Assigned Flow

The Assigned Flow junction type allows you to connect one pipe and to input a known steady-state and/or transient flowrate entering or leaving at a particular location. An irrecoverable loss can also be included.

The Assigned Flow Properties window follows the first of the two basic Properties window formats, displaying the connecting pipe information in a fixed format. Depending on whether you specify the junction as an inflow or outflow type, the required connecting pipe (upstream/inlet or downstream/outlet) will be enabled while the other pipe is disabled. Note that if the flow is specified as Inflow (to the system) then the reference positive flow direction of the connected pipe must be away from the junction (i.e. the junction is upstream of the pipe).

The Assigned Flow junction will automatically switch the inflow/outflow parameter based on the reference flow direction of the connected pipe.

The Assigned Flow junction type allows you to specify positive flow rates as volumetric or mass flow rates. Negative flow rates are not accepted for steady flow, although they are for transient flow. If, for example, you have an outflow type junction and your system is physically flowing in, you cannot assign a negative flow rate to the junction. You must reverse the connecting pipe flow direction to be consistent with the actual direction and change from an outflow type to an inflow type.

Transient Data

On the transient data tab a flowrate transient can be entered. A special feature is the ability to model a sinusoidal flowrate transient. Input for the amplitude and frequency is required. If data is present in the transient data table, the sinusoidal transient is summed with the data in the transient data table.

A chopped sine wave takes the absolute value of the sine function. The end effect looks like doubling the frequency in the positive domain only, and having nothing in the negative domain.

A transient special condition also exist for assigned flow junctions. This is the No Reflections (Infinite Pipe) special condition.

For more information on transient data, including event transients, see Junction Transient Data.

Special Conditions

You can set a Special Condition for an Assigned Flow junction, which will turn the flow off and make it act like a Dead End during steady-state.

Special Features for Steady Flow

If the steady-state flow is zero at the junction, there may be occasions where you want the Assigned Flow junction to act like a pressure junction during the steady-state calculation. This would occur, for instance, if a known flowrate profile, initially zero, exists at the junction, and there are no other suitable pressure junctions in the system. In such a case, the pressure is assigned on the Optional tab.

Usually this feature would be used in conjunction with a Special Condition on the junction where its flow was turned off during steady-state.