This is an excel sheet that calculates the specific energy curve and its components in open channel. Natural channels display a much wider range of roughness values than artificial channels. The minimum specific energy is also called the critical energy. Examine specific energy in nonrectangular channels. Specific energy diagram showing critical and alternate depths 1. Minimum specific energy and critical flow conditions in.
Chapter 2 hydraulics of selected hydraulic structures. Open channel flow example using specific energy curve. For simplicity, the following specific energy often referred to as specific head. Dimensionless specific energy diagrams for open channel flow. In open channel hydraulics, critical depth is the depth of flow for a given discharge where the specific energy is at a minimum. Typical examples include rivers and canals, drainage channels, gutters, water rides at amusement parks or sewerage. Flows for the lower part of the specific energy diagram are supercritical fr1. Fundamentals of open channel flow 1st edition glenn e. In a closed conduit there can be a pressure gradient that drives the flow.
An open channel has atmospheric pressure at the surface. Whats the purpose of developing the term of specific energy for open channel flow. Bakhmeteff 1912, and critical flow conditions are observed at the weir crest chanson 2006, unless the crest is drowned. For any given flow an obstruction such as a sluice gate, a step in the channel bottom, or a constriction might require more energy than the flow originally possesses, and thus a transient condition is set up where the unit discharge is temporarily reduced as. Critical depth and specific energy curve author humberto avilaphd 3 or, it can be also expressed as following by using qqb, 3 2 g q yc 5 the minimum specific energy for rectangular channel is given by, ec yc 2 3 6 4. The specific energy es of a liquid in an open channel is the total mechanical energy expressed as a head relative to the bottom of the channel. Specific energy, which is the key to even the most complex. Energy, specific energy, and gradually varied flow. Open channel flow florida international university. In an open channel flow froude number is defined as. Critical depth one useful parameter in channel flow is the specific energy e, where y is the local water depth. The specific energy of an open channel flow indicates the nount of kinetic and potential energy per unit weight of the liquid at a specific location. The normal depth is used to design artificial channels in a steady, uniform flow. Complete the specific energy diagram below with the appropriate values.
Visualization of specific energy for open channel flow in three. In open channel flow, specific energy e is the energy length, or head, relative to the channel bottom. If the water depth is shallower than the critical depth, then the flow is supercritical. The specific energy es of a liquid in an open channel is the total mechanical energy expressed. It shows graphically the effect of changing specific discharge on the specific energy curve. In open channel flow the driving force that is the force causing the motion is the component of gravity along the channel bottom.
Apr 17, 2015 fundamentals of open channel flow outlines current theory along with clear and fully solved examples that illustrate the concepts and are geared to a first course in open channel flow. The specific energy equation is draganddrop the appropriate labels to their respective targets. Minimum specific energy and critical flow conditions in open channels. The specific energy diagram is specific to the unit discharge for a given flow rate. Hydraulics of minimum energ loss mel culverts and bridge.
Depthaveraged specific energy in openchannel flow and. As the depth of flow increases, the static energy increases and the kinetic energy decreases 3. Describe this flow in terms of the specific energy diagram. Pdf chapter openchannel flow solutions manual for. In open channels and for a given specific energy, maximum flow rate is achieved for critical flow conditions belanger 1828. It also allows the verification of the chezy equation and mannings friction factor. Introduction bernoulli equation applied to the free surface in an open channel see figure 1. Fundamentals of fluid mechanics chapter 10 flow in open. Department of bioindustrial mechatronics engineering. The critical depth and the corresponding minimum specific energy c. If one plots the depth of flow as ordinate against the specific energy for a constant q, the energy diagram is obtained, which is a very useful curve in open channel.
It is the responsibility of the designer to be knowledgeable of open channel. At lower limb, cr of the specific energy curve is the supercritical flow region. Definition sketch of the energy diagram for openchannel flow. The open channel flow calculator select channel type. Some characteristics of open channel transition flow. Openchannel flows are characterized by the presence. Hydraulics 3 answers openchannel flow notes 7 dr david apsley section 2. For frictionless and horizontal channel specific energy will be constant. In addition studies of specific energy depth relationships, the effect of various. Pdf chapter openchannel flow solutions manual for fluid.
Open channel flow involves the flows of a liquid in a channel or conduit that is not. Thus, specific energy is the energy at a crosssection of an open channel flow with respect to the channel bed. Combining the two relationships specific energy diagram figure 2. Open channel flow is a flow which has a free surface and flows due to gravity. Schematic representation of alternate and critical depths locations and the flow regimes on the specific energy curve. I understand specific energy is a component of the total energy by not taking account of the vertical distance from vertical datum to channel bottom. Froehlich abstract the three basic principles of openchannel flow analysis the conserva tion of mass, energy, and momentum are derived, explained, and applied to solve problems of openchannel flow. Specific energy is expressed in terms of kinetic energy, and potential energy, and internal energy. It is a summation of the velocity head and the depth of flow at a given cross. Open channel flow example using specific energy curve fluid. Flow cannot occur with specific energy less than the. In an open channel flow, there are three types of flow. Experimental procedure the specific energy curves will be determined by using a sluice gate. What is the slope of the specific energy equation at minimum energy.
Specific energy is the total head with respect to the channel bottom. Specific energy and alternate depths of flow the specific energy diagram let us consider wide rectangular channels. Chapter open channel flow solutions manual for fluid mechanics. Definition sketch of the energy diagram for openchannel flow 43 62. State whether the flow is subcritical or supercritical d. Pipes not flowing full also fall into the category of open channel flow in open channels, the flow is driven by the slope of the channel rather than the pressure. To summarize, to sustain any specified flow rate per unit width qa, or q of an ideal fluid in an open channel, the specific energy of the fluid must exceed a minimum value, emin. A depthaveraged form of the bernoulli equation for ideal fluid flows introduces correction. The term h is called the specific head, and is the height of the total head above the channel. Minimum specific energy and critical flow conditions in open. Schematic and flow depth specific energy diagram for a hydraulic jump specific energy decreases. As a result, on the portion of the specific energy curve where v v c, the flow is supercritical, and on the portion where v flow is subcritical. The specific energy diagram is used to determine the most likely water depth. In a uniform openchannel flow, for which both kinetic energy and potential energy are the same at every cross section but potential energy decreases downstream, the head loss is simply the rate of decrease of elevation head downstream, or in other words the slope of the water surface and bed surface, which is then also equal to the energy slope.
Ho, also called the specific energy, is simply the head i. The bernoulli equation, which originates from a control volume analysis, is used to describe specific energy relationships in fluid dynamics. For any given flow an obstruction such as a sluice gate, a step in the channel bottom, or a constriction might require more energy than the flow originally possesses, and thus a transient condition is set up where the unit discharge is temporarily reduced as the flow backs up and gains energy. Sep 12, 2014 specific energy for a channel with constant width b, plot of es vs. It highlights the practical computational tools students can use to solve problems, such as spreadsheet applications and the hecras program. Use the froude number, critical depth, and flow velocity to. Pipes not flowing full also fall into the category of open channel flow in open channels, the flow is driven by the. Adaptation of the bernoulli equation to openchannel flows under the. The above diagram is only applicable for a specific flowrate and cross section 2.
Only if an openchannel flow can somehow be adjusted to be strictly uniform, in the sense that the water surface is planar and the flow depth is the same at all cross sections along the flow figure 55, can the effect of gravity in shaping the flow be ignored. Basic hydraulic principles of openchannel flow by harvey e. The total energy head specific energy for a cross section is given by. Dimensionless specific energy diagrams for openchannel flow. Specific energy this plot is very useful easy to see breakdown of es into pressure y and dynamic v22g head es as y 0 es y for large y es reaches a minimum called the critical point. In open channels, the relationship between the specific energy and the flow depth exhibits a minimum, and the corresponding flow conditions are called critical flow conditions. Some concepts that are unique to open channels for example, specific energy and channel. The variation of specific energy with depth at a constant discharge shows a minimum. Introduction when the surface of flow is open to atmosphere, in other terms when there is only atmospheric pressure on the surface, the flow is named as open channel flow.
Energy, specific energy, and gradually varied flow 10. Energydepth relationship in a rectangular channel wikipedia. Diagram illustrating typical flow through a bridge. What is special about these quantities in critical conditions. The total discharge divided by the channel width valid only for a rectangular channel. If the datum coincides with the channel bed at the section, the resulting expression is known as specific energy and is denoted as e. The governing force for the open channel flow is the gravitational force component along the channel slope. If water depth is deeper than the critical depth y c, then the flow is subcritical. Measurement of energy relative to the bottom of the channel. Specific energy e in a channel section is the sum of the elevation head and velocity head, measured with respect to the channel bottom.
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