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Model Van in Wind Tunnel
Gasoline prices in America have been sharply increasing these past two years and are projected to increase even more. Americans have been feeling the pressure of higher gas prices even more due to the popularity of bigger and more powerful vehicles like sport-utility vehicles (SUVs) and minivans. About 50% of a vehicle's fuel consumption at 50-mph is in overcoming air resistance. Hence reducing air resistance by say 10% can increase the fuel mileage (miles per gallon) by 5%. Since air resistance increases as the square of the speed, the effect of reducing aerodynamic drag increases with speed.

We began to ponder if our Sinha Flexible Composite Surface Deturbulator (FCSD) could help in this area. The Deturbulator reduced drag on airfoils by overcoming skin friction. However, the major source of drag for road vehicles is pressure drag, resulting from a large separated and very turbulent wake. Could a thin Deturbulator tape do anything significant to such a large region of turbulent flow? Our youngest employee, 10th grade high-school student Sumontro Sinha believed the Deturbulator could do it and proceeded to verify it as his 2006 Science Fair Project.

It is very difficult to streamline a road vehicle like an airfoil and still preserve its functionality. Even though auto manufacturers are coming up with more streamlined shapes, the net result is still far from ideal. A large region of separated flow exists behind all vehicles as evidenced from a large plume of spray when driving on wet highways. The problem is even more acute with large trucks and tractor trailers, where the rear end is virtually unstreamlined.

Initial tests by Sumontro in the Sinhatech wind tunnel on a 1/24th scale Cadillac Escalade showed the possibility of 80% drag reduction with a FCSD (Fig 1)! The Deturbulator killed the turbulence in the shear layer that provides traction for driving the large eddies. Consequently the main flow slides past leaving a region of stagnant air behind the vehicle as shown in Fig 2. The stagnant air behaves as a virtual streamlined boat-tail extension. Since the air is stagnant within this boat-tail no turbulent dissipation of flow energy takes place. Such dissipation is the main reason why the pressure in a separated wake is much lower than the free stream, giving rise to pressure drag.


Fig 1. Drag of Model Cadillac Escalade in Wind Tunnel




Fig 2. Method of Reducing Drag of a Bluff Body, such as an Automobile, with Deturbulator

Even though the small-scale wind tunnel tests were successful it was unclear whether the Deturbulator would work on a full scale vehicle. Tests on Dr. Sinha's 2000-Honda Odyssey minivan provided the final proof. The Odyssey normally yielded about 23 miles per gallon for combined city-highway driving and 26 miles per gallon on the highway at speeds between 55-75 mph. The FCSD treated Odyssey yielded about 26 miles per gallon in combined city/highway driving and 31 mpg on the highway. These figures (Figs 3 and 4) were obtained by averaging data from several trips and have a 93% statistical significance level. The gas tank was topped before and after each trip. The trip distance and type (i.e., highway or city) were also noted.


Fig 3. Minivan Highway Fuel Economy Improvement (Control: Untreated; Experimental: Deturbulator)


Fig 4. Minivan City plus Highway Combined Fuel Economy Improvement due to Deturbulator (Experiment)

As further evidence that turbulent mixing in the wake of the van was reduced, two Honda Odysseys were driven down a dusty country road together. Afterward, the dust collected on the rear windows was examined. As shown in Figs 4 and 5, the Odyssey treated with FCSD had collected much less dust than the other one.


Fig 5. Standard Odyssey
After Driving Dusty Road

Fig 6. FCSD Treated Odyssey
After Driving Same Road

The next tests were conducted on a 1997 Dodge Dakota pickup truck. The truck is equipped with a fuel economy meter that provides instantaneous and average miles per gallon for each trip. Fig 7 shows the miles per gallon before and after applying the Deturbulator at 55 and 65 miles per hour. These figures are based on repeatedly running the truck back and forth at the above speeds on a level section of highway near Oxford, Mississippi while noting the instantaneous mpg readings. This data has a statistical significance level of 99.99%. Actual driving on the highway at a variety of speeds indicated an increase from 19.9 to 21.8 miles per gallon due to the Deturbulator.


Fig 7. Fuel Economy Improvement due to Deturbulator (Experimental) on Pickup Truck

The deturbulator stabilized the wake behind the minivan as evidenced from a cleaner rear windshield and stagnant oil flow visualization patterns on the rear.

While additional road-tests and optimization of the Deturbulator installation is currently ongoing, SINHATECH plans to offer Deturbulator installations at a nominal price for all varieties of road vehicles within a month. In the meantime, Sumontro's project won him the First Prize in the Engineering-Mathematics-Computers category at the 2006 Mississippi Science and Engineering State Fair.

Through the Auto-Deturbulator, Sinhatech has the potential of helping Americans keep their existing vehicles without going broke paying for fuel or upgrades. It can also save the U.S. about $32 billion per year in oil often imported from unstable regions of the world and help reduce the pollution and greenhouse gas (CO2) emission from an estimated 225 million automobiles and trucks on American roads (Department of Transportation Statistics 2000).

HOW DOES THE DETURBULATOR COMPARE:

The drag reduction corresponding to measured fuel economy improvements is about 30-40%. This is not only higher than those with traditional methods which try to reduce the size of the wake with vortex generators (see table below) but already exceeds the 8.1% increase in miles per gallon called for 2008-2011 model years in the new Federal standards for SUVs and light trucks.



Semi-Tractor-Trailer Rigs

A grant from the National Science Foundation has been awarded to investigate deturbulation of semitrailer rigs. Testing has been performed on a deturbulated 2004 Freightliner Columbia double-sleeper tractor pulling a Wabash 53-ft box semi-trailer. The mileage data was obtained independently by the trucking company during normal roundtrip operation with cargo between Baton Rouge, LA and Pensacola, FL. The following graph from driver records shows 4% better mileage for overall driving, including idling periods, and 5% improvement on the highway. The truck cpu gave 5.95 mpg normally versus 6.26 mpg when deturbulated for overall trip mileage. Since then, we have extended the treatment and preliminary data indicate 6.6 mpg or 10% better overall mileage. These test runs were performed in typically humid conditions indicating that the version 2 deturbulator is not adversely affected by humidity.



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