Open Channel Flow: Supercritical and Non-uniform Flow

Many examples of open channel flow can be approximated as uniform flow allowing the Manning equation to be used. Non-uniform flow calculations are needed, however, in some open channel flow situations, where the flow is clearly non-uniform. The concepts of supercritical, subcritical and critical flow, and calculations related to those three regimes of flow, are needed for non-uniform open channel flow analysis and calculations. Hence, in this course, the parameter called specific energy are first used to introduce the concepts of critical, subcritical, and supercritical flow. Various calculations related to critical, subcritical and supercritical flow conditions are presented, including hydraulic jump calculations. The thirteen possible types of gradually varied non-uniform flow surface profiles are then be presented and discussed. Also, the procedure and equations for step-wise calculation of gradually varied non-uniform surface profiles are presented and illustrated with examples.

Topics: At the conclusion of this course, the student will: Be able to determine the critical depth for a specified volumetric flow rate through a rectangular channel of specified bottom width. Be able to determine the critical slope for a specified volumetric flow rate through an open channel of specified shape, size, & Manning roughness coefficient, with known critical depth. Be able to determine whether a specified volumetric flow rate through an open channel of given shape & size, with known depth of flow will be critical, subcritical or supercritical flow. Be able to calculate the depth of flow after a hydraulic jump if given the depth before the hydraulic jump, the volumetric flow rate and the shape and dimensions of the open channel. Be able to identify which type of surface profile (e.g. M1, M2, M3, S1, S2, S3, etc.) is present in a specified gradually varied flow situation. Be able to carry out a stepwise calculation of the surface profile for a specified, gradually varied, non-uniform open channel flow. Topics Covered in this Course Specific Energy as an Introduction to Supercritical, Subcritical and Critical Flow The Froude Number for Rectangular Channels The Froude Number for Non-rectangular Channels Calculation of Critical Slope The Hydraulic Jump Gradually Varied Open Channel Flow Gradually Varied Flow Surface Profile Classifications Gradually Varied Flow Surface Profiles by Stepwise Calculations Publication Source: Harlan H. Bengtson, PhD, PE