Tuesday, May 31, 2011

Virtual Wind Tunnel: Streamlines U (Air Speed)


The pictures below show the streamlines for the CFD "virtual wind tunnel" simulation of a Kyosho Mini-Z MR03 Mazda 787b 3D model, "racing" at 10 m/s (36 km/h).

In this type of simulation a streamline is the theoretical path that a particle flowing around the vehicle would describe.

There are five different pictures, one for each of the following rear wing configurations: no wing, flat wing, 45 degree wing, gurney flap, scoop wing. 

Both the car and lines are colored according to the air speed. Red represents high air speed (11 m/s) and blue represents low air speed (5 m/s).

No Wing - Air Speed
Flat Wing - Air Speed
45 Degree Wing - Air Speed

Gurney Flap - Air Speed

Scoop Wing - Air Speed

For complete results of the Mini-Z MR-03 CFD "virtual wind tunnel" simulation click here.

Monday, May 30, 2011

Virtual Wind Tunnel: Streamlines Cp (Pressure Coefficient)

The pictures below show the streamlines for the CFD "virtual wind tunnel" simulation of a Kyosho Mini-Z MR03 Mazda 787b 3D model, "racing" at 10 m/s (36 km/h).

In this type of simulation a streamline is the theoretical path that a particle flowing around the vehicle would describe.

There are five different pictures, one for each of the following rear wing configurations: no wing, flat wing, 45 degree wing, gurney flap, scoop wing. 

Both the car and lines are colored according to the pressure coefficient (Cp). Red represents higher pressure regions, blue represents lower pressure ones.

No Wing - Cp
Flat Wing - Cp
45 Degree Wing - Cp

Gurney Flap - Cp

Scoop Wing - Cp

For complete results of the Mini-Z MR-03 CFD "virtual wind tunnel" simulation click here.

Saturday, May 28, 2011

Virtual Wind Tunnel: Forces vs. Speed

The charts below show the results of a CFD "virtual wind tunnel" simulation of a Kyosho Mini-Z MR03 Mazda 787b 3D Model.

The first chart shows the increase in drag force as a function of speed. The second chart shows the relationship between down force (or lift) and speed. Both charts show the data points and curves for each one of the different rear wing configurations tested in the simulations: no rear wingflat rear wing15 degree rear wing30 degree rear wing45 degree rear wing60 degree rear wing, gurney flapscoop wing.

Each data point on each chart represents a different simulation, conducted at a different speed: 2.5 m/s (9km/h), 5.0 m/s (18 km/h) , 7.5 m/s (27 km/h), and 10 m/s (36 km/h). This should cover practically the full range of speeds observed in a typical Mini-Z track.

The curves were interpolated using a 2nd order polynomial. In all cases the fit was almost perfect (R-squared greater than 0.98) indicating that, according to the simulation, both drag and down forces increase as a proportion of speed squared. These results are pretty much in line with basic aerodynamics laws.


For complete results of the Mini-Z MR-03 CFD "virtual wind tunnel" simulation click here.

Virtual Wind Tunnel: Drag vs. Down Force Trade Off

The chart below shows the overall results for a CFD "virtual wind tunnel" simulation of a Mini-Z MR03 Mazda 787b 3D model, "racing" at 10 m/s (36 km/h).

Each data point on the chart corresponds to a different rear wing configuration: no rear wingflat rear wing15 degree rear wing30 degree rear wing45 degree rear wing60 degree rear wing. Also on the chart are the results for a gurney flap and for a scoop wing. The drag force for each configuration is shown on the horizontal axis. The vertical axis shows the down force (or lift, for negative values). All forces are shown in gf.


According to the simulation results, there is a clear benefit of using practically any type of wing, even a flat one. This benefit comes from neutralizing the lift effect generated by the body shell itself. The greater the angle of the rear wing, the greater the benefit in terms of down force. This benefit, however, comes at the cost of increased drag.

The results indicate that, for the wing geometries tested, the sweet spot in terms of the drag vs. down force trade off might be close to the 30 degree configuration. Above that, increases in rear wing angle seem to bring only marginal improvements in down force while still increasing drag.

A gurney flap, according to the simulation, might be a good alternative providing a down force between the 15 and 30 degree wings with less drag.

A scoop wing configuration is the clear choice in terms of down force alone but, at the same time, it is the one with the highest drag.

For complete results of the Mini-Z MR-03 CFD "virtual wind tunnel" simulation click here.

Virtual Wind Tunnel: May 28, 2011 Update

This is a general update on all the recent CFD "virtual wind tunnel" simulations of a Kyosho Mini-Z MR03 Mazda 787b 3D model.


In addition to the configurations tested previously (no wing, flat rear wing, 45 degree rear wing) three additional ones were considered: 15 degree, 30 degree, and 60 degree. This gives a pretty complete range of rear wing angles and may help understand aerodynamic effects at the Mini-Z scale and speed.


In order to make the results comparable I had to re-design the previously tested 45 degree configuration and run the simulation again. As the results changed I updated the previous posts, so all published results are consistent and comparable.


The table below shows drag and down forces for the different rear wing configurations tested:

Drag (gf)
Down Force (gf)
No Rear Wing
6.2
- 7.8 (lift)
0o Rear Wing
6.6
- 0.5 (lift)
15o Rear Wing
7.7
4.6
30o Rear Wing
8.9
8.0
45o Rear Wing
10.1
8.5
60o Rear Wing
10.6
9.3

All simulations were done considering the car "racing" at 10 m/s (36 km/h).

Once again, all results come from a computer simulation of a Mini-Z 3D model, resembling a Mazda 787b car body. None of the results have been validated empirically at a real wind tunnel, so all the typical CFD caveats apply.

Detailed results and pictures for each of the simulations are posted in the following links:

Virtual Wind Tunnel: No Rear Wing
Virtual Wind Tunnel: Flat Rear Wing
Virtual Wind Tunnel: 15 Degree Rear Wing

Virtual Wind Tunnel: 30 Degree Rear Wing
Virtual Wind Tunnel: 45 Degree Rear Wing
Virtual Wind Tunnel: 60 Degree Rear Wing

Virtual Wind Tunnel: 60 Degree Rear Wing

These are the results of a CFD "virtual wind tunnel" simulation of a Mini-Z MR03 Mazda 787b 3D model with a 60 degree rear wing.

The drag force recorded by the simulation while the car was "racing" at 10 m/s (36 km/h) was 10.6 gf. The down force recorded by the simulation at this speed was 9.3 gf.

The pictures below show the pressure coefficient (Cp) indicating high (red) and low (blue) pressure areas.










Virtual Wind Tunnel: 30 Degree Rear Wing


These are the results of a CFD "virtual wind tunnel" simulation of a Mini-Z MR03 Mazda 787b 3D model with a 30 degree rear wing.

The drag force recorded by the simulation while the car was "racing" at 10 m/s (36 km/h) was 8.9 gf. The down force recorded by the simulation at this speed was 8.0 gf.

Friday, May 27, 2011

Virtual Wind Tunnel: 15 Degree Rear Wing


These are the results of a CFD "virtual wind tunnel" simulation of a Mini-Z MR03 Mazda 787b 3D model with a 15 degree rear wing.

The drag force recorded by the simulation while the car was "racing" at 10 m/s (36 km/h) was 7.7 gf. The down force recorded by the simulation at this speed was 4.6 gf.

The pictures below show the pressure coefficient (Cp) indicating high (red) and low (blue) pressure areas.







Saturday, May 21, 2011

Virtual Wind Tunnel: No Wing vs. Flat Wing vs. 45 Degree Wing


I have completed a set of three CFD "virtual wind tunnel" simulations of a Mini-Z MR03 Mazda 787b 3D model and I think the findings are quite interesting.

The table below shows drag and down forces for the three different rear wing configurations tested:

Drag (gf)
Down Force (gf)
No Rear Wing
6.2
- 7.8
Flat Rear Wing
6.6
- 0.5
45o Rear Wing
10.1
8.5

All simulations were done considering the car "racing" at 10 m/s (36 km/h).

The first interesting finding is that, according to the simulation results, a Typical Mini-Z body shell like the Mazda 787b ASC generates 7.8 gf of lift when ran with no rear wing. At 10 m/s (36km/h) this force can be significant, close to 5% of the car weight.

A second finding is that adding a simple flat rear wing can, somehow, reduce the lift force to 0.5 gf, practically neutralizing its effect. This benefit comes at no material penalty in drag, as the increase observed in the drag force was just 0.4 gf.

Finally, by using a 45 degree rear wing a down force of 8.5 gf can be achieved. This result however comes along with a 3.5 gf increase in drag.

Detailed results for each of the three simulations are posted in the following links:

Virtual Wind Tunnel: No Rear Wing
Virtual Wind Tunnel: Flat Rear Wing
Virtual Wind Tunnel: 45 Degree Rear Wing

Virtual Wind Tunnel: No Rear Wing

These are the results of a CFD "virtual wind tunnel" simulation of a Kyosho Mini-Z MR03 Mazda 787b 3D model with no rear wing.

The drag force recorded by the simulation while the car was "racing" at 10 m/s (36 km/h) was 6.2 gf. The down force recorded by the simulation at this speed was -7.8 gf (that is, 7.8 gf of lift).

The pictures below show the pressure coefficient (Cp) indicating high (red) and low (blue) pressure areas.









Virtual Wind Tunnel: Flat Rear Wing

These are the results of a CFD "virtual wind tunnel" simulation of a Mini-Z MR03 Mazda 787b 3D model with a flat rear wing.

The drag force recorded by the simulation while the car was "racing" at 10 m/s (36 km/h) was 6.6 gf. The down force recorded by the simulation at this speed was -0.5 gf (that is, 0.5 gf of lift).

The pictures below show the pressure coefficient (Cp) indicating high (red) and low (blue) pressure areas.









Virtual Wind Tunnel: 45 Degree Rear Wing

These are the results of a CFD "virtual wind tunnel" simulation of a Kyosho Mini-Z MR03 Mazda 787b 3D model with a 45 degree rear wing.

The drag force recorded by the simulation while the car was "racing" at 10 m/s (36 km/h) was 10.1 gf. The down force recorded by the simulation at this speed was 8.5 gf.

The pictures below show the pressure coefficient (Cp) indicating high (red) and low (blue) pressure areas.