Inclusion of viscosity effects in a hydraulic circuit

Attached is the hydraulic circuit of my experimental setup. I have used three different oils. And have taken physical values of variation in RPM of the hydraulic motor. But the simulation results doesn't show any variation in motor speed with respect to the viscous influence. What must be added in the system to effectively evaluate the viscocity influence on hydraulic system?

have used hydraulic pipe lines that account for frictional resistance. Viscosity range used is from 32-460, The circuit only shows variation in speed only after 1000cSt.

Looking for help!

Thanks

Immanuel Keba

Answer 1

[Ronit]

Hello @immanuelkeba,

Most standard Simulink hydraulic motor blocks account pipe friction losses but do not account for the key viscosity-dependent losses inside the motor itself. In real systems, motor speed varies with viscosity mainly because:

• Volumetric losses (internal leakage) decrease with increasing viscosity, affecting flow and speed.
• Mechanical (friction) losses increase with higher viscosity, reducing motor efficiency.

Pipeline friction alone only significantly affects system behavior at very high viscosities (e.g., >1000 cSt), which is why you see little speed change in your current model.

To properly capture viscosity effects, you can try the following suggestions:

1. Use hydraulic motor (and pump) blocks that include volumetric and mechanical losses as functions of viscosity, or implement custom loss models.
2. Make sure fluid viscosity is defined correctly and propagated to all relevant components, not just pipes.
3. Add rotational damping (friction torque) and leakage flow elements that vary with viscosity.

Simply modeling pipe friction is insufficient. Including viscosity-dependent losses inside the motor/pump is essential for your simulation to reflect the real behavior of different oils in your hydraulic system.

I hope this resolves your query!