modelVelocity
Extends from Buildings.Fluid.Sensors.BaseClasses.PartialDynamicFlowSensor (Partial component to model sensors that measure flow properties using a dynamic model), Modelica.Icons.RoundSensor (Icon representing a round measurement device).
Information
This model outputs the flow velocity flowing from
port_a to port_b.
The sensor is ideal, i.e., it does not influence the fluid.
If the parameter tau is non-zero, then the measured
density that is used to convert the mass flow rate into
volumetric flow rate is computed using a first order differential equation.
Setting tau=0 is not recommend. See
Buildings.Fluid.Sensors.UsersGuide for an explanation.
Typical use and important parameters
In order to use the flow velocity sensor, the cross sectional area of the flow
channel crossSection must be specified in m2. For a
circular flow channel (e.g. a round pipe) of diameter diameter, the
cross sectional area can be specified as crossSection = diameter *
diameter / 4 * Modelica.Constants.pi. See
Buildings.Fluid.Sensors.Examples.Velocity for an example implementation
with diameter = 0.1.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Units.SI.Time | tau (from PartialDynamicFlowSensor) | 1 | Time constant at nominal flow rate (use tau=0 for steady-state sensor, but see user guide for potential problems) |
| Modelica.Units.SI.Area | A | Cross sectional area of flow channel | |
| Assumptions | |||
| Boolean | allowFlowReversal (from PartialTwoPort) | true | = false to simplify equations, assuming, but not enforcing, no flow reversal |
| Nominal condition | |||
| Modelica.Units.SI.MassFlowRate | m_flow_nominal (from PartialFlowSensor) | Nominal mass flow rate, used for regularization near zero flow | |
| Advanced | |||
| Modelica.Units.SI.MassFlowRate | m_flow_small (from PartialFlowSensor) | 1E-4*m_flow_nominal | For bi-directional flow, temperature is regularized in the region |m_flow| < m_flow_small (m_flow_small > 0 required) |
| Initialization | |||
| Modelica.Blocks.Types.Init | initType (from PartialDynamicFlowSensor) | Modelica.Blocks.Types.Init.InitialState | Type of initialization (InitialState and InitialOutput are identical) |
| Medium.Density | d_start | Medium.density(Medium.setState_pTX(p_start, T_start, X_start)) | Initial or guess value of density |
| Modelica.Units.SI.Temperature | T_start | Medium.T_default | Temperature used to compute d_start |
| Modelica.Units.SI.Pressure | p_start | Medium.p_default | Pressure used to compute d_start |
| Modelica.Units.SI.MassFraction[Medium.nX] | X_start | Medium.X_default | Mass fraction used to compute d_start |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Fluid.Interfaces.FluidPort_a | port_a (from PartialTwoPort) | Fluid connector a (positive design flow direction is from port_a to port_b) | |
| Modelica.Fluid.Interfaces.FluidPort_b | port_b (from PartialTwoPort) | Fluid connector b (positive design flow direction is from port_a to port_b) | |
| Modelica.Blocks.Interfaces.RealOutput | v | Flow velocity from port_a to port_b |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Units.SI.VolumeFlowRate | V_flow | Volume flow rate from port_a to port_b |
Revisions
-
June 25, 2026, by Michael Wetter:
Addednominalattribute to state variable.
This is for IBPSA, #2132. -
February 25, 2020, by Michael Wetter:
Changed icon to display its operating state.
This is for #1294. -
May 20, 2016, by Marcus Fuchs:
First implementation. Implementation is based on Buildings.Fluid.Sensors.VolumeFlowRate.