## Hydraulic orifice definition

@HYDRAULIC_ORIFICE_DEFINITION {
@HYDRAULIC_ORIFICE_NAME {HydOrfcName} {
@HYDRAULIC_DEVICE_MODEL_NAME {HydModl}
@HYDRAULIC_CHAMBER_NAME {HydChmb0Name, HydChmb1Name}
@FUNCTION_1D_NAME {Fun1DName}
@ORIFICE_ENTRANCE_PRESSURE {pEnt}
@ORIFICE_CIRCUIT_PRESSURE {pCir}
}
}

### Introduction

##### Figure 1. Configuration of the hydraulic orifice.

The hydraulic orifice, shown in fig. 1, allows the flow of hydraulic fluid through an orifice of sectional area Aorf and is associated with hydraulic device model, HydModl. The orifice is connected to two hydraulic chambers, HydChmb0Name and HydChmb1Name, respectively, with pressures p0 and p1, respectively. A pressure differential, Δp = p0 - p1, will drive a flow rate Qorf across the orifice; the positive direction of this flow is indicated on the figure.

Pressures p0 and p1 are, in general, the pressures in chambers HydChmb0Name and HydChmb1Name, respectively. For the linear hydraulic actuator, the orifice connects a chamber to an oil supply that can be at the entrance pressure pEnt or at the circuit pressure pCir.

The description and formulation of the hydraulic orifice and elements describes the relationships among these variables.

### Computation of the orifice flow

The flow through the orifice, Qorf, is related to the pressure drop, Δp, across the orifice by means of 1D function, Fun1DName. The following formula is used,
Qorf = F(|Δp|)   sign(Δp),
where a 1D function, F = F(|Δp|), defines the relationship between the flow and the pressure drop across the orifice through a Chebyshev expansion. The term sign(Δp) enforces the sign convention.

Typically, the flow-pressure drop relationship is determined experimentally and a Chebyshev approximation is used to fit the data. In the absence of experimental data, the following formula can be used
Qorf = Aorf Cd√(2|Δp|/ρ)  sign(Δp),
where Aorf is the orifice throttling area and ρ the mass density of the hydraulic fluid. For turbulent flow conditions, the theoretical value of the discharge coefficient is Cd = 0.611. This empirical formula corresponds to a Chebyshev expansion with a single term, c1 = Aorf Cd√(2/ρ).

### NOTES

1. It is possible to attach comments to the definition of the object; these comments have no effect on its definition.