Can a flow created by a fan show an Edge effect when hitting a wall?

[T C]

I am curious to see the velocity and pressure distribution part of this scenario. And, by the way, what's the source of this photo/drawing?

 

[renormalize]

And, by the way, what's the source of this photo/drawing?

Here's the link to the published paper containing the second drawing as part of Fig. 5a:
Two-dimensional steady flow over a semi-circular cylinder: drag coefficient and Nusselt number
If you search this title on Google Scholar you can find a PDF version of the paper.

 

[T C]

Can't see it as I don't have an account. Whatsoever, I am curious about the velocity distribution and pressure distribution diagram of the second photo.

 

[renormalize]

Can't see it as I don't have an account. Whatsoever, I am curious about the velocity distribution and pressure distribution diagram of the second photo.

Did you search the title in Google Scholar for a free PDF as I suggested? What did you find?

 

[256bits]

Ok, I see it, and see that you capitalized "Edge" but not "effect" because that's how it is shown in the video subtitles. Near as I can tell, it's typically called "corner effect" and is about what happens whe a fluid flows around a sharp corner (it accelerates):

Is this your understanding if flow around a house, building, mostly low rise?
The reference given in the post 17 shows that flow around buildings, especially high rise downtown areas, can have complicated air movement patterns.
The upwind velocity U profile need not be that as shown in the figure below, especially if other buildings, or obstacles are in the vicinity. The U shown for the free stream is modelled as either an exponential or as a power function. At ground level, the U velocity is zero, producing the swirl under the stagnation zone. The dead zone is evident on the lee side of the building. ( Note the similarity to an idling car and carbon monoxide poisoning, where the noxious gas can enter the passenger compartment even if the exhaust is exiting at the rear ). ( And snowbank overhang extensions ).

Since the streamlines compress over the building ( and sides as well ), a velocity increase does occur.
It would seem the greatest velocity amplification occurs not at the actual edge but is a function of height and distance from the edge, surpassing U_{roof_height}, and possibly surpassing U_z under particular conditions.

https://www.aivc.org/resource/air-flow-around-buildings
Chapter 14 of Fundamentals 1981 ASHRAE , a copy of which these nice people have provided.
( Can't find my copy of Fundamentals, same year, ( dagnabit )
https://www.aivc.org/resource/air-flow-around-buildings

 

[T C]

Since the streamlines compress over the building ( and sides as well ), a velocity increase does occur.
It would seem the greatest velocity amplification occurs not at the actual edge but is a function of height and distance from the edge, surpassing Uroof_height, and possibly surpassing Uz under particular conditions.

If that's true, then from where the extra energy can come?

 

[256bits]

If that's true, then from where the extra energy can come?

Bernoulli

 

[T C]

That means the fall in temperature following the fall the pressure and the energy released in this way is being converted into kinetic energy, right?

 

[256bits]

That means the fall in temperature following the fall the pressure and the energy released in this way is being converted into kinetic energy, right?

No.
Bernoulli says nothing about a change in temperature.
https://efficientengineer.com/bernoulli/

 

[FactChecker]

It does seem clear from the diagrams @renormalize put in post #27, that the leading corners squeeze the streamlines together. That indicates an increased velocity.

 

[T C]

Bernoulli says nothing about a change in temperature.

Condensation above aircraft wings are a very common phenomenon for a long time i.e. from subsonic to supersonic. Condensation occurs means there is fall in temperature otherwise it's simply not possible.​

 

[FactChecker]

View attachment 369036​

Condensation above aircraft wings are a very common phenomenon for a long time i.e. from subsonic to supersonic. Condensation occurs means there is fall in temperature otherwise it's simply not possible.​

That is a consequence in certain situations of Bernoulli's equation. It is not Bernoulli's equation.

 

[T C]

That is a consequence in certain situations of Bernoulli's equation. It is not Bernoulli's equation.

Whatsoever, it's a proof that temperature fall occurs due to the increase in velocity. I am just curious to know that happened to the energy that has been released due to this phenomenon.

 

[russ_watters]

If that's true, then from where the extra energy can come?

Bernoulli

This answer may be too short/flippant for @T C to have grasped. To expand: Bernoulli's principal/equation is a conservation of energy statement: there is no extra energy. To put a finer point on it, any obstruction will result in a net loss of energy in the flow.

The question here is whether a localized velocity increase can be exploited to provide greater power from a given wind turbine vs the same turbine in freestream. The answer is probably but it is complicated and very situation-specific.

 

[russ_watters]

Whatsoever, it's a proof that temperature fall occurs due to the increase in velocity. I am just curious to know that happened to the energy that has been released due to this phenomenon.

Please look at the standard form of Bernoulli's equation @FactChecker provided and tell us what you see the answer is. You've been looking at related issues to this for years and this question is answered in the first hour of a lecture or chapter on Bernoulli's Principle. It's inexcusable for you to not grasp this by now.

 

[renormalize]

Whatsoever, it's a proof that temperature fall occurs due to the increase in velocity. I am just curious to know that happened to the energy that has been released due to this phenomenon.

The energy "released" by the temperature-fall is exactly balanced by the energy required to increase the flow-velocity. Bernoulli's equation for a compressible fluid (like air) can be written $v^2/2+C_pT=\text{constant}$, where $C_p$ is the specific heat of the fluid. So simple conservation of energy for compressible flow implies higher-velocity $v$ = lower-temperature $T$.

 

[256bits]

Whatsoever, it's a proof that temperature fall occurs due to the increase in velocity. I am just curious to know that happened to the energy that has been released due to this phenomenon.

The Bernouilli equation that one mostly sees, and the one that is presented as an introduction to fluid flow, is of the form in post 42 by @FactChecker. Below about Mach 3, this form can solve the velocities and pressures from one point to another along a streamline quite adequately for a great deal of phenomena.
This form has several assumptions that need explaining
- flow is streamlined
- steady flow in time
- no change in density along a streamline
- viscous effects neglected, ie fluid is considered inviscid, and thus no internal friction
- volume work is considered to be zero, so no work done on or by the fluid
- no change in temperature, so no change in internal energy of the fluid

A general energy equation of the form from the first law of thermodynamics.
Q + W = ΔU + ΔPE + ΔKE + ΔPV

Since Q = 0, W = 0, ΔU = 0, we are left a constant energy from point 1 to 2 along a streamline in terms of the changes in only KE, PE, and PV of the fluid.

 

[FactChecker]

The question here is whether a localized velocity increase can be exploited to provide greater power from a given wind turbine vs the same turbine in freestream. The answer is probably but it is complicated and very situation-specific.

Good point. I think that is the unexpressed question of the OP. The diagrams that @renormalize included in post #27 seems to indicate that the velocity can be higher than the freestream velocity. The streamlines appear closer together at the leading corners of the obstruction than they were in the freestream.

 

[renormalize]

The diagrams that @renormalize included in post #27 seems to indicate that the velocity can be higher than the freestream velocity. The streamlines appear closer together at the leading corners of the obstruction than they were in the freestream.

I don't think that's the right interpretation. The flow-speed plots in fig. 6 of my post #26 show lower speeds (blue) everywhere around the building compared to the higher incoming freestream speed (yellow/green). But what you can say is this: if you have a turbine of finite aperture-width $w$, placing it at the corners is better because it will capture a higher average flow speed (since the streamlines are more closely spaced there), compared to putting it nearer the stagnation point on the front wall. But in neither location will those average speeds be as high as the freestream speed. Obstacles always diminish nearby flow speeds to below that of the unperturbed freestream.

 

[FactChecker]

I don't think that's the right interpretation. The flow-speed plots in fig. 6 of my post #26 show lower speeds (blue) everywhere around the building compared to the higher incoming freestream speed (yellow/green).

Sorry. I stand corrected. I was thinking about incompressible fluid flow. Thanks.