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Dynamometer
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Objective

To study the effect of load variations in  turbines with different blade configurations at different wind speeds. Student can measure and plot the Torque, Power and Efficiency characteristics of a Wind Turbine without having to change the actual design by forecasting  the running conditions for different blade parameters and tuning the load ..

Experiment Setup

A dynamometer is a set up used to measure the RPM, Torque and Power characteristics of a rotating prime mover. This could be a motor or an IC engine shaft, or more specifically in this experiment, a Wind Turbine. A hypothetical turbine is designed using computational fluid dynamics (CFD), and the torque obtained for this 3-bladed turbine is fed into a motor to simulate the real turbine shaft rotation. The rotating shaft is coupled to a generator with a programmable load. The power and efficiency characteristics of the actual turbine is studied with varying load. The resultant curves are plotted and post-processed by the student.

Description

A dynamometer consists of an absorption (or absorber/driver) unit, and usually includes a means for measuring torque and rotational speed. An absorption unit consists of some type of rotor in housing. The rotor is coupled to the engine or other equipment under test and is free to rotate at whatever speed is required for the test. Some means is provided to develop a braking torque between the rotor and housing of the dynamometer. The means for developing torque can be frictional, hydraulic, electromagnetic, or otherwise, according to the type of absorption/driver unit.

One means for measuring torque is to mount the dynamometer housing so that it is free to turn except as restrained by a torque arm. The housing can be made free to rotate by using trunnions connected to each end of the housing to support it in pedestal-mounted trunnion bearings. The torque arm is connected to the dyno housing and a weighing scale is positioned so that it measures the force exerted by the dyno housing in attempting to rotate. The torque is the force indicated by the scales multiplied by the length of the torque arm measured from the center of the dynamometer. A load cell transducer can be substituted for the scales in order to provide an electrical signal that is proportional to torque. We are using a torque meter which measures the torque and rpm of the motor.

Experimental Set-up:

A hypothetical turbine is designed using CFD for the blade profile design.  Based on this, numerical simulations already conducted for blade cross-sections applicable to chosen turbines are made available for selection. The selection process maybe with respect to velocity vector plots that show the streamlines and separation locations, or pressure plots integrated to provide the aerodynamic loads on the blades. The student is given the power range of the turbine he/she would like to design.The chosen blade profile, for chosen kW rating of turbine, is then fed into a motor by providing RPM from the CFD loads/torques. The motor runs at the CFD calculated rpm which effectively gives shaft rotation  rpm of the actual turbine designed by the student.

The student is required to study the plots of Power, torque and Efficiency of the turbine, and characterize the turbine performance.

As an example, the student may choose to design the aerodynamic profile of a 1kW turbine, and obtain the loads and RPM required to feed into the dynamometer setup. Typically, a NACA 4412 or 4212 airfoil profile would be chosen for this turbine. This can be simulated in a CFD software, which is readily available with solution plots, to estimate the required blade loading to produce the torque of a 1kW turbine. This torque can be divided into the Power to obtain the RPM, which is the final Mechanical Design ouput for the Dynamometer.

Typical CFD result for a 0012 profile 

The pressures can be integrated in the CFD program to obtain the desired loads and location of resultant forces. These loads are multiplied by the respective lever arm to produce the torque and RPM input for the Dynamometer motor. Then the user can study the electromechanical part by varying the generator loads on the turbine, and plot the Torque, Power and Efficiency characteristics.

The CFD analysis results from [3] and [4] has been made use of  for the design of this experiment.

The generator used for the  windturbine is WindBlue[2]. Windblue permanent magnet alternators come with its own rectifying unit.  A dc programmable  load is connected to adjust the load  from a remote location. The load curves are plotted for the picked blade profiles.

 

 

 

Cite this Simulator:

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