Repeating Water Tunnel Studies in Wind Tunnel

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Discussion Overview

The discussion centers on the significance of repeating a water tunnel study in a wind tunnel, exploring whether such repetition yields publishable results or is merely redundant. The scope includes theoretical considerations, experimental techniques, and flow visualization methods.

Discussion Character

  • Debate/contested
  • Experimental/applied
  • Technical explanation

Main Points Raised

  • Some participants argue that if both flows are incompressible and at the same Reynolds number, repeating the study may not hold significance, as it suggests that air behaves similarly to water under those conditions.
  • Others propose that water tunnels may be preferred for achieving specific flow regimes or for ease of flow visualization techniques, such as Particle Image Velocimetry (PIV).
  • One participant notes that flow visualization techniques, like injecting neutrally buoyant dye, are more effective in water tunnels compared to air, where such techniques are limited.
  • Another participant mentions the limitations of smoke visualization techniques in wind tunnels, highlighting that smoke particles are not neutrally buoyant and can settle at lower speeds.
  • There is a suggestion that certain techniques, such as naphthalene sublimation, are only applicable in air flow, indicating a potential limitation of water tunnels for specific applications.
  • Participants discuss the importance of matching conditions to the medium used (water or air) to optimize measurement capabilities.

Areas of Agreement / Disagreement

Participants express differing views on the significance of repeating studies across mediums, with no consensus reached on whether such repetitions are meaningful or merely redundant. The discussion reflects multiple competing perspectives on the advantages and limitations of water and wind tunnels.

Contextual Notes

Participants highlight various assumptions regarding flow conditions, visualization techniques, and the applicability of certain methods in different mediums, but these assumptions remain unresolved.

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Is there any significance in repeating a water tunnel study in a wind tunnel?
If so, would the results be publishable or would it just be considered repetition of a previously published water tunnel study?
 
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There really is no significance if both flows are incompressible and at the same Reynolds number. All it really means is that the air really was incompressible. The main reason you would want to use a water tunnel would be if you need to reach a flow regime that you were simply unable to achieve for one reason or another in air or if you for some reason needed it to be incredibly easy to do PIV or various flow visualization techniques or something along those lines. Otherwise they are essentially interchangeable in most cases where they can both be used.
 
Last edited:
boneh3ad said:
There really is no significance if both flows are incompressible and at the same Reynolds number. All it really means is that the air really was incompressible. The main reason you would want to use a water tunnel would be if you need to reach a flow regime that you were simply unable to achieve for one reason or another in air or if you for some reason needed it to be incredibly easy to do PIV or various flow visualization techniques or something along those lines. Otherwise they are essentially interchangeable in most cases where they can both be used.

Btw, why are flow visualization techniques easier in water tunnels?
 
Do you watch Mythbusters? Have you seen them inject neutrally buoyant dye into the water tunnel and watch it flow over their models? You can't really do that with air. Nothing visible is neutrally buoyant in air like that.
 
boneh3ad said:
Do you watch Mythbusters? Have you seen them inject neutrally buoyant dye into the water tunnel and watch it flow over their models? You can't really do that with air. Nothing visible is neutrally buoyant in air like that.
I don't watch Mythbusters.
Oh I see. I've never tried dye visualization. Have you tried smoke visualization using the smoke-wire technique in Lex Smits' Flow Visualization book? I presume that can only be done in wind tunnels?
 
Sure I've used a smoke wire, which is all well and good, but it isn't truly neutrally buoyant so it doesn't work below a certain speed. The smoke particles will just settle.

Of course on the contrary, things like naphthalene sublimation only work in air flow. I'd imagine that temperature- and pressure-sensitive paints work in water, but I've never seen or heard of it being done.

Really, the reason to use water is if you need the match conditions that water can give you. Same goes for air. If you application would work in either, use the one that gives you the best chance of making the measurements you want.
 

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