4.37. Venturi

4.37.1. Venturi (class)

Fig. 4.37.1 Venturi for discharge measurement in open channel

Fall type

type label	description	active
Venturi_open	Venturi for discharge measurement in an open channel, according to norm ISO 1438-1975	no

4.37.1.1. Mathematical model

The VENTURI can be used for a discharge measurement in an open channel by measuring the resistance in the throat of the venturi. The equations which are used to model the venturi are taken from the ISO 1438-1975 norm.

A venturi is described by:

(4.37.1)\[Q=\left(\frac{2}{3}\right)^{\frac{3}{2}} C_{v} C_{e} \sqrt{g} b h_{v}^{\frac{3}{2}} \quad \text { or } \quad h_{v}=\left(\frac{Q}{\left(\frac{2}{3}\right)^{\frac{3}{2}} C_{v} C_{e} \sqrt{g} b} \end{array}\right)^{\frac{2}{3}}\]

in which the constants C_e and C_v are given by:

(4.37.2)\[C_{e}=\left(\frac{b}{b+0,004 l}\right)^{1,5}\left(\frac{h_{1}-0,003 l}{h_{1}}\right)^{1,5}\]

with:

Symbol	Unit	Description
Q	[m3/s]	discharge
Cv	[-]	Jameson’s velocity coefficient
Ce	[-]	Horner’s discharge coefficient
g	[m2/s]	Gravitational acceleration
b	[m]	Throat width venturi
hv	[m]	Fluid level in the venturi throat relative to the bottom of the channel
h1	[m]	Upstream water level
L	[m]	Throat length
B	[m]	Width of upstream channel

NB: This component can not be used for venturi’s without a flat bottom. The use of the venturi component is limited to venturi’s in which the throat is formed by a narrowing of the channel.

Fig. 4.37.2 Side view Venturi

Fig. 4.37.3 top view Venturi

4.37.2. Venturi_open

4.37.2.1. Hydraulic specifications

Description	Input	Unit	Range	default	Remarks
Length venturi throat	Real	[-]	(0, 1]
Width venturi	Real	[-]	(0, 1]
Width upstream channel	Real	[m]	(0; 100]
Height bottom	Real	[m]	(-100; 10000]		Relative to reference point

See also: “Mathematical model” on page 458.

4.37.2.2. Component specific output

Description	Unit	Remarks
Water depth upstream	[m]
Cv coefficient Jameson	[-]
Ce coefficient Horner	[-]

4.37.2.3. H-actions

None

4.37.2.4. Component messages

Message	explanation
Error: width ratio outside Cv range	Ratio width throat/channel is outside the range given in the ISO norm [0.1-0.7]
Warning: downstream level above upstream level	Downstream head is larger than upstream head (H2>H1), discharge in opposite direction
Warning: Downstream level above 60 % upstream level	Depth is larger than 60% of upstream water level