ASTM D5242-1992(2007) Standard Test Method for Open-Channel Flow Measurement of Water with Thin-Plate Weirs《有薄板堰水的明渠流量测量的试验方法》.pdf

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1、Designation: D 5242 92 (Reapproved 2007)Standard Test Method forOpen-Channel Flow Measurement of Water with Thin-PlateWeirs1This standard is issued under the fixed designation D 5242; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,

2、 the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 t

3、hin-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 concer

4、ns, 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:3D 1129 Terminology Relating to WaterD 277

5、7 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD 3858 Test Method for Open-Channel Flow Measurementof Water by Velocity-Area Method2.2 ISO Standards:4ISO 1438 Flow Measurement in Open Channels UsingWeirs and Venturi FlumesPart 1: Thin-Plate Weir

6、sISO 555 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 D 1129.3.2 Definitions of Terms Specific to This Standard:3.2.1 c

7、restthe 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 over

8、falling 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 dep

9、th sensing,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.

10、9 stilling 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 ro

11、ot of the 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

12、 over the 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.3.2.13 tailwaterthe water level immediately downstreamof the weir

13、.1This test method is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.07 on Sediments, Geomor-phology, and Open-Channel Flow.Current edition approved June 15, 2007. Published July 2007. Originallyapproved in 1992. Last previous edition approv

14、ed in 2001 as D 5242 92 (2001).2The boldface numbers 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

15、 to the standards Document Summary page onthe ASTM website.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States

16、.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 experimentally or analytica

17、lly 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 section a widerange

18、 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 solids andin lo

19、cations 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 flow andbecome

20、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 instrumentthat co

21、ntinuously 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 (usually)rectangul

22、ar 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 base sufficient

23、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 7.2.5.4 and 7.2.6.3fo

24、r 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.7.2.2.2 The plane of

25、 the weir plate must be vertical andperpendicular to the channel walls. The overflow section mustbe laterally symmetrical and its bisector must be vertical andlocated at the lateral midpoint of the approach channel. If themetal plate containing the overfall section does not form theentire weir, it m

26、ust be mounted on the remainder of theFIG. 1 Rectangular WeirFIG. 2 Crest-Length Adjustment, DLD 5242 92 (2007)2bulkhead 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 7.2.3.) Thewe

27、ir 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 bottomof the approach channel are far enough from t

28、he 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 weirs are give

29、n 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 4Hmaxto 5Hmax, whereHmaxis the maximum head on t

30、he 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 WeirsWhen there are no side contrac

31、-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 WeirsThe conditions f

32、orfull 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 contraction cond

33、itions 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 45 as shown inFig.

34、 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 RelationsThe flowrate, Q

35、, 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 and effective cre

36、st lengthrespectively, and Ceis a discharge coefficient. The effectivehead, He, is related to the measured head, H, by:He5 H 1dHwhere dH is an experimentally determined adjustment forthe effects of viscosity and surface tension valid for water atordinary temperatures (about 4 to 30C); its value is c

37、onstant at0.003 ft (0.001 m). The effective crest length, Le, is related tothe measured length, L, by:Le5 L 1dLwhere the adjustment, dL, is a function of the crest length-to-channel width ratio, L/B. Experimentally determined valuesof dL for water at ordinary temperatures are given in Fig. 3.The dis

38、charge 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 relationsgiven in 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 principle Eq 1 co

39、uld 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 maintain proper

40、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 establish th

41、at 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.Experimental results are available for notch angles, u,of20toFIG. 3 Discharge C

42、oefficient, Ce, for Rectangular WeirsD 5242 92 (2007)3100. However, the most commonly used weirs are 90 (tanu/2 = 1), 53.13 (tan u/2 = 0.5) and 28.07 (tan u/2 = 0.25). SeeFig. 2.7.2.6.2 ContractionsThe conditions for full contraction oftriangular weirs are as follows:H/P # 0.4H/B # 0.2P $ 1.5 ft (0.

43、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. 2). T

44、his 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 u/2!Het!5/2(2)where Cetand Hetare the discharge coe

45、fficient and effectivehead respectively. Hetis given by:Het5 H 1dHtwhere dHtis 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 fun

46、ction 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 t

47、hese 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 maintain

48、 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 channel

49、 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, the presence o