SPEEDGEL PIV TESTING NAQI
Harm Ubbens, Project mananger aerodynamics Flanders' Bike Valley
With the use of particle image velocimetry (PIV), the effect of the NAQI Aero Speedgel is visualised on a PVC cylinder in a wind tunnel. With the use of small oil particles the flow around an object can be traced and visualised using this measurement method. By performing two measurements - one measurement of the bare cylinder and one measurement of the cylinder with Speedgel applied to it - the aerodynamic effect of the Speedgel ban be shown.
The setup is installed such that the laser illuminates the oil particles from the side and the camera captures the images from the top to see the flow around the cylinder installed vertically in the wind tunnel as can be seen in Figure 1.
Figure 1 - Measurement setup
As the measurement setup made use of planar PIV the particles on the rear side of the cylinder (as seen from the laser) are not enlightened as they are in the shadow of the cylinder itself as can be seen in figure 2. This will result in an unstable region in the figures at this location as a result of camera noise.
Figure 2 - Camera output with shadow region behind the cylinder
The NAQI Aero Speedgel that was used to conduct the testing was the OM20 speedoil (Figure 3). This speedoil was previously used in investigations in the wind tunnel on real riders where it showed a decrease in aerodynamic resistance on each rider tested.
Figure 3 - OM20 speedoil applied to the cylinder
The result of the PIV measurements can be found in Figures 4 and 5.
Figure 4 - PIV figure of the cylinder without product.
Figure 5 - PIV figure of the cylinder with OM20 speedoil
As can be seen in the figures the region blocked by the cylinder (above the cylinder in this orientation) shows a region ith noise and airspeeds around 0M/s. This region should therefore be neglected during the analysis of the PIV figures.
In the PIV figures the wind flows from legt-to-right with an airspeed of 14m/s. This results in a stagnation point on the LHS of the cylinder and a low-velocity unsteady wake on the RHS of the cylinder. It is clearly seen that the speedoil influences the airflow around the cylinder. Due to the increased roughness the separation point is pushed backwards on the cylinder and the severity and size of the wake are reduced. This will cause the pressure difference between the front and rear part of the cylinder to be lower in the case with the speedoil. A lower pressure difference means a lower pressure drag. As the pressure drag is the main contributor of the total drag for a bluff body the total drag is reduced as well.
Author - Harm Ubbens, Project manager aerodynamics
Flanders' Bike Valley, Tervantstraat 2B - 3583 Beringen, Belgium
tel:+32(0)468 29 63 16, Email: firstname.lastname@example.org