1- Flow in Open Channel 2-14-15

DAA 2723 HYDRAULICS& HYDROLOGY DAA 2723 HYDRAULICS COURSE OUTCOMES (CO): CO1-Define types of channel and- Analyse and evaluate channel uniform flow and non-uniform transition flow CO2 -- Analysepipenetworkusingheaddistribution method and- Identifythetypeofpumps,theirselection criteria and performance evaluation. DAA 2723 HYDRAULICS By the end of 7th week students should be able to: 1. Define and identify types of channel and flow (CO1) 2. Define&analysetheuniformandnonuniformflow in open channels (CO1) 3. Identify&solvetherapidlyvariedflow(hydraulic jump) problems (CO1) 4. Define & apply the use of specific energy concepts in hydraulics (CO1) 5. Calculatewaterdistributioninpipelinesusingpipe network and head distributionmethod (C02) 6. Identifytypesofpumps,theirselectioncriteriaand performance evaluation (C02) DAA 2723-HYDRAULICS & HYDROLOGY FLOW INOPEN CHANNEL LEARNING OUTCOME -define&identifytypeofchannel& flow - Identify geometric characteristic of channels DAA 2723-HYDRAULICS & HYDROLOGY INTRODUCTION Open Channel A conduit in which a liquid flows with a free surface Open channel hydraulics The study of the physics of fluids flow in conveyances in which the following fluids forms a free surface and is driven by gravity Types of Channel TWO types:natural and artificial Natural open channel : rivers, creeks (have irregular cross section) Allchannelswhichhavebeendevelopedby naturalprocesses and have not been significant improved by humans Artificialopenchannel:humanconstruction- flumes and canals. Allchannelswhichhavebeendevelopedby human efforts Geometric Characteristics of Channels Parameter Symbol DefinitionDepth of flow y Depth from the bottom of channel to water surfaceDepth of section d Depth of flow, normal to water flowingStage z Distance from water surface to channel's bedUpper width T Width of water surfaceArea A Area of cross section normal to water flowingWetted parameter PHydraulics radius R Ratio of area to wetted parameter, R=A/PHydraulics depth D Ratio of area to upper width, D = A/Td = y cos uu =angle between slope of channel and channel's bedIfu too small, y ~ dNext Types of Flow Open channel flow can be classified into many types and described in various ways. The types of flow encountered in open channel are classified with respect to time, space, viscosity, density and gravity. Next Free Surface Essentially an interface between two fluids of different density An interface between the moving liquid and overlying fluid medium and will have constant pressure In the case of atmosphere - density of air is < density for liquid such as water.- pressure is constant. In the case of flowing liquid - the motion is usually caused by gravitational effects- the pressure distribution within the fluid is generally hydrostatic (flows are almost turbulent and unaffected by surface tension). Back Category of artificial open channel Prismatic: - has both a constant cross-sectional shape and bottom slope. -- Channels which do not meet this criteria are termed non prismatic. Canal:-the term canal refer to a rather long channels may be either unlined or lined with concrete, cement, grass, wood, bituminous materials or artificial membrane. Flume:- In practice, the term refers to a channels built above the ground surface to convey a flow across a depression.-The term flumes is also applied to laboratory channels constructed for basic and applied research. - Flumes are usually constructed of wood, metal, masonry or concrete.Chute & Drop:- A chute is a channel having a steep slope.- A drop channel also has a steep slope but is much shorter than a chute. Culvert:- A culvert flowing only partially full is an open channel primarily used to convey a flow under highways, railroad embankments or runways. Back River & Creek Natural Open Channel Back All natural channels generally have varying cross-sections and consequently are non prismatic. back Prismatic Rideau canals Welland canal Back Canals Flumes Back Chute & Drop Back Culvert Back The primary criteria of classification is the variation of the depth of flow y in time, t and space, x. Time a flow can be classified as being: Steady - which implies that the depth does not change with time (oy/ot = 0) Unsteady - which implies that the depth does change with time (oy/ot 0) Space a flow can be classified as being: Uniform if the depth of flow does not vary with distance (oy/ox = 0) Non uniform (varied flow) - if the depth varies with distance (oy/ox 0) Rapidly varied the depth of flow changes rapidly over a relatively short distance such as is the case with hydraulic jump Gradually varied the depth of flow changes rather slow with distance such as is the case of a reservoir behind the dam Next Time Space

Flow in Open Channel Steady Flow Uniform FlowNon Uniform Flow Rapidly varied FlowGradually Varied Flow Unsteady Flow Back Next The following classification is made according tothe change in flow depth with respect to time and space. Back Viscosity Depending on the ratio of the inertial forces to the viscous forces, a flow may be classified as laminar, transitional or turbulent The basis for this classification is a dimensionless parameter known as the Reynolds number Re= vL/u v = characteristic velocity of flow,often taken as the average velocity of flow L = characteristic length u = kinematics viscosity = / = dynamic viscosity = density In open channel flow, the characteristic length commonly used is the hydraulic radius, R which is the ratio of the flow area, A to the wetted perimeter, P. Re < 500 Laminar flow 5000 < Re 1, the flow is in supercritical state and the inertial forces are dominant. The denominator of the Froude number is the celerity of an elementary gravity wave in shallow water. Through theory of Mechanics of Wave; c = gy Where c = celerity g = gravity y~ d = the depth f flow which is a valueassumption if the channel is wide Next With this observation, the following interpretation can be applied to the subcritical and supercritical of flow: Subcritical flow, F1,- velocity of flow is > celerity of an elementary gravity wave.Therefore, such a wave can propagate upstream against the flow and the upstream areas of the channel are not in hydraulic communication with the downstream areas. Back COURSE OUTCOME (CO1) -define the types of channel flow DAA 2723-HYDRAULICS & HYDROLOGY