Update: Jason 2019-02-04

Short summary

  • Obtained mean velocity profile from the nozzle using an industrial anemometer
  •  Obtained thrust force vs. flow velocity plot utilizing RC benchmark and a thrust rig
  • Conducted flow disturbance test with two cases; at the center (case 1) and at the largest velocity gradient (case 2)

– Overall, general trends of aeroforces and and disturbance torques are repeatable
– Effect of aerodynmic force was affecting majorly for z-direction
– Effect of torque disturbance was affecting for x and y direction
– The highest torque peak (x direction) was observed for case 1, and the highest aerodynamic force peak (z direction) was observed for case 2.
– Large offset force of x direction, noisy signal from the accelerometer must be addressed in future, and using a largequad instead may worth to try

1. Mean velocity profile

In order to see the jet profile from 1.5 m far, I measured flow velocity at 9 different locations using an industrial anemometer. Each point were repeatedly measured five times. And the result is below;

Fig 1. Jet flow profile

Although it is not 100% symmetric, in general the profile is what we are expected. As shown in the plot, the largest velocity gradient occurs from -0.2~-0.3 m. Therefore, I made a set point to be ~0.3 m  for case 2.

2. Thrust vs. flow velocity

Fig 2. Thrust force experiments

I thought it might be interesting to see the wind flow effect in terms of thrust force on the quadcopter. A result plot is given in Fig 3.

Fig 3. Thrust force vs. velocity magnitude.

If I turn on the fan only without running the quadcopter, order of magnitude of thrust force was ~0.01 N. However, there is noticeable increase of thrust forces, if the quadcopter is running and the fan is on in the same time.  That makes sense because incoming flow can result in more rotation on propellers. However, this effect seems to be taken into account, to achieve a better flow disturbance reduction on the vehicle.

2. Flow disturbance repeatability

In order to see whether we can obtain repeatable wind disturbance effect, I conducted the experiment five times for each cases;

Case 1: quadcopter located at the center (x = 0.0 m)

Case 2: quadcopter located at the largest velocity gradient (x = -0.3 m)

The results are shown in Fig 4-7.

Fig 4. Torque disturbance at the center

Fig 5. Torque disturbance at the largest velocity gradient

  • Fig 6. Disturbance force at the center
  • Fig 7. Disturbance force at the largest velocity gradient

Overall, general trends of disturbance forces and and disturbance torques seemed repeatable.

Specifically, aerodynmic force was acting majorly on z-direction, and  torque disturbance was dominant for x and y direction.
Although there was not a significant differences between case 1 and case 2, the highest torque peak of x direction was observed for case 1, the highest torque peak of y direction was observed for case 2. That physically makes sense, since in case 1, flow in x direction is uniform, and that equally pushes the quadcopter, which results in more roll rather than pitch.

I think the effect will be more dramatic for case 2 if we locate the quadcopter near the nozzle, since more drastic velocity gradient will be applied to the vehicle.

The highest disturbance force peak (z direction) was observed for case 2, which might be concluded that force disturbance is more dominant when the large velocity gradient change occurs.

However, there is a large offset error of the force in x direction, which makes the analysis unreliable. Also, noisy signal from the accelerometer must be addressed in future.

For the future experiments, I am suggesting followings;

  1. I believe it might be worth to test with a largequad, since the largequad is more stable.
  2. It could be also interesting to see the difference when the quadcopter is located near the nozzle.
  3. I wish to make a vehicle produce some trajectory under flow disturbance, which mimics a realistic large wind shear scenario.