Solar "Hump" for aerodynamics for Class A RV

[eXodus]

I don't know much about your specific vehicle but I guess I'd want to be sure any such additions are not going to adversely affect the engine cooling system.

from what I read on the Ecomodders discussion board - an airdam should reduce the pressure underneath the vehicle and speed it up - both things are beneficial for cooling. Since you got a high pressure air building up in front of the radiator.

Cool. A lowly 1980s ANU physics/maths degree for me.

Electrical Engineer from 2008 you guys got an experience headstart.

Suppose you install an 82" wide wedge with the leading edge having a zero height forward. Now, extend the length of the back facing edge towards the back at a rise of 2" per 40".

If that is a zero height leading edge, then does if follow that the trailing height can be ignored? At what point do the edges matter?

mechanics / aero is not my strong area yet. I wire up stuff and research how to power buildings on Mars but can not really guess what wind does to a panel.

The tallest the panel edge will be - is 5 inches - nowhere close how other people are mounting there panels.

 

[Cajunwolf]

If you gork physics and math, you're pretty much an engineer except for the engineering standards and best practices; engineering is all about math, and if you can't do the math, you can't be an engineer. I loved physics! I've been out of engineering and into retirement for some time now. I left the professional field of engineering early, too restrictive. I've done many things since, some I hated, some I loved, but I learned valuable lessons on life from each.

 

[wattmatters]

mechanics / aero is not my strong area yet.

Fluid dynamics is weird stuff and one the more difficult of the sciences to grasp. I guess there's a reason why the $1M millennium prize is still unclaimed.
https://en.wikipedia.org/wiki/Navier–Stokes_existence_and_smoothness

The good thing is we don't actually need to have anything like that level of understanding to do most of the practical stuff.

Some quotes to give some idea of the challenge faced by those seeking to formulate physical solutions although forgive me for not verifying their attributions:

`Turbulence is the most important unsolved problem of classical physics.'
- Richard Feynman -


`I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic.'
- Horace Lamb -


`Big whorls have little whorls, which feed on their velocity, And little whorls have lesser whorls, and so on to viscosity.'
- Lewis Richardson -

 

[curiouscarbon]

tossing one more option for free CFD http://flowsquare.com/

2d and 3d domain, can draw the RV shape in ms paint as viewed from side, and load image up with sideways wind and watch particles fly etc.

can outline in ms paint and load it up ??
draw flashing and panel etc, maybe it could show turbulence..

Lesson 2.2 — ic.bmp | Flowsquare

flowsquare.com

 

[curiouscarbon]

View attachment 75688

made a really crude side view image on phone for sim


if have time later today, ill try to load it up in squarespace with a rightward wind and see what happens ?

 

[curiouscarbon]

masked the image to facilitate usage in flowsquare or other CFD software..

original:

with drawn panel in first post

?

 

[curiouscarbon]

Fluid dynamics is weird stuff and one the more difficult of the sciences to grasp. I guess there's a reason why the $1M millennium prize is still unclaimed.
https://en.wikipedia.org/wiki/Navier–Stokes_existence_and_smoothness

The good thing is we don't actually need to have anything like that level of understanding to do most of the practical stuff.

Some quotes to give some idea of the challenge faced by those seeking to formulate physical solutions although forgive me for not verifying their attributions:

chaos CANNOT be predicted!!

unless??

 

[curiouscarbon]

Shadertoy is a website.. (that i like a lot!) for visualizations and simulations on graphics card rendered in Browser.

people post Code and it's Run on Graphics Card for Supercompute on Everyday Computers

it uses the Graphics Card of the computer to render SuperComputing Visualization in Browser.

these links are to various navier-stokes related simulations that have been published for free on shadertoy to be viewed for free

each one renders fluid simulations in real time on the browser (firefox sometime not work, chrome works, safari sometime not work)

Shadertoy

www.shadertoy.com

Shadertoy

www.shadertoy.com

Shadertoy

www.shadertoy.com

Shadertoy

www.shadertoy.com

Shadertoy

www.shadertoy.com

example screenshot from browser:



(works best in chrome because Shadertoy uses Graphics Card heavily, and that browser has best GPU support afaik..)

 

[wattmatters]

chaos CANNOT be predicted!!

Depends what you mean by predicted.

e.g. weather systems are chaotic but weather can be predicted in a probability sense, and they also operate within certain climatic system boundaries.

But know what you mean. Something as simple as the 3-body problem is astonishingly difficult.

 

[curiouscarbon]

Depends what you mean by predicted.

e.g. weather systems are chaotic but weather can be predicted in a probability sense, and they also operate within certain climatic system boundaries.

But know what you mean. Something as simple as the 3-body problem is astonishingly difficult.

well said..

ambiguous language on my part

statistics of patterns may be expected, while specific weather patterns are mystery.. ?

Shadertoy

www.shadertoy.com

Shadertoy

www.shadertoy.com

Three-body problem - Wikipedia

en.wikipedia.org

The Three-Body Problem (novel) - Wikipedia

en.wikipedia.org

 

[curiouscarbon]

excited to witness fuel consumption metrics over next year!

 

[curiouscarbon]

Fluid dynamics is weird stuff and one the more difficult of the sciences to grasp. I guess there's a reason why the $1M millennium prize is still unclaimed.
https://en.wikipedia.org/wiki/Navier–Stokes_existence_and_smoothness

The good thing is we don't actually need to have anything like that level of understanding to do most of the practical stuff.

Some quotes to give some idea of the challenge faced by those seeking to formulate physical solutions although forgive me for not verifying their attributions:

`Turbulence is the most important unsolved problem of classical physics.'
- Richard Feynman -

playlist of uncertainty, simulation, hopefully low turbulence!

*been spamming this thread a lot, still believe small fuel optimization by PV install worthy!

 

[eXodus]

masked the image to facilitate usage in flowsquare or other CFD software..

original:
View attachment 79170
with drawn panel in first post
View attachment 79171
?

thanks for doing that! How do I plug that in a Fluid dynamic tool?

I've looked at shader websites and Flowsquare - but no clue where to start

 

[curiouscarbon]

thanks for doing that! How do I plug that in a Fluid dynamic tool?

I've looked at shader websites and Flowsquare - but no clue where to start

its been a while and frankly forgot how to work Flowsquare. when i can load it up will share steps to get it going or just share the project file. its free, but like someone said they get ya with the learning curve?

basically it takes three main files together in a folder as input. 1) text file describing basics like simulation resolution 2) BMP image file "ic" initial conditions and 3) BMP image file "bc" boundary conditions (any input image must be BMP format)

basically each color in the input image is a code for a type of object, so to speak.. where Black (r=0,g=0,b=0) by default is a stationary wall, Blue (0,0,255) is an inflow boundary.

so like draw some pure blue on the left side of bc.bmp and that will be simulated as incoming/oncoming air "during forward driving". and then anything pure black will be simulated as an obstruction and flow will go around it

mainly bc and config.txt input are most important

again, i oopsie and forgot how to get it working, will post steps if i can get it going?

 

[justgary]

Your posts intrigued me, so I have two cases running right now; one with panels and one without. Both are at 100 kM/Hr (62 MPH). They are going to take a while, but I will post results here when they finish. The first look shows me that I am no longer worried about excessive pressure on the panels, and the size and shape of the front of the RV suggests that nothing on the roof really has much consequence on mileage.

 

[justgary]

Here are my input files in case you want to run it as well. Change either of the .bmp files to "bc.bmp" to run that case.

 

[AndyRonLI]

Okayyy, Been doing CFD for 38 years. Be Careful. Even if you use the 3D version of this tool, if you dont really understand the inherent fluid dynamics you can get in trouble. That said, thats a clever little tool. You can certainly use it to evaluate a fairing, even a 2D analysis on the centerline would likely be helpful. Just remember that you want Computational Fluid Dynamics, not Colorful Fluid Dynamics.

 

[eXodus]

Your posts intrigued me, so I have two cases running right now; one with panels and one without. Both are at 100 kM/Hr (62 MPH). They are going to take a while, but I will post results here when they finish. The first look shows me that I am no longer worried about excessive pressure on the panels, and the size and shape of the front of the RV suggests that nothing on the roof really has much consequence on mileage.

Can you post some screenshots? For whatever reason the flow program is only showing large pixels on my computer and I can not see the shape of the RV.

If there is no impact to what's on the roof that would be OK. Just don't want to make it worse . I'm hopping for better but hey I will take no impact

 

[curiouscarbon]

Okayyy, Been doing CFD for 38 years. Be Careful. Even if you use the 3D version of this tool, if you dont really understand the inherent fluid dynamics you can get in trouble. That said, thats a clever little tool. You can certainly use it to evaluate a fairing, even a 2D analysis on the centerline would likely be helpful. Just remember that you want Computational Fluid Dynamics, not Colorful Fluid Dynamics.

absolutely agree! flowsquare is a free toy

please not use only flowsquare alone to inform structural design!

mainly hoping it can be used for *rough* design brainstorming, with analysis of simulation state to be taken with a teaspoon of salt grains ?

if seriously evaluating forces on a structure, use the real stuff that has traceability!

all that said, flowsquare does seem to have pretty solid technical foundation from what i can gather.

thank you!

 

[justgary]

Some disclaimers: Like @AndyRonLI and @curiouscarbon both said, this should be taken for its entertainment value only. You are getting free advice from your "best internet friend" who is neither an aerodynamic engineer nor a structural engineer. Do not mistake any of this for actual engineering. These diagrams show airspeed only, and not pressure.

@eXodus, if you don't see these kinds of results, perhaps you didn't rename one of the .bmp files as "bc.bmp".

With that said, I still hesitate showing you the first results because I think it has a problem.

RV_Nopanels at 100KPH (62.2 MPH):


RV_Panels at 100KPH (62.2 MPH):


The problem? It looks to me like the flow gets very distorted when it hits the top of the calculation frame, causing it to build pressure and break free. In other words, I don't think the calculation area is large enough to keep it from interfering with the answer. I am running another one now with a 400x200 calculation space, but it won't be done for hours.