1、Designation: D5242 92 (Reapproved 2013)Standard Test Method forOpen-Channel Flow Measurement of Water with Thin-PlateWeirs1This standard is issued under the fixed designation D5242; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, t
2、he year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers measurement of the volumetricflowrate of water and wastewater in channels with thin
3、-plateweirs. Information related to this test method can be found inRantz (1)2and Ackers (2).1.2 The values stated in inch-pound units are to be regardedas the standard. The SI units given in parentheses are forinformation only.1.3 This standard does not purport to address all of thesafety concerns,
4、 if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3D1129 Terminology Relating to WaterD2777 Pra
5、ctice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3858 Test Method for Open-Channel Flow Measurementof Water by Velocity-Area Method2.2 ISO Standards:4ISO 1438 Flow Measurement in Open Channels Using Weirsand Venturi FlumesPart 1: Thin-Plate WeirsISO 5
6、55 Liquid Flow Measurement in Open Channels,Delusion Methods for Measurement of Steady Flow-Constant Rate Injection Method3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this test method, referto Terminology D1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 crestthe
7、 bottom of the overflow section or notch ofa rectangular weir.3.2.2 headthe height of a liquid above a specified point,for example, the weir crest.3.2.3 hydraulic jumpan abrupt transition from supercriti-cal flow to subcritical or tranquil flow.3.2.4 nappethe curved sheet or jet of water overfalling
8、 theweir.3.2.5 notchthe overflow section of a triangular weir or ofa rectangular weir with side contractions.3.2.6 primary instrumentthe device (in this case the weir)that creates a hydrodynamic condition that can be sensed by thesecondary instrument.3.2.7 scow floatan in-stream float for depth sens
9、ing,usually mounted on a hinged cantilever.3.2.8 secondary instrumentin this case, a device thatmeasures the depth of flow (referenced to the crest) at anappropriate location upstream of the weir plate. The secondaryinstrument may also convert the measured depth to an indi-cated flowrate.3.2.9 still
10、ing wella small free-surface reservoir connectedthrough a constricted channel to the approach channel up-stream of the weir so that a depth (head) measurement can bemade under quiescent conditions.3.2.10 subcritical flowopen channel flow in which theaverage velocity is less than the square root of t
11、he product ofthe average depth and the acceleration due to gravity; some-times called tranquil flow.3.2.11 submergencea condition where the water level onthe downstream side of the weir is at the same or at a higherelevation than the weir crest; depending on the percent ofsubmergence the flow over t
12、he weir and hence the head-discharge relation may be altered.3.2.12 supercritical flowopen channel flow in which theaverage velocity exceeds the square root of the product of theaverage depth and the acceleration due to gravity.1This test method is under the jurisdiction of ASTM Committee D19 on Wat
13、erand is the direct responsibility of Subcommittee D19.07 on Sediments,Geomorphology, and Open-Channel Flow.Current edition approved Jan. 1, 2013. Published January 2013. Originallyapproved in 1992. Last previous edition approved in 2007 as D5242 92 (2007).DOI: 10.1520/D5242-92R13.2The boldface numb
14、ers in parentheses refer to a list of references at the end ofthe text.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe AST
15、M website.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.13 tailwaterthe water level immediately downs
16、treamof the weir.4. Summary of Test Method4.1 Thin-plate weirs are overflow structures of specifiedgeometries for which the volumetric flowrate is a uniquefunction of a single measured depth (head) above the weir crestor vertex, the other factors in the head-discharge relationhaving been experimenta
17、lly or analytically determined asfunctions of the shape of the overflow section and approachchannel geometry.5. Significance and Use5.1 Thin-plate weirs are reliable and simple devices thathave the potential for highly accurate flow measurements. Withproper selection of the shape of the overflow sec
18、tion a widerange of discharges can be covered; the recommendations inthis test method are based on experiments with flowrates fromabout 0.008 ft3/s (0.00023 m3/s) to about 50 ft3/s (1.4 m3/s).5.2 Thin-plate weirs are particularly suitable for use inwater and wastewater without significant amounts of
19、 solids andin locations where a head loss is affordable.6. Interferences6.1 Because of the reduced velocities in the backwaterupstream of the weir, solids normally transported by the flowwill tend to deposit and ultimately affect the approach condi-tions.6.2 Weirs are applicable only to open channel
20、 flow andbecome inoperative under pressurized-conduit conditions.7. Apparatus7.1 A weir measuring system consists of the weir plate andits immediate channel (the primary) and a depth (head)measuring device (the secondary). The secondary device canrange from a simple scale for manual readings to an i
21、nstrumentthat continuously senses the depth, converts it to a flowrate,and displays or transmits a readout or record of the instanta-neous flowrate or totalized flow, or both.7.2 Thin-Plate Weir:7.2.1 ShapesThe thin-plate weir provides a preciselyshaped overflow section symmetrically located in a (u
22、sually)rectangular approach section, as in Fig. 1 and Fig. 2. Althoughinformation is available in the literature (3) on a variety ofoverflow-section or notch shapes (for example, rectangular,triangular, trapezoidal, circular) only the rectangular and trian-gular shapes are considered to have a data
23、base sufficient forpromulgation as a standard method.7.2.2 Weir Plate:7.2.2.1 The plate thickness in the direction of flow must befrom 0.03 in 0.08 in. (about 1 to 2 mm); the lower limit isprescribed to minimize potential damage, and the upper limit isrequired to help avoid nappe clinging. See 7.2.5
24、.4 and 7.2.6.3for plates thicker than 0.08 in. (2 mm). The plate must befabricated of smooth metal or other material of equivalentsmoothness and sturdiness. Upstream corners of the overflowsection must be sharp and burr-free, and the edges must be flat,smooth, and perpendicular to the weir face.7.2.
25、2.2 The plane of the weir plate must be vertical andperpendicular to the channel walls. The overflow section mustbe laterally symmetrical and its bisector must be vertical andFIG. 1 Rectangular WeirFIG. 2 Crest-Length Adjustment, LD5242 92 (2013)2located at the lateral midpoint of the approach chann
26、el. If themetal plate containing the overfall section does not form theentire weir, it must be mounted on the remainder of thebulkhead so that the upstream face of the weir is flush andsmooth. (This requirement may be relaxed if the metal plate islarge enough in itself to form full contractions. See
27、 7.2.3.) Theweir structure must be firmly mounted in the channel so thatthere is no leakage around it.7.2.2.3 Additional plate requirements specific to rectangularand triangular weirs are given in 7.2.5.4 and 7.2.6.3.7.2.3 Weir ContractionsWhen the sidewalls and bottom ofthe approach channel are far
28、 enough from the edges of thenotch for the contraction of the nappe to be unaffected by thoseboundaries, the weir is termed “fully contracted.” With lesserdistances to the bottom or sidewalls, or both, the weir is“partially contracted.” Contraction requirements specific torectangular and triangular
29、weirs are given in 7.2.5.3, 7.2.5.6,7.2.6.2, and 7.2.6.5.7.2.4 Head Measurement LocationThe head on the weir,H, is measured as a depth above the elevation of the crest orvertex of the notch. This measurement should be made at adistance upstream of the weir equal to 4 Hmaxto 5Hmax, whereHmaxis the ma
30、ximum head on the weir. In some cases a stillingwell may be desirable or necessary. See 7.5.7.2.5 Rectangular Weirs:7.2.5.1 The rectangular overflow section can have either fullor partial contractions (7.2.3) or the side contractions may besuppressed (7.2.5.2).7.2.5.2 Suppressed Weirs When there are
31、 no side contrac-tions and the weir crest extends across the channel, the weir istermed “full width” or “suppressed.” In this case the approachchannel must be rectangular (see also 7.3.4) and the channelwalls must extend at least 0.3H downstream of the weir plate.7.2.5.3 Contracted Rectangular Weirs
32、 The conditions forfull contraction are as follows:H/P # 0.5H/L # 0.50.25 ft (0.08 m) # H # 2.0 ft (0.6 m)L $ 1.0 ft (0.3 m)P $ 1.0 ft (0.3 m)( B L )/2 $2Hwhere H is the measured head, P is the crest height above thebottom of the channel, L is the crest length, and B is thechannel width. The partial
33、 contraction conditions covered bythis test method are given in 7.2.5.6.7.2.5.4 Weir PlateThe requirements of this section are inaddition to those of 7.2.2. If the plate is thicker than 0.08 in. (2mm) the downstream excess at the edges of the overflowsection must be beveled at an angle of at least 4
34、5 as shown inFig. 1. If there are side contractions, all of the edge require-ments of this test method pertain to the sides as well as thecrest. The sides must be exactly perpendicular to the crest; andthe crest must be level, preferably to within a transverse slopeof 0.001.7.2.5.5 Discharge Relatio
35、nsThe flowrate, Q, over a rect-angular weir that conforms to all requirements of 7.2 as well asthe approach conditions in 7.3 is determined from theKindsvater-Carter equation (4):Q 5 2/3!2g!1/2CeLeHe!3/2(1)where g is the acceleration due to gravity in compatibleunits, Heand Leare the effective head
36、and effective crest lengthrespectively, and Ceis a discharge coefficient. The effectivehead, He, is related to the measured head, H, by:He5 H1Hwhere H is an experimentally determined adjustment forthe effects of viscosity and surface tension valid for water atordinary temperatures (about 4 to 30C);
37、its value is constant at0.003 ft (0.001 m). The effective crest length, Le, is related tothe measured length, L, by:Le5 L1Lwhere the adjustment, L, is a function of the crest length-to-channel width ratio, L/B. Experimentally determined valuesof L for water at ordinary temperatures are given in Fig.
38、 3.The discharge coefficient, Ce, is given in Fig. 4 as a functionof L/B and the head-to-crest height ratio, H/P.7.2.5.6 Limits of ApplicationThe discharge relations givenin 7.2.5.5 are applicable for these conditions:H/P # 2H $ 0.1 ft (0.03 m)L $ 0.5 ft (0.15 m)P $ 0.3 ft (0.1 m)Although in princip
39、le Eq 1 could be applied to very largeweirs, the experiments on which it is based included crestlengths up to about 4 ft (1.2 m) and heads up to about 2 ft (0.6m); it is recommended that these values not be significantlyexceeded.7.2.5.7 Aeration RequirementsIn order to avoid nappeclinging and mainta
40、in proper aeration of the nappe, thetailwater level should always be at least 0.2 ft (0.06 m) belowthe crest. In addition, in the case of suppressed weirs, aerationmust be provided externally; this can be done with sidewallvents, for example. The user must measure the pressure in theair pocket to es
41、tablish that it is sufficiently close to atmosphericfor the flow to be unaffected (see 11.7.2).7.2.6 Triangular Weirs:7.2.6.1 ShapeThe overflow section of a triangular weir isan isosceles triangle oriented with the vertex downward.FIG. 3 Discharge Coefficient, Ce, for Rectangular WeirsD5242 92 (2013
42、)3Experimental results are available for notch angles, ,of20to100. However, the most commonly used weirs are 90 (tan/2 = 1), 53.13 (tan /2 = 0.5) and 28.07 (tan /2 = 0.25). SeeFig. 2.7.2.6.2 Contractions The conditions for full contractionof triangular weirs are as follows:H/P # 0.4H/B # 0.2P $ 1.5
43、ft (0.45 m)B $ 3.0 ft (0.9 m)0.15 ft (0.05 m) # H # 1.25 ft (0.38 m)The conditions for partial contraction covered by this testmethod are listed in 7.2.6.5.7.2.6.3 Weir PlateIf the plate is thicker than 0.08 in. (2mm) the downstream excess at the notch must be beveled at anangle of at least 60 (Fig.
44、 2). This requirement is in addition tothose of 7.2.2.7.2.6.4 Discharge RelationsThe flowrate over a triangularweir that conforms to all requirements of 7.2.3 as well as theapproach conditions in 7.3 is determined from the following:Q 5 8/15!2g!1/2Cettan/2!Het!5/2(2)where Cetand Hetare the discharge
45、 coefficient and effectivehead respectively. Hetis given by:Het5 H1Htwhere Htis an adjustment for the combined effects ofviscosity and surface tension for water at ordinary temperatures(4 to 30C) and is given as a function of notch angle in Fig. 5.The discharge coefficient is given in Fig. 6 as a fu
46、nction of thenotch angle for fully contracted weirs only. For partiallycontracted weirs the data base is considered adequate for 90notches only and these discharge coefficients are shown in Fig.7.7.2.6.5 Limits of ApplicationFor 90 notches only, thedischarge relations given in 7.2.6.4 are valid for
47、these partiallycontracted conditions:H/P # 1.2H/B # 0.4P $ 0.3 ft (0.1 m)B $ 2ft(0.6m)0.15 ft (0.05 m) # H # 2ft(0.6m)For other angles between 20 and 100 the discharge relationsare valid only for full contractions (see 7.2.6.2).7.2.6.6 Aeration RequirementsIn order to avoid nappeclinging and maintai
48、n proper aeration of the nappe, thetailwater level should always be at least 0.2 ft (0.05 m) belowthe vertex of the triangular notch.7.3 Approach Channel:7.3.1 Weirs can be sensitive to the quality of the approachflow. Therefore this flow should be tranquil and uniformlydistributed across the channe
49、l in order to closely approximatethe conditions of the experiments from which the dischargerelations were developed. For this purpose, uniform velocitydistribution can be defined as that associated with fullydeveloped flow in a long, straight, moderately smooth channel.Unfortunately there are no universally accepted quantitativeguidelines for implementing these recommendations. Onestandard (5) recommends a straight approach length of tenchannel widths when the weir length is greater than half thechannel width. However,
