Random Wind Tunnel and Smoke Pictures Thread

[freebeard]

I'd always thought this was possible; probably from seeing this years ago and then forgetting the source.

https://en.wikipedia.org/wiki/Schlieren_photography

Colour schlieren image of the thermal plume from a burning candle, disturbed by a breeze from the right.

The new develpment is that it has sprung from the confines of the wind tunnel, due to new image processing capabilities.

Shock waves produced by a T-38 Talon during flight using analog background-oriented schlieren from the Sun's edge

[Cd]

I've seen this used before. I asked about something similar here as well. I noticed that i could literally see the heat waves on my car one day in it's shadow.
The light conditions have to be just right, but it made me hopeful.
It was a very hot day, with the mid-day, to late afternoon sun from behind me.

[freebeard]

I still haven't found one of the B-2 that is awesome, but this showed up on Guns, Oil and Dirt:


Guns, Oil, & Dirt : Photo

They had to get just the right sun angle for the rainbow, and the super-cavitation off the control surfaces is definitely a bonus.

[kach22i]

The Challenge of Standardizing Aerodynamic Testing
May 2015, TruckingInfo.com - Feature
by Jim Park, Equipment Editor
The Challenge of Standardizing Aerodynamic Testing - Article - TruckingInfo.com

In a coast-down test, the test truck is run at a predetermined speed, usually 65 mph, and on a straight, flat section of track, the truck is placed in neutral and allowed to coast down to some predetermined speed. Measurements are taken to determine the relative impact of rolling resistance and mechanical drag (usually constant) and aerodynamic drag (variable with speed). The test requires 20-30 runs and each is measured, compared and averaged along a curve.

[freebeard]

I found the picture I mentioned in Permalink #513.



It was in a catch-all folder so I don't know the provenance.

[kach22i]

Aerodynamics of Heavy Vehicles
An Error Occurred Setting Your User Cookie

We present an overview of the aerodynamics of heavy vehicles, such as tractor-trailers, high-speed trains, and buses. We introduce three-dimensional flow structures around simplified model vehicles and heavy vehicles and discuss the flow-control devices used for drag reduction. Finally, we suggest important unsteady flow structures to investigate for the enhancement of aerodynamic performance and future directions for experimental and numerical approaches.

[freebeard]

If you click on anything, they ask for $32.

[kach22i]

Originally Posted by freebeard

If you click on anything, they ask for $32.

Yea, it's a paper for sale I guess.

Using one or the other's author names in a Google image search shows several of the paper's images - though they are small.

Same guys did the Flying Fish studies for a Wing In Ground Effect (WIG) aircraft.

Haecheon Choi,1,2 Jungil Lee,2,3 and Hyungmin Park1

[BamZipPow]

From the SafeAuto car insurance commercial...

[kach22i]

Time to put bird feathers on your old hatchback apparently - 19 percent reduction in drag?

A bio-inspired device for drag reduction on a three-dimensional model vehicle
Dongri Kim1, Hoon Lee1,3, Wook Yi1,4 and Haecheon Choi1,2
http://iopscience.iop.org/1748-3190/...re/bbaa176ff11

Abstract
In this paper, we introduce a bio-mimetic device for the reduction of the drag force on a three-dimensional model vehicle, the Ahmed body (Ahmed et al 1984 SAE Technical Paper 840300). The device, called automatic moving deflector (AMD), is designed inspired by the movement of secondary feathers on bird's wing suction surface: i.e., secondary feathers pop up when massive separation occurs on bird's wing suction surface at high angles of attack, which increases the lift force at landing. The AMD is applied to the rear slanted surface of the Ahmed body to control the flow separation there. The angle of the slanted surface considered is 25° at which the drag coefficient on the Ahmed body is highest. The wind tunnel experiment is conducted at Re H = 1.0 × 105–3.8 × 105, based on the height of the Ahmed body (H) and the free-stream velocity (U ∞). Several AMDs of different sizes and materials are tested by measuring the drag force on the Ahmed body, and showed drag reductions up to 19%. The velocity and surface-pressure measurements show that AMD starts to pop up when the pressure in the thin gap between the slanted surface and AMD is much larger than that on the upper surface of AMD. We also derive an empirical formula that predicts the critical free-stream velocity at which AMD starts to operate. Finally, it is shown that the drag reduction by AMD is mainly attributed to a pressure recovery on the slanted surface by delaying the flow separation and suppressing the strength of the longitudinal vortices emanating from the lateral edges of the slanted surface.

Yes, another paper available for purchase.