The all parts of the EDF, except for the rotor adapter, are produced by Shapeways using SLS 3D printing in ’strong and flexible white plastic’. For the rotor adapter aluminium would have been a light weight and inexpensive choice. However, the threads in the part are relatively short and steel was chosen to ensure that the threads would not break when the bolts are tightened.
The figure below shows the produced prototype from the front and the rear.
(a)
(b)
Figure 4.10: The produced and assembled EDF from the front and the rear.
Chapter 5
Testing
The performance of the prototype EDF is tested in three experiments. In the first experi-ment the velocity profile at the nozzle outlet is measured to determine the mass flow through the EDF. Using the data a relation is derived between the mass flow and the outlet velocity measured at a reference position. In the second experiment the static performance is mea-sured. The EDF is not designed on static operation. However, static thrust is essential in take-off and therefore interesting. In the third experiment the dynamic thrust of the EDF is measured.
Below first a description of the set-up is given. Next the three experiments are discussed.
5.1 Setup
The figure below shows a schematic representation of the setup used in the static tests:
Figure 5.1: Schematic layout of the static test setup. The VCMD measures the input voltage and current. The DAQ and the laptop log the voltage, current and thrust data. The Elec-tronic Speed Controller(ESC) controls the motor. Here the servo-tester is used to control the throttle.
Al large part of the setup is reused from an earlier project[17]. With respect to the earlier setup, the pressure, temperature and rotational speed measurements are added. For the dynamic tests the same test setup is used. Only here a blower is added to create a non-zero inlet velocity. Below the different aspects of the setup are discussed.
5.1.1 EDF on slider with loadcell
The figure below shows the EDF mounted on the slider.
Figure 5.2: The EDF mounted on the slider with the loadcell to measure the thrust force.
Here the slider is connected to a loadcell to measure the thrust force. The loadcell is calibrated using weights. The calibration is discussed in section D.2. The loadcell gives an output signal between -10V and 10V. From the calibration follows that the thrust force can be determined using:
FT = −53.3Uloadcell− 0.35 (5.1)
The outlet signal is logged using a Data Acquisition Device(DAQ) and a laptop.
5.1.2 Powertrain
The figure below shows the components of the powertrain.
Figure 5.3: Components of the powertrain.
The EDF is powered using four lead batteries, 2 in series and 2 parallel. A voltage of 24V is supplied to the Electronic Speed Controller(ESC) which controls the motor speed.
The throttle is regulated by the user using a servo-tester connected to the ESC. In between the batteries and the ESC, a Voltage and Current Measurement Device(VCMD) is fitted to measure the ESC input voltage and current. The VCMD gives an output signal between -10V and 10V for both the current as the voltage. The measured voltage is determined by multiplying the output signal by 5. The measured current is determined by multiplying the output signal by 8.3A/V. Just as with the thrust measurement, the voltage and current are logged using a DAQ and a laptop. The maximum voltage and current the VCMD can handle are 24V and 83A.
5.1.3 Outlet pressures and temperature
The figures below show the pitot tube and the thermometer behind the EDF nozzle. The pitot tube pressures are read using two hand held manometers, also shown below.
(a) (b)
Figure 5.4: The pitot tube and thermometer behind the EDF(a) and the manometers used to read the pitot tube pressures.
The pitot tube measures the dynamic pressure and the static or total pressure behind the EDF. The static and static pressure are measured relative to the atmospheric pressure. The outlet temperature and pressures are used to determine the velocity behind and the mass flow through the EDF. The measurements are done at the outlet, instead of at the inlet to minimize the effect of disturbances in the flow made by the pitot tube and thermometer. The measurements are logged by hand.
5.1.4 Rotational speed
The rotational speed of the rotor is measured using a laser RPM meter. A reflector is placed on the spinner to work with the laser RPM meter. The figure below shows the RPM meter and the reflector on the spinner. The measured values are logged by hand.
(a) (b)
Figure 5.5: The laser RPM meter(a) and the reflector on the spinner(b) 5.1.5 Atmospheric pressure and temperature
The atmospheric pressure is measured using a barometer. The atmospheric temperature is measured using the same thermometer used for the outlet temperature. The measurements are logged by hand.
5.1.6 Blower
A blower is used to create a non-zero inlet velocity to measure the dynamic performance of the EDF. The blower is developed in a separate project [18]. The figure below shows the EDF with the blower.
Figure 5.6: The EDF positioned with the blower. Here denotes 1: the EDF, 2: a window that shows the rotor, 3: the upstream part of the blower, 4: the downstream part of the blower.
Here 1 denotes the EDF. The window, denoted by 2, shows the rotor such that the rotational speed can be measured. The blower consists out of two parts. The upstream part, denoted by 3, creates the inlet velocity and is fed by compressed air. The downstream part, denoted by 4, redirects the air upwards to minimize discomfort for the other persons in the lab. The EDF is positioned very close to the upstream blower part. The wind only blows through the EDF and not around it. This way the stream tube area is smaller which allows higher inlet velocities. The EDF does not touch the blower to make sure the thrust force can still be measured accurately. The blower is fed using compressed air. The velocity given by the blower can be controlled by a butterfly valve and a gate valve set in series.
In the upstream part of the blower some honeycomb sheets are used to create a uniform velocity profile and to decrease the turbulence. The velocity profile given by the blower has been measured without EDF. These measurements showed that the velocity profile is not completely uniform. The velocity is slightly higher in the center of the channel than on the sides. A maximum difference of approximately 8% in velocity is found. A maximum turbu-lence intensity of approximately 3% is measured. Here should be noted that the sample rate of the handheld manometers is approximately 1Hz. Therefore a large part of the spectrum of the velocity cannot be measured and the estimated turbulence intensity should be interpreted with care. More information about the exact construction and performance of the blower is given in [18].
More pictures of the setup with the blower are shown in D.1.