Drag figures for Kamm cut teardrops at various lengths?
Do you know of some drag (and maybe lift) tables for teardrop shapes cut at various lengths, Kamm style?
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http://ecomodder.com/forum/member-pi...0-previous.gifI thought I remember something like that, only it looked like the Template. I searched, I searched, but I didn't find it:(
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cut
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I've been working with it slowly over a number of years now,converting the tables into smaller bite size visuals. You'll see Kamm's actual wind tunnel model configurations with accompanying Cd for each 'slice.' If you're in a hurry,get a local librarian to locate the nearest library which has a copy.You probably won't be able to do a inter-library loan,but it would be worth a trip. |
Drag of recessed truncated teardrop
Great to see the table on drag vs truncated lengths of teardrops as well as the graph on same subject -- I am interested in what is known as a "Camm Back" configuration as contrasted to the "Kammback" chopped off rear or downstream end. It appears that this Camm Back refers to a recessed rear face with outside thin or even knife edge shell extending out beyond this recessed face. Examples including the 1960 era Triumph TR6 with a sharp edge protuding further back beyond the vertical rear face of trunk. From what I have found, apparently this helps move the turbulent fluid back away from the truncated tail and reduces drag even further -- Does anyone know anything about this configuration and related data?? I am also interested in application of the truncated tail drag data as applied to water instead of air -- Does same data hold true for this much denser fluid or are some limits or adjustments necessary??
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"box cavity"
http://ecomodder.com/forum/member-fr...31-1-26-08.png Colani: http://ecomodder.com/forum/member-fr...ni-desktop.jpg Quote:
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Kamm's drag figures
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The models tested with K-form architecture represented five different lengths as opposed to Lay's four,adding an intermediate length between Lay's #3 and #4 position. *The model terminated at 77.3% of the Aerodynamic Streamlining Template,with the rear contour terminating at 27-degrees. *Length #1 was 37.5% AST.and measured Cd 0.25 with zero edge rounding,and zero plan taper. *Length #2 was 45.5% AST and measured Cd 0.24 under the same conditions. *Length #3 was 53% AST and measured Cd 0.24. *Length #4 was 67.5% AST and measured Cd 0.22. *Length #5 ,77.3% and Cd 0.21. Here is the table http://i1271.photobucket.com/albums/.../2-289-141.jpg ------------------------------------------------------------------------- *With Buchheim et al.' body side camber the full-tail Cd falls from 0,21,to 0.186. *With Lay's 0.14% body width radius edge rounding the Cd falls from 0.186,to 0.151. *With the full tail plan taper escalation the Cd drops from 0.151,to O.12. I don't have any facility to analyze the intermediate positions but I did a breakdown at the AST Part-C thread. *Essentially,the body drag varies as with the fuselage truncation,with the wheel/tire drag super-imposed upon that drag to reach the total. *The fuselage drag doubles in ground reflection and it's half-body carries the entire drag of both 'above' and 'below' ground half-bodies. *With wheel fairings the drag can go below Cd 0.12,as with the Cambridge University's 2013 CUER solar racer. -------------------------------------------------------------------------- *I don't recall any lift tables for the FKFS work.Kamm wasn't interested in lift so much as with crosswind stability.All the K-cars suffered gust effect stability issues.Koenig-Fachsenfeld patented a split-fin stabilizer as a palliative. -------------------------------------------------------------------------- *Typically,half-bodies do not generate lift in the general sense of how it is used. *Proper truncated half-bodies produce no separation 'over' the greenhouse area.All the drag is behind the body chop,acting like a drogue-chute. *Full-tail half-bodies have no separation at all and no wake as generally understood.As with barn doors,with enough horsepower and velocity they can be made to fly,but at 'normal' highway velocity it's not an issue. |
Recessed KammBack
The Box Cavity photo shows what I referred to as a recessed back KammBack configuration. And I realize that Renold's Number is involved -- but it has been many many years since my college fluid dynamics course and I need some help in learning whether a recessed KammBack would help reduce drag in a fluid denser than air (such as water) -- I am considering airfoil (hydrofoil) structures and plan to truncate as per the info posted above but would like to explore some calculations and am lost in the math. I don't have a clue as to how to mathematically treat or explore effect on drag (if any) as related to the recess distance back behind the outer projecting edge -- For that matter,
will the drag reduction of truncating downstream end of an airfoil (hydrofoil) in water have proportionally a similar effect as per info above for air as the fluid?? |
water
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*Water is 833X more dense than air and for proper Reynolds number 2-mph towing speed will represent 30-mph in air at full-scale,which gets your Rn above critical for turbulent boundary layer. *As to the mathematics,model scale testing has been preferred to CFD in some instances do the the complex nature of the 3D flow. *Kamm and his son tested cars underwater at the Stephens Institute at Hoboken,New Jersey. *The David Taylor Model Basin,Maryland,operated by the US NAVY is the most famous of these laboratories.Some of the human-powered submarine competitions take place in their facility. |
visual drag table
I added an image of the K-form wind tunnel test model at #7 permalink above
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a random sample of other tail investigations
Walter Lay's 1933, 4-configuration half-body model showed a range from Cd 0.30, to Cd 0.12, depending on tail length.
-------------------------------------------------------------------------------------- In 1934, Carl Breer, of Chrysler Corporation modified a DeSoto Airflow test mule. * Reshaping the car's tail, from a ducktail to a Koenig-Kamm chopped-tail lowered the drag from Cd 0.51, to Cd 0.268. * By adding a stinger, creating a full boat-tail they measured Cd 0.244. -------------------------------------------------------------------------------------- The circa-1935, FKFS Koenig-Kamm, 7-configuration, 1/2-body test model returned a range of Cd 0.258, to Cd 0.20, depending on tail length. -------------------------------------------------------------------------------------- Allegedly, there was a Cd 0.18, 'long-tail' variant of the 1946 Mathis V333, by Aerodynamicist, Jean Andreau. -------------------------------------------------------------------------------------- Porsche began running 'long-tail' variants at Le Mans, beginning around 1967, designed specifically for the Mulsanne Straight. -------------------------------------------------------------------------------------- Robert Cumberford was party to the 1973 design of a Cd 0.203 'city car', which, when fitted with a 72" boat-tail dropped to Cd 0.16. ------------------------------------------------------------------------------------- Daimler-Benz, Mercedes-Benz, 1978, C-111 III record car came in three flavors: Cd 0.237 Cd 0.195 Cd 0.178 depending on length of boat-tail. Setting a closed-course land speed record. -------------------------------------------------------------------------------------- In 1980, ITworks Volkswagen transporter received a push, from 27-mpg, to 34-mpg, thanks in part to a truncated boat-tail. -------------------------------------------------------------------------------------- Around 1981, NASA published results for their Ford E-100 Econoline modifications. * Adding the truncated boat-tail reduced the van from Cd 0.347, to Cd 0.242. * Adding their stinger only dropped the Cd to 0.238 ( this tail extension was embedded within turbulence ). ------------------------------------------------------------------------------------- Rolf Buchheim, of Volkswagen tested a short and long-tail 1981, VW Flow-Body, half-body, Cd 0.15 vs Cd 0.14 for the 'long-tail'. -------------------------------------------------------------------------------------- GM's 1982 Cd 0.23 Aero 2000, got stretched into the Cd 0.14 Aero 2002. -------------------------------------------------------------------------------------- General Motors used a 'long-tail' variant of their 1987, OLDSMOBILE AEROTECH record car for the long course at the Firestone Proving Grounds, Ft. Stockton, Texas, setting a closed-course land speed record. -------------------------------------------------------------------------------------- In 1990, ITworks' 'Spindletop' Honda CRX streamliner set a USFRA speed record at Bonneville. The boat-tail proved to provide the largest speed increase. -------------------------------------------------------------------------------------- Leaving Bonneville, Spindletop indicated it's highest mpgs, recorded to date at the time. Low 60s mpg at the old double-nickel speed limit. -------------------------------------------------------------------------------------- GM returned to Ft. Stockton in 1993, with a long-tailed GM Impact/ EV1, Cd 0.137 vs Cd 0.197, and set a closed-course land speed record for an electric car, at over 183-mph ( 100 + mpg equivalent, if combustion powered) ------------------------------------------------------------------------------------- You may have seen the 2005 AeroCivic. ------------------------------------------------------------------------------------ In 2014, the boat-tailed Spirit of Ecomodder indicated 6.3% lower drag than the 2013 Prius, tested at the same time at DARKO. Using the Prius as a calibration model ( tested @ DARKO, A2 Wind Tunnel, and Toyota ) SPIRIT indicated for Cd 0.243 @ A2, and Cd 0.234 @ Toyota. -------------------------------------------------------------------------------------- At the 2014 USFRA World of Speed, at Bonneville Int'l Speedway, the boat-tail helped add 9-mph to SPIRIT's top speed. -------------------------------------------------------------------------------------- The 2016 Mercedes-Benz IAA concept indicates for a drag reduction with it's extensible tail section ( Cd 0.19 ). -------------------------------------------------------------------------------------- And Mercedes-Benz 2022, EQXX concept also sports an active body elongation, helping with a Cd 0.1716. -------------------------------------------------------------------------------------- For a generic SUV, a boat-tail generates a delta-Cd 0.085 drag reduction ( 23.9% ), Ph.D. Joseph Katz, Professor, Aerospace Engineering, San Diego State University, MECHANIX ILLUSTRATED, March, 2017. -------------------------------------------------------------------------------------- ' the drag reduction from an elongated tail varies almost linearly with the reduction in cross section area.' Jeff Howell et al.,' Streamlined Tails-The Effects of Truncation on Aerodynamic Drag,', Loughborough University, Abstract, SAE Paper 2020-01-0673 |
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