Travel Trailer Aero mods?

[seuadr]

Originally Posted by aerohead

this goes back a few generations, but illustrates some of the challenge to streamlining an ICE underbody, compared to a BEV underbody.

fortunately, for the travel trailer there is not really any driveline to work around as everything is mostly tucked up inside the frame rails already - but the material that they use is very flexible and it is meant to cover the bottom, not streamline - for instance:



it seems like there is an opportunity to round out those flats (this is very similar to my trailer)

Originally Posted by aerohead

the original box-cavity, by Continuum Dynamics, financed with a Defense Advanced Research Projects Agency (DARPA ) / Small Business Administration' ( SBA ) innovation and research grant.
You may notice how 'shallow' the vortices are, captured along the spans of the four longitudinal panels.

Am i understnading this correctly - instead of a boat tail i could look at a stepped box (like in the picture)
for similar results? that is attractive because it would keep storage open for me, as well as likely be something
i could fold down when not in use.

Originally Posted by aerohead

Introducing a more radical change in initial cross-section violates adverse pressure gradient boundary-layer rules

Mmmhhh Mhhh - I definitely recognize some of those words.

I have no idea what that sentence means, but it sounds important?

i'm looking in to an inflatable section between vehicle and trailer - that sound simple to test and probably rather inexpensive

while googling it, i found a patent for a "Boat trailer with inflatable bladder" and got excited, but
turns out it is for keeping it from sinking - Borrrrinnnnggg (not really, i thought it was pretty cool)



now, would i need to have something to keep it inflated like those flailing car lot guys, or, do you think it might be possible to rig up an intake so that my driving inflates it appropriately?

I also still have diffusers to look in to - i've run across the concept in regards to a vehicle solo - and, actually in the act of working on replacing an evap canister vac valve found that the bottom of the durango actually already has a lot of pan in place (presumably to protect components) so i'm not sure if a diffuser in addition would make sense? thoughts?

Would i also be putting a diffuser on the trailer in the front?

Thanks again for your time and effort!

Jared

[seuadr]

Originally Posted by freebeard

I posted this picture:

i completely missed this reply, i apologize. i think the rounding would happen with the front... fairing?

here is my running list of potential ideas:

[freebeard]

completely missed this reply, i apologize. i think the rounding would happen with the front... fairing?

The intent is to add radius to the edge, without having to cut into the original structure.

[seuadr]

Originally Posted by freebeard

The intent is to add radius to the edge, without having to cut into the original structure.

i really wish that i had any kind of photo editing skills at all lol.

so are you saying that i might wanna consider adding a rounded bumper to the leading edges instead of a "bubble" ?

i bet i could fab up something temporary to represent that for testing from dense foam pipe insulation or something. i'd have to figure out the radius but if that gave even modest improvements that'd be real easy to make a solid modification and i think just about anything you make it out of would be pretty light an inexpensive.

[freebeard]

i really wish that i had any kind of photo editing skills at all lol.

I [occasionally] combine Photshop/GIMP, tracing off the screen, photograph the sketch, [rinse and repeat].



Minimal radius is 4% of the gross width, IOW 4" in 8ft, the middle part isn't doing anything. Note the Vortex Traps here in the lower right:



Spoils cross-winds.

[seuadr]

Originally Posted by freebeard

I [occasionally] combine Photshop/GIMP, tracing off the screen, photograph the sketch, [rinse and repeat].

I can't believe that it didn't even occur to me to try out using my terrible real life drawing skills to supplement my terrible computer drawing skills

in all seriousness though, that is a great idea, and i think would make my effort a lot easier - cause i'm a very visual person so being able to kinda stick what i'm thinking on paper and then say "like this?" is of value, even if it leads to a "no - not like that"

[aerohead]

Yep!
Since the RV is typically wider than the TV, the 'hard' leading edges on both sides are just shredding the flow. The flow will reattach downstream, but you're constantly paying for this region of turbulence which travels along with you.
An inflatable envelope, deployed while accelerating up the cruise speed could essentially seal the entire gap between TV and RV. You're no longer appreciably 'turning' while on the open road, so closing off the whole gap isn't an issue.
A look at what these gaps will do to wing sections will bring tears to your eyes ( Figure 134, page 228, THEORY OF WING SECTIONS, Abbott & Von Doenhoff ).
The inflation fan electrical current can be automatically disenabled below 45-mph, in anticipation of 'urban warfare'.

[aerohead]

Unfortunately, we don't have any back-to-back performance comparisons between a box-cavity and boat-tail of equal length.
These nested backwards facing steps would be 'way out ahead of nothing'.
Since we never see them on nuclear submarines, airships, commercial airliners, bullet trains, etc., there's an implication of inferior performance compared to a proper tail.
Unlike a Class-8 tractor-trailer van, loading and unloading from the rear of an RV is a non-event.
If you need to go up and down the ladder, any tail could be hinged at one side, and swung away if needed at the campsite.
If your time and finances are liberal, you may want to start with a 'low-ball' project like a cavity, with no expectation of 'terrific' results.
If you only want to build something 'once', and then I advocate for the most complex boat-tail you have the courage of taking on.
These projects can constitute up to 800-man-hours if you want something with an OEM look to it.

[aerohead]

Originally Posted by seuadr

i completely missed this reply, i apologize. i think the rounding would happen with the front... fairing?

here is my running list of potential ideas:

Basically, you want to imagine an aerodynamic singularity. Not a tow vehicle and a trailer, but a single 'system', without kinks and mutilations.
Your tow vehicle will do the penetration, as with Lanchester's ( Entry ) 'head' and 'shoulder', and the gap-filler and trailer play the role of ( Run ) 'buttock' and 'tail'. Gaps are your enemy.
The flow remains attached over the entire length of the TV, then seamlessly transitions onto the gap-filler, then the trailer.
Whatever rear modification exists, it is there to allow the displaced streamlines to gently re-converge, back where they were before you ever came along.
Allowing for ground clearance, the belly and side of the RV should pick up on what the rear of the TV has, and just project that rearwards.
All the belly area should be as smooth as possible.
Rear wheel skirts are an insurance policy for clean onset flow to the tail.
There should not be a forwards 'diffuser,' just make the nose of the gap-filler level with the tail of the TV.
A rear diffuser on the TV would be great, but it won't do a thing for you without a complete belly pan ahead of it ( this isn't a race car on track day )
The roof should be 'naked', not a cemetery full of 'headstones'.
Let the Bowlus line of trailers and the new 'naked' Airstream be your guide.
If you choose a box-cavity, imagine a proper boat-tail, then position the rear of each step where they would intersect a 4-foot chopped truncation of the tail. It's going to contain the vortices within a region of no greater adverse pressure gradient than a proper tail would generate ( if you've got $ Millions, then head for Palo Alto California and blow it all at NASA Ames ).

[aerohead]

Originally Posted by seuadr

i really wish that i had any kind of photo editing skills at all lol.

so are you saying that i might wanna consider adding a rounded bumper to the leading edges instead of a "bubble" ?

i bet i could fab up something temporary to represent that for testing from dense foam pipe insulation or something. i'd have to figure out the radius but if that gave even modest improvements that'd be real easy to make a solid modification and i think just about anything you make it out of would be pretty light an inexpensive.

For commercial vehicles, and wind-averaged flow, the 'bulbous' nose has been found superior to all other shapes in subsonic flow.
The greater the radius ( up to, and including that of a semicircle ) the smaller the pressure spikes, and better turbulent boundary layer health when it comes to aft-body mods. Another insurance policy.