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Old 04-23-2020, 01:29 AM   #1 (permalink)
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More data on smooth wheel covers effectiveness

A couple key findings on smooth wheel covers of interest to this forum, from:

Sofie Koitrand, Adrian Gaylard, and Gianluca Orso Fiet, "An Investigation of Wheel Aerodynamic Effects for a Saloon Car" - Conference Paper - September 2015
Conference: Progress in Vehicle Aerodynamics and Thermal Management: Proceedings of the 10th FKFS-Conference, At Stuttgart, Germany

The PDF is currently available online for free. Thanks to the authors and their professional org for that. I will share just a small portion of their findings, but there is more. Go get their paper and read it if you want more.

In another thread, a few forum members have been discussing the effectiveness of several aeromods for wheels. This study uses a wind tunnel (with 5 belts) and CFD to study these different wheel designs:



The conclusion was that the fully blanked, smooth cover wheel saw the greatest reduction in drag:



That graph presents a combination of the wind tunnel & CFD data. In the wind tunnel alone, the fully blanked wheel saw a delta of -0.013 Cd, the 85mm annular blanked wheel -0.009, and the 430mm center-blanked ("Tesla" style) wheel saw a -0.003 Cd delta.

Their conclusion is that in this test fully smooth covered or blanked wheels produced the greatest Cd benefit over baseline, whether measured in a wind tunnel or using CFD. This is a different conclusion than some other recent studies.

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Old 04-23-2020, 02:28 AM   #2 (permalink)
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Good find. Note that the graph you have shown simply displays the difference in CFD prediction vs wind tunnel results (ie the error) - not the actual changes in drag.

Versus the standard rim (wind tunnel results):
  • fully blanked - Cd change of -0.013
  • 85mm annular outer ring - Cd change of -0.009

So the Jaguar results are different to the Tesla results (where fully covered wheels increased drag), which in turn are different to the SAE 2011-01-0165 results (where ventilated front and fully covered rear wheels gave the best result).

As I wrote in the other thread:

To make it clear, based on the research I have cited in the book, I am not saying that fully covered wheels are bad. What I am saying is that fully-covered wheels aren't always best.

I am guessing it's highly dependent on the car to which the wheels are fitted.

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Old 04-23-2020, 02:46 AM   #3 (permalink)
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Quote:
Originally Posted by JulianEdgar View Post
Versus the standard rim (wind tunnel results):
  • fully blanked - Cd change of -0.013
  • 85mm annular outer ring - Cd change of -0.012
I already noted these data points in the OP. But you get the number wrong here. The wind tunnel results for the 85mm ring were -0.009. You are mistakenly quoting the CFD number of -0.012. It's on p.248, table 18.3.
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Old 04-23-2020, 02:57 AM   #4 (permalink)
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On a car, at 65mph that could be up to a 1hp reduction in power requirement to maintain speed.
Not bad.
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Old 04-23-2020, 03:01 AM   #5 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
On a car, at 65mph that could be up to a 1hp reduction in power requirement to maintain speed.
Not bad.
Right?! Their testing speed was 140 kph, I think. But still. I'd like to think my wheel covers gimme back an HP at 65 mph cruising.
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Old 04-23-2020, 03:07 AM   #6 (permalink)
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At autobahn speed you are definitely saving at least 1hp.
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Old 04-23-2020, 03:41 AM   #7 (permalink)
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Quote:
Originally Posted by California98Civic View Post
I already noted these data points in the OP. But you get the number wrong here. The wind tunnel results for the 85mm ring were -0.009. You are mistakenly quoting the CFD number of -0.012. It's on p.248, table 18.3.
You are right! I have edited my post.
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Old 04-24-2020, 01:56 AM   #8 (permalink)
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Of course, absent from this discussion is the need for brake cooling, which from a manufacturer's perspective is probably at least as important as aerodynamic efficiency. (And I think it is pretty important too!)

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Old 04-24-2020, 03:22 AM   #9 (permalink)
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Citation needed?

www.researchgate.net: An Investigation of Wheel Aerodynamic Effects
for a Saloon Car


I remember the name Adrian Gaylard from discussions a few years back.
Quote:
Originally Posted by DDG
Adrian Gaylard - Technical Specialist - Computational ...
https://www.linkedin.com/in/apgaylard
Progress in Vehicle Aerodynamics and Thermal Management, 9th FKFS-Conference October 1, 2013 Realistic turbulent flow conditions, typical for highway driving, can have a significant effect on ...
LinkedIn wants an email address. No thanks. U of Georgia and Coventry University were also notable. A lot of the materials disappeared, I had captured a few Powerpoint slides like this (added to my album in 2013(!)):



I did a search and surfaced a few other interesting articles at ReasearchGate:

www.researchgate.net/publication: Automotive Aerodynamics Special Issue Surface contamination of cars: a review

https://www.researchgate.net: The importance of unsteady aerodynamics to road vehicle dynamics

There are links to other articles at the bottom of some of those. Examples:
Quote:
Optimization of the aerodynamic drag reduction of a passenger hatchback car
July 2018 Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering

Proposal of an Aerodynamic Concept for Automotive Drag Reduction
November 2014

Drag Reduction Devices
Adrian Gaylard Martin Passmore Max Varney[...]Y.A. Irving Brown
I [think I] remember this one:
www.researchgate.net: The Effect of Base Bleed and Rear Cavities on the Drag of an SUV

I wonder whether they really went away and are back, or what?
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Old 04-24-2020, 03:30 AM   #10 (permalink)
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Yes, Adrian is a lovely guy.

He gave extraordinarily detailed feedback on each of the book chapters I sent him.

Through him, I also got the Jaguar XE for a week to aero test, and then I was able to compare the on-the-road test results with his 'official' Jaguar CFD - and have him comment on the differences!

Really down-to-earth and quite frank in his feedback.

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