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Needle Valve - Simulate hydraulic needle valve

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Flow Control Valves

Description

The Needle Valve block models a variable orifice created by a conical needle and a round sharp-edged orifice in thin material.

The flow rate through the valve is proportional to the valve opening and to the pressure differential across the valve. The model accounts for the laminar and turbulent flow regimes by monitoring the Reynolds number (Re) and comparing its value with the critical Reynolds number (Re_cr). The flow rate is determined according to the following equations:

where

`q`	Flow rate
`p`	Pressure differential
`p_A,p_B`	Gauge pressures at the block terminals
`C_D`	Flow discharge coefficient
`A(h)`	Instantaneous orifice passage area
`x₀`	Initial opening
`x`	Needle displacement from initial position
`h`	Valve opening
`h_max`	Maximum needle stroke
`d_s`	Orifice diameter
α	Needle angle
ρ	Fluid density
`D_H`	Valve instantaneous hydraulic diameter
ν	Fluid kinematic viscosity
`A_leak`	Closed valve leakage area
`A_max`	Maximum valve open area

The block positive direction is from port A to port B. This means that the flow rate is positive if it flows from A to B and the pressure differential is determined as . Positive signal at the physical signal port S opens the valve.

Basic Assumptions and Limitations

The model is based on the following assumptions:

Fluid inertia is not taken into account.
The transition between laminar and turbulent regimes is assumed to be sharp and taking place exactly at Re=Re_cr.
The flow passage area is assumed to be equal to the frustum side surface area.

Dialog Box and Parameters

Valve orifice diameter: The diameter of the orifice of the valve. The default value is 0.005 m.
Needle cone angle: The angle of the valve conical needle. The parameter value must be in the range between 0 and 180 degrees. The default value is 90 degrees.
Initial opening: The initial opening of the valve. You can specify both positive and negative values. The default value is 0.
Flow discharge coefficient: Semi-empirical parameter for valve capacity characterization. Its value depends on the geometrical properties of the orifice, and usually is provided in textbooks or manufacturer data sheets. The default value is 0.65.
Critical Reynolds number: The maximum Reynolds number for laminar flow. The transition from laminar to turbulent regime is supposed to take place when the Reynolds number reaches this value. The value of the parameter depends on orifice geometrical profile, and the recommendations on the parameter value can be found in hydraulic textbooks. The default value is 10.
Leakage area: The total area of possible leaks in the completely closed valve. The main purpose of the parameter is to maintain numerical integrity of the circuit by preventing a portion of the system from getting isolated after the valve is completely closed. An isolated or "hanging" part of the system could affect computational efficiency and even cause failure of computation. Extreme caution should be exercised if the parameter is set to 0. The default value is 1e-12 m^2.

Global Parameters

Fluid density: The parameter is determined by the type of working fluid selected for the system under design. Use the Hydraulic Fluid block or the Custom Hydraulic Fluid block to specify the fluid properties.
Fluid kinematic viscosity: The parameter is determined by the type of working fluid selected for the system under design. Use the Hydraulic Fluid block or the Custom Hydraulic Fluid block to specify the fluid properties.

Ports

The block has the following ports:

A: Hydraulic conserving port associated with the valve inlet.
B: Hydraulic conserving port associated with the valve outlet.
S: Physical signal port to control spool displacement.