General Headloss
  • 15 Aug 2022
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General Headloss

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The General Headloss unit models a generalised channel head loss and can operate either in upstream mode (where flow velocities are obtained from the node upstream of the headloss) or in downstream mode (where flow velocities are obtained from the downstream connected node).

Data

Field in Data Entry Form

Description

Name in Datafile

Upstream Node

Upstream node label

Label1

Downstream Node

Downstream node label

Label2

Remote Node

Remote node label

Label3

 Loss Coefficient

Head loss coefficient

K

Reverse Flow Mode

Reverse Flow Mode; keyword ZERO (for zero head loss) or CALCULATED (for calculated head loss)

rfmode

Theory and Guidance

The General Headloss unit models a generalised channel head loss. The General Headloss can operate either in upstream mode (where flow velocities are obtained from the node upstream of the headloss) or in downstream mode (where flow velocities are obtained from the downstream connected node). When in upstream control the General Headloss must be placed immediately downstream of a channel section (for instance a River Section or Conduit type unit). Similarly, when in downstream control, the link must be placed immediately upstream of a River Section or Conduit type node. If these conditions are not rue, you must make use of the Remote Node facility.

The Remote Node will only be required when there is no channel node in the direction indicated by the "Flow Velocities Obtained From" field. If you set the Remote Node field to point to a River Section or Conduit type node, Flood Modeller will obtain the upstream or downstream flow velocities it requires from this control node.

The Reverse Flow Mode parameter determines which equation is used in reverse flow. If it set to Calculated, the headloss will use the same equation as for mode 1, but with h1 and h2 reversed. If it is set to Zero then the headloss imposed under reverse flow conditions will be zero. You will always be informed at the start and finish of reverse flow conditions for this unit.

The General Headloss is identical to the Culvert Bend.

Equations

Mode 1 - Positive Flow

Condition

Q ³ 0

Equation

GeneralHeadlossEqn

(1)

where:

K = Head loss coefficient

V = Channel flow velocity (derived from the upstream channel in upstream mode, and the downstream channel in downstream mode)

g =Acceleration due to gravity

Mode 2 - Reverse Flow

Condition

Q < 0

Equation

As for Mode 1.

General

The unit state for this unit is the current head loss coefficient.

Datafile Format

Line 1 - keyword LOSS''

Line 2 - Label1, Label2, [Label3]

Line 3 - Keyword UPSTREAM' or DOWNSTREAM'

Line 4 - K, rfmode

RiverNodesimagesHeadlossData.gif


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