This is the interface between the fluid aspect of a pump/fan and a dynamic motor model in the signal aspect. The motor sends shaft speed (rev/min) to the fluid aspect’s mMotorSpeed term, and the fluid aspect returns shaft torque (N*m) from its mImpellerTorque term back to the motor.

This page has details on the exact terms to interface for various fluid link types.

The impeller torque term is negative because this torque is due to fluid resistance and opposes forward rotation of the impeller.

Below are some plots of the start-up profile of a typical air ventilation fan.

The fluid aspect can run without being attached to a dynamic motor. You can initialize the mMotorSpeed to a desired constant speed and let it run — this will create an ideal constant-speed impeller in your network.

It’s always a good idea to finish tuning the fluid aspect of a pump/fan before you integrate it with a dynamic motor. However, if you’ve already got the sim bus interface hooked up but still need to tune the fluid aspect without the dynamic motor interfering, there’s a trick to disconnect the fluid aspect from the motor during run-time. Set the fluid aspect’s mDriveRatio term to zero — this disconnects the impeller from the shaft. Then you can set the mImpellerSpeed to whatever you want for tuning. When done, set mDriveRatio back to it’s original value to reconnect it to the motor.

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