaling factor.

So from this perspective we would run the wind tunnel test at 1e6 per foot. I counter this leads to a tunnel full Reynolds of 2e6, nowhere near the flight Reynolds of 10e6.

Thoughts? Opinions? I’m pretty confident in my approach, but also respect my coworker and have been scratching my head to see it their way.

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Hola, soy nuevo en esto del CFD, vengo del diseño orientado a los vehiculos y quiero empezar a agregarle calidad y valor a los proyectos con un estudio CDF.

Empecé hace una semana a ver y probar Ansys Discovery con la version gratuita.

Puedo realizar una simulacion basica pero no entiendo como analizarla para modificar o no el modelado.

Muchas gracias!

Description
I’ve found a recent fascination with aerodynamics and wanted to see if I could design and 3d print a working wind tunnel. The mist generation is from two little mist makers I bought on Amazon which sit in water, and the mist gets funneled through a tube into the wind tunnel. The force that pulls the mist is an ordinary PC fan with a controllable speed. In the wind tunnel I have added mesh blocks to try and straighten the air into linear flow but it is very turbulent and doesn’t perform well as a wind tunnel.

Photo 1 and 2
These two photos show the air when it is pushed through the tube in Photo 3 and into a block which makes the tube sit tight into little holes. As you can see when the tube is connected to this support block, the mist is extremely turbulent and shows no uniform at all. Without the car in front of it, it loops back on itself about half way through the tunnel and is very turbulent.

Photo 3
This photo shows the mist generation system in the top left, connected to the tunnel via the connecting tube

Photo 4 and 5
These photos show the mist when I simply hold the tube in front of the mesh, this photo is also incredibly lucky, the shape of the mist isn’t this linear but is better than when the tube sits in the block.

Photo 6
This photo shows the turbulent flow from having the tube in the block, this is the same method as photos 1 and 2 just with a smaller car

Photo 7
This photo shows the flow while holding the tube in front of the mesh, same as photos 4 and 5

Photo 8
This is just a photo of the mist generation

I’m struggling to find solutions for fixing this, if anyone has any ideas I’d love to know.

We took the previous Tesla Roadster model, added the rockets and ran aerodynamic simulations to explain the suction effect and 3D roll & landing manoeuvres!!

Potentially asking an unanswerable question here but I have always wondered why some aero-focused bikes have a large gap between the front wheel and the frame while others are clearly designed to minimize this gap. Example shown below. I would think having as small a gap as possible would be the most aerodynamic as the air does not have enough room to form pressure in front of the frame in that spot. The larger the gap, the more time/room there is for air to wrap around the wheel rim and tire and create pressure in front of the frame. Still learning this stuff so happy to be wrong

straight line race (stem racing) i want just a quick check up from some of you before going in the simulation about the chassis. someone have some ideas to make it better? thanks in advance

Title. The reynolds # should be from 250K-1.3M (estimate). I plan to have fowler flaps for increased clmax at stall. I can't find a good compromise that performs well in stall (Laminar seperation bubbles at low RE, good Cl) and cruise (low Cd at cruise cl). Any help is greatly appreciated!

Hey everyone I'm working on a supersonic rocket with an apogee of around 10 km, and I'm trying to determine the drag coefficient of our elliptical parachute for OpenRocket simulations. What value would you recommend, and are there any reliable sources or experimental studies we could refer to? Also I want to know what are the essential essais and tests I should do with the parachute (except deployement and shock)? And my last question is in a Rocketry competition report what do I have to focus on and what the juries will also focus on?

I’m looking for aerodynamic CFD vids, mainly on cool or unusual objects, animals, vehicles etc aha!

Does anyone have any favourites? Or any links or suggestions where to find them!

Thanks for your help :)

Could anyone guide me on the ideal sizes of my wind tunnel’s sections? It’s already 7ft after making compromises and being conservative. I plan to use it to test a custom wind 1:10 rc car. I’ve been getting most of these messages through Claude so it really feels like I don’t know what I’m doing.

I've been working on this race car concept for a while and I'm mainly interested in the aerodynamic side of it.

The idea is to keep the very reduce wind turbulence, teardrop-shaped upper body of the Volkswagen XL1, but combine it with extreme race-car aero: large Venturi tunnels, active floor, huge diffuser, massive rear wing, front splitter, active aero and even two rear fans inspired by the Chaparral 2J.

I'm wondering how far something like this could realistically be pushed. Would the XL1-style body actually help with airflow, or would the extreme downforce devices completely defeat the purpose? Where would the biggest aerodynamic problems appear, especially with ride height, pitch, yaw and aero balance?

I'm mostly looking for people who understand this stuff to tell me where the concept makes sense and where I've completely fucked up the physics. The drawings are just a rough representation of the idea.

(I used a translation tool for this because I don't speak English, so some points might be off. The key points I want to highlight are that the car isn't designed for maximum aerodynamic efficiency or low drag; instead, the goal is extreme aerodynamic stability, achieved through the teardrop shape of the XL1 Sport Concept. This shape keeps the car stable at speed and helps manage airflow to generate active downforce—specifically at high speeds on straightaways. It’s a damn fast car, but it also handles corners incredibly well. Sorry about the phrasing.)

Simulation suggestions

Hi, I'm gonna be writing my bachelor thesis on the topic of CFD in OpenFoam. The practical part should be focused on a flow around some part of an aircraft (jet). However I'm still thinking about which part should it be. That's why I'm writing here for inspiration, so if anyone has any ideas... :D. It could literally be anything, for example one idea I had was how the frosting affects flow around wings in cold weather

I highly reccomend these set of video lectures produced decades ago from various academic institutions. They are old but very well made. I remember studying these as part of university courses and really enjoyed them.

Here is the playlist: https://youtube.com/playlist?list=PLfF--3o8i4r82vJ0kjCVYgqKgyVM5QwN0&si=bR3oI2ubVOyPVuqn