Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D5614-94 – Standard Test Method Technical Guide
This test method, designated ASTM D5614-94, provides a standardized approach for measuring volumetric flow rate in open channels using broad-crested weirs. It addresses two weir configurations: square (sharp) upstream corner and well-rounded upstream corner, as defined in the scope.
📐 Weir Types and Specifications
The standard specifies horizontal broad-crested weirs with two types of upstream corners. The crest is the horizontal plane surface over which flow occurs. Proper geometry ensures accurate critical flow conditions.
| 🟦 Weir Type | 📏 Upstream Corner Shape | 🎯 Key Characteristic |
|---|---|---|
| Square Corner | Sharp, 90-degree edge | Standard configuration |
| Rounded Corner | Well-rounded profile | Reduced energy loss |
⚙️ Test Procedure and Key Parameters
Flow measurement relies on establishing critical flow over the weir, where the Froude number is unity. The head, defined as the depth of water above the crest, is measured upstream. The boundary layer displacement thickness affects the flow profile and must be accounted for.
⚠️ Ensure the weir is free from obstructions and the nappe is well-ventilated to prevent backwater effects.
| 🔢 Parameter | 📐 Definition (from Standard) | ⚡ Condition |
|---|---|---|
| Froude Number | Ratio of inertial to gravity forces | Unity at critical flow |
| Head (Measuring Head) | Depth of flow above weir crest at upstream location | Used for total energy head calculation |
| Boundary Layer Displacement | Distance streamlines displaced due to viscous friction | Affects discharge coefficient |
📊 Critical Flow and Head Measurement
Critical flow occurs when the specific energy is minimized, with the Froude number equal to 1. The total energy head combines depth and velocity head. The standard references ISO 3846 and ISO 4374 for rectangular and round-nose broad-crested weirs, respectively.
✅ For accurate head measurement, use stilling wells or stilling basins to average out wave effects, as per ISO 4373.
❓ Frequently Asked Questions
🔍 What are the two configurations of broad-crested weirs in D5614-94?
The standard covers weirs with square (sharp) upstream corners and those with well-rounded upstream corners.
The standard covers weirs with square (sharp) upstream corners and those with well-rounded upstream corners.
💡 How is the measuring head defined?
The measuring head is the depth of flow above the weir crest measured at an appropriate upstream location.
The measuring head is the depth of flow above the weir crest measured at an appropriate upstream location.
⚡ What is critical flow in this context?
Critical flow is when the Froude number is unity, indicating minimum energy for a given flow rate.
Critical flow is when the Froude number is unity, indicating minimum energy for a given flow rate.
📌 Which ISO standards are referenced?
ISO 3846-1989 for rectangular broad-crested weirs and ISO 4374-1990 for round-nose horizontal crest weirs.
ISO 3846-1989 for rectangular broad-crested weirs and ISO 4374-1990 for round-nose horizontal crest weirs.