The CAFE Foundation is very pleased to offer a new array of important reports on extreme body drag reduction in its PAV Technology Library. These reports include work on Goldschmied propulsion that should prove valuable to any team planning to compete in the NASA Centennial Challenge flight competition.
Comments 4
I have been interested in this type of body ever since reading about it on the CAFE Foundation’s web page, though in reading through the papers that were posted, and those others that could be found online, I have yet to come across any more information on the CFD graphic that is posted. Would it be possible to be pointed towards the source of it. Hopefully a paper/journal that has more information. This body shape has great interest to me as it could well be used for a human powered submarine. The larger nose section would suit well a recumbent position. Thanks for your help, I am looking forward to seeing this blog progress.
Adam
Adam,
The graphic you mention is a pressure map of an early ‘Akron Body’ modification for more efficient airship propulsion. This shape was investigated as a straightforward adaptation of an existing form to utilize suction for boundary layer control and pressure thrust (for drag reduction purposes) but it would be a relatively poor choice for most other applications, including yours. Goldschmied’s later work showed how an optimum form incorporates natural laminar flow in a forebody portion, and a concave recovery section just past the point of flow transition to turbulence. You can read about them in several of his papers available here: http://cafefoundation.org/v2/tech_lib.php
In the pressure thrust paradigm, suction is utilized to augment the natural momentum of flow collapse into the aft section, and with the right body shape, near-zero drag is realistically achievable. Efficient, practical propulsion, however, is not, because the relationship between the ideal mass flow of suction-based drag reduction and the ideal mass flow of propulsion (within the available volume of the body) is diverging. Attempts to combine objectives will lead to exponential efficiency loss as the ingested fluid medium is tasked beyond simple restoration of boundary layer losses to provide a propulsive increase by inertial reaction.
It turns out that numerically optimized minimum drag bodies of revolution reveal ideal shapes for pressure thrust implementation in each Reynolds number range. Using the original blimp body instead would be inadvisable.
Thank you for the update. I have read through many of the papers, though briefly, but I could not see exactly how this particular graphic corresponded to them. I appreciate the information, and once again I am looking forward to seeing this blog progress.
Adam
I am currently an aerospace engineering student at California Polytechnic State University, San Luis Obispo. We are designing an electric general aviation 2-seater aircraft, and have decided to use a Goldschmied system. While we are confident with the fuselage shape and design, and firmly believe that the suction affect is beneficially worthwhile, I am stuck trying to determine if the ducted fan system for creating suction is also enough to create the propulsion necessary to overcome about 35 lbf of drag at 7500 ft and 80 knots cruise speed. Goldschmied claims that this can be done for a similar type craft at 200 mph but I was wondering what anyone thought on the matter? Thank you