Update: Jason 2018-12-21

This week, I majorly focused on flow part of the research;

1. Checking the consistency of constant temperature anemometer (CTA)

• I have noticed that CTA does not show consistency, and I was trying to figure out which factor is causing this problem.
• The most significant phenomenon was that the measured voltage just drops down randomly, resulting in a significant change of velocity values.
• Currently, I am guessing that the electronics are malfunctioning since they are too old, but it is really difficult to figure out the source unless I can test this another CTA or electronics.
• By testing this many times, I realized that the circuit works properly for a couple of hours once it reaches proper level of voltage.

2. Time domain analysis for velocity near the nozzle

When the electronics was working properly, I tried to obtain the velocity w.r.t time, in order to analyze key flow parameters; $\bar{u}$ and $\left\langle u'^{2}\right\rangle$

Fig. 1. test specification

• Fan speed: 300 [rpm]
$\bar{u}=6.99\,[m/s]$, $\left\langle u'^{2}\right\rangle=0.33\,[m^2/s^2]$
the variance of fluctuation velocity is near to zero, which is desirable.

Fig. 2. velocity vs. time (fan speed: 300 [rpm])
• Fan speed: 600 [rpm]
$\bar{u}=13.84\,[m/s]$, $\left\langle u'^{2}\right\rangle=0.55\,[m^2/s^2]$
The average velocity was approx. two times of the previous case, which exactly matches with the doubling the fan speed. The variance was a bit higher than before.

Fig. 3. velocity vs. time (fan speed: 600 [rpm])
• Fan speed: 900 [rpm]
$\bar{u}=21.81\,[m/s]$, $\left\langle u'^{2}\right\rangle=1.43\,[m^2/s^2]$
The average velocity was approx. three times of 300 rpm case, which exactly matches with the tripling the fan speed. The variance was higher than before, since higher velocity resulted in more noise.

Fig. 4. velocity vs. time (fan speed: 900 [rpm])

3. Mean velocity profile

I measured several velocity points along the horizontal (x-axis) direction, in order to obtain mean velocity profile. The result is given in Fig. 6.

Fig. 5. Measuring velocity for horizontal (x-axis) direction

Fig. 6. Mean velocity profile with respect to x-axis

Although it is not 100% accurate measurement (since we do not have a linear stage), one can observe that the velocity profile is a slight notch shape, which can be found for a regular fan without flow straightener (honeycomb). Therefore, we can conclude that the current honeycomb does not ensure 100% uniform velocity profile, although it definitely helps to make the profile uniform.

From Jan 2, I am planning to

• See the flow profile with a certain distance (50cm, 100cm, 150cm), and try to quantify the flow properties. Also I will compare the result with the theoretical values.
• Double check the order of magnitude of the velocity with a portable velocity sensor
• Finish the simulation of torque disturbance