WOLFRAM SYSTEM MODELER

PartialStaggeredFlowModel

Base class for momentum balances in flow models

Wolfram Language

In[1]:=

SystemModel["Modelica.Fluid.Pipes.BaseClasses.FlowModels.PartialStaggeredFlowModel"]

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Information

This information is part of the Modelica Standard Library maintained by the Modelica Association.

This partial model defines a common interface for m=n-1 flow models between n device segments. The flow models provide a steady-state or dynamic momentum balance using an upwind discretization scheme per default. Extending models must add pressure loss terms for friction and gravity.

The fluid is specified in the interface with the thermodynamic states[n] for a given Medium model. The geometry is specified with the pathLengths[n-1] between the device segments as well as with the crossAreas[n] and the roughnesses[n] of the device segments. Moreover the fluid flow is characterized for different types of devices by the characteristic dimensions[n] and the average velocities vs[n] of fluid flow in the device segments. See Pipes.BaseClasses.CharacteristicNumbers.ReynoldsNumber for example definitions.

The parameter Re_turbulent can be specified for the least mass flow rate of the turbulent regime. It defaults to 4000, which is appropriate for pipe flow. The m_flows_turbulent[n-1] resulting from Re_turbulent can optionally be calculated together with the Reynolds numbers Res[n] of the device segments (show_Res=true).

Using the thermodynamic states[n] of the device segments, the densities rhos[n] and the dynamic viscosities mus[n] of the segments as well as the actual densities rhos_act[n-1] and the actual viscosities mus_act[n-1] of the flows are predefined in this base model. Note that no events are raised on flow reversal. This needs to be treated by an extending model, e.g., with numerical smoothing or by raising events as appropriate.

Parameters (13)

m	Value: n - 1 Type: Integer Description: Number of flow segments
n	Value: 2 Type: Integer Description: Number of discrete flow volumes
nParallel	Value: Type: Real Description: Number of identical parallel flow devices
g	Value: system.g Type: Acceleration (m/s²) Description: Constant gravity acceleration
allowFlowReversal	Value: system.allowFlowReversal Type: Boolean Description: = true, if flow reversal is enabled, otherwise restrict flow to design direction (states[1] -> states[n+1])
momentumDynamics	Value: system.momentumDynamics Type: Dynamics Description: Formulation of momentum balance
m_flow_start	Value: system.m_flow_start Type: MassFlowRate (kg/s) Description: Start value of mass flow rates
p_a_start	Value: Type: AbsolutePressure (Pa) Description: Start value for p[1] at design inflow
p_b_start	Value: Type: AbsolutePressure (Pa) Description: Start value for p[n+1] at design outflow
useUpstreamScheme	Value: true Type: Boolean Description: = false to average upstream and downstream properties across flow segments
use_Ib_flows	Value: momentumDynamics <> Types.Dynamics.SteadyState Type: Boolean Description: = true to consider differences in flow of momentum through boundaries
Re_turbulent	Value: 4000 Type: ReynoldsNumber Description: Start of turbulent regime, depending on type of flow device
show_Res	Value: false Type: Boolean Description: = true, if Reynolds numbers are included for plotting

Inputs (7)

pathLengths	Type: Length[m] (m) Description: Lengths along flow path
states	Type: ThermodynamicState[n] Description: Thermodynamic states along design flow
vs	Type: Velocity[n] (m/s) Description: Mean velocities of fluid flow
crossAreas	Type: Area[n] (m²) Description: Cross flow areas at segment boundaries
dimensions	Type: Length[n] (m) Description: Characteristic dimensions for fluid flow (diameters for pipe flow)
roughnesses	Type: Roughness[n] (m) Description: Average height of surface asperities
dheights	Type: Length[n - 1] (m) Description: Height(states[2:n]) - Height(states[1:n-1])