The Fan Car

     The idea to reduce Drag and/or improve Downforce on a vehicle using fans at the rear has been around for decades. Specially in the world of motorsports. Examples include Gordon Murray's BT46 and the T50. Here an explanation is made as to why placing a fan behind a car or a container-carrier truck can be used to improve fuel economy.

     The sample car model is of the renowned Ahmed Body. For validation of the numerical simulation, please refer to this post.

     Fig. 1 shows pressure isosurfaces around the car body both with and without fans installed at the rear. It is clear that the pressure difference between rear and front of the car is more when the fans are not available. More pressure difference results in more Drag and a relatively bad fuel economy.

Fig. 1, T-B; Fan disabled, fan enabled

     Fig. 2 shows cross section view of the car. It can be seen that the the boundary layer is re-energized and as a result the flow separation is significantly reduced by adding a fan at the rear. By adding a fan, the vortices are not only moved away from the rear-end of the car but also have smaller size and less intensity, as shown in Fig. 3.

Fig. 2, T-B; Fan disabled, fan enabled. Red arrows represent direction of airflow

Fig. 3, L-R; Fan disabled, fan enabled

Thank you for reading. Please share my work. If you would like to collaborate on a project please reach out.

Pipe Flow Simulation

Just ran another simulation related to HMT, this problem became steady state after about 36 seconds.

Water at 318 K starts flowing (0.00035 m^3/s) through a steel pipe initially at 298 K. The steel pipe had convection to air at 298 K at 3,000 W/m^2.K. A simple simulation yielded inner and outer wall temperatures of the pipe to be 309.07 K and 311.26 K respectively. Then I ran a transient simulation, to find out the time taken by the pipe’s walls to reach these temperatures (f...rom 298 K) as water flows through it. It came out to be around 36 seconds.

Then I ran a FEA. To calculate stresses induced in the pipe due to water pressure, thermal effects, gravity etc. The pipe’s diameter increased by 0.005866 mm and von-mises stress induced was 117,016,056 N/m^2 with a factor of safety of 5.302.

Then I ran fatigue study to see if the pipe will survive under these loads for 20 years or not. It will I think. The fatigue S-N curves were not available so I used the ones for carbon steel (slightly different from the ones I used for CFD analysis and FEA); so will it last for 20 years I am not sure yet (searching for curves).

 Temperatures at inner wall surface

 Temperature at outer wall surface

displacement and stress animation

Canal Turbine Concept

It's a concept I am currently working on, so far I gave made a CAD model (renderings attached) of it in SolidWorks and analyzed it using its built in CFD module.

There are many advantages of canal turbines over wind turbines, prominent one's being:

 

Unidirectional flow

Water flows in one direction in a canal so we don't need pitch and yaw control surfaces. That simplifies the design process and reduces weight.

Constant flow rate

We (humans) control water flow rate through canals and it's almost same all year, so we don't have to worry about blade aero foil design to suit variable/abruptly variable flow rate, that makes design process further straight forward.

Large Electricity potential

Canals are 100s of km long, imagine the electricity potential in the canals. You can put these turbines in irrigation canals and it'll power nearby villages and all the irrigation equipment etc.

Higher Power/Discharge Ratio

Water is ~816 times dense (powerful) than air, so for the same discharge (flow) rate we get potentially 816 times more power. Which means more we can make designs that are lighter, smaller and easier to manage and maintain.

Easy maintenance

Fitted less than ~1 m deep inside the canal and can be retracted for maintenance at ground level, making maintenance very easy or better yet, we can maintain them while canals are being cleaned.

Comparison between Lift and Drag Produced by a Legacy Wing VS a Wing with Tubercles (Humpback Whale Fin's Inspired)

* Link for Plots (now showing here for some reason) http://3dimensionaldesigningandmanufacturing.blogspot.com/2015/07/plots-for-comparison-between-lift-and.html

Following data was obtained from the CFD Simulations carried out in SolidWorks Flow Simulation Premium.

Project: Design of a Wing/Blade with Tubercles for Airplanes and/or Turbines

Without Tubercles
Air Speed in Km/h	Lift in N	Drag in N
150	46.307	14.775
140	39.942	12.917
130	33.432	11.057
120	28.807	9.498
110	24.234	7.928
100	20.593	6.625
90	15.836	5.352
80	12.482	4.205
70	9.411	3.243
60	7.272	2.406
50	4.873	1.680
40	3.130	1.082
30	1.763	0.612
20	0.810	0.279
10	0.231	0.072

 

 

With Tubercles
Air Speed in Km/h	Lift in N	Drag in N
150	50.616	11.360
140	48.131	10.008
130	37.190	8.505
120	30.988	7.309
110	24.784	6.079
100	20.892	5.094
90	17.225	4.146
80	13.412	3.287
70	9.955	2.507
60	7.444	1.849
50	4.955	1.286
40	2.991	0.828
30	1.652	0.468
20	0.725	0.212
10	0.214	0.057

 

Comparison between Lift and Drag

Air Speed in Km/h	Percentage Less Drag		Percentage More Lift
150	23.113		8.513
140	22.520		17.014
130	23.080		10.105
120	22.974		7.038
110	23.322		2.219
100	23.109		1.431
90	22.534		8.064
80	21.831		6.934
70	22.695		5.465
60	23.150		2.311
50	23.452		1.655
40	23.475		-7.523
30	23.529		-6.719
20	24.014		-11.72
10	20.833		-7.94

 

It is clear that the wing with tubercles not only produces more lift at a particular velocity but also less drag.

Data for the Wing without Tubercles:

Wing Span: 1.07 m

Chord Length: 0.229 m

Air Velocity: 0-150 Km/h head on

Vertical Pitch: 0 Degree

Gravity Considered

Fluid: Dry Air at STP

Mesh Settings: Coarse (3/8)

Data for the Wing with Tubercles:

Wing Span: 1.067 m

Chord Length Large: 0.229 m

Chord Length Small: 0.203 m

Air Velocity: 0-150 Km/h head on

Vertical Pitch: 0 Degree

Gravity Considered

Fluid: Dry Air at STP

Mesh Settings: Coarse (3/8)

Let's now take a look at visual representation of data.

This Plot Shows Air Velocity VS Drag, Lift by the Wing without Tubercles

This Plot Shows Air Velocity VS Drag, Lift by the Wing with Tubercles

As you can see from above two plots; the wing with tubercles generates more lift and less drag.

This Plot Shows Air Velocity VS Lift Generated by the Wings

The green line represents the Lift generated by the wing with tubercles. It is between two to six percent more at each velocity.

This Plot Shows Air Velocity VS Drag Generated by the Wings

The green line represents the Drag generated by the wing with tubercles. It is around twenty two percent less at each velocity.

This Plot Shows Air velocity VS Lift to Drag Ratio

It is clear from this plot that Lift to Drag ratio of the wing with tubercles is around thirty three percent more for the wing without tubercles at a velocity point.

 

This Plot Shows Air Flow around the Wings at 150 Km/h from the Right Side

This Plot Shows Air Flow around the Wings at 150 Km/h

The Need for Tubercles

In aviation there are four forces at play, Lift which over comes Weight and Thrust which overcomes Drag. For a cruise speed at a particular altitude, three of these forces are almost constant. Our goal is to minimize Thrust, Drag and Weight and maximize Lift, this is because Thrust costs in terms of fuel flow rate and Weight and Drag negatively impacts on the agility of the aircraft. Aerodynamically efficient Wings and/or Blades with "Tubercles" will not only increase Lift and but also decrease Drag. This all means that we will need less Thrust for a cruise speed than before, that results in savings in terms of fuel which will result in healthier environment.

 

Applications:

 

Canal Turbine Concept

It's a concept I am currently working on, so far I gave made a CAD model (renderings attached) of it in SolidWorks and analyzed it using its built in CFD module.

There are many advantages of canal turbines over wind turbines, prominent one's being:

 

Unidirectional flow

Water flows in one direction in a canal so we don't need pitch and yaw control surfaces. That simplifies the design process and reduces weight.

Constant flow rate

We (humans) control water flow rate through canals and it's almost same all year, so we don't have to worry about blade aero foil design to suit variable/abruptly variable flow rate, that makes design process further straight forward.

Large Electricity potential

Canals are 100s of km long, imagine the electricity potential in the canals. You can put these turbines in irrigation canals and it'll power nearby villages and all the irrigation equipment etc.

Higher Power/Discharge Ratio

Water is ~816 times dense (powerful) than air, so for the same discharge (flow) rate we get potentially 816 times more power. Which means more we can make designs that are lighter, smaller and easier to manage and maintain.

Easy maintenance

Fitted less than ~1 m deep inside the canal and can be retracted for maintenance at ground level, making maintenance very easy or better yet, we can maintain them while canals are being cleaned.