Hidrológiai Közlöny 1959 (39. évfolyam)

1. szám - Kozák Miklós: A Rakaca-völgyi tározó árapasztó szifonjának modellkísérlete

30 Hidrológiai Közlöny 1959. 1. sz. Kozák M.: A Rakaca-völgyi tározó árapasztó modellkísérlete CKHX npiiHiíimoB — PABHOMEPHOE YBEJIHMEHHE, HUH YMEHBUIEHNE pacxoaa B HHWHCM 6beij)e. Il03T0My iipn HCcjieflyeMOM cH(J)OHe cflejiajiocb cjie^yiomee npeflJio>KeHne : BHYTPEHHHE cii(J)OHbi, KűTopbie paHbme BKJnonaioTCH B paöoTy, Ha,no npoeKTiipoBaTb no MeHbrne BHeiiiHux. Bjiaroflapa STOMy H3MeHeHHio HJIH HH>KHero 6beij)a pacxo/; BHYTPEHHIIX CH(J)OHOB B 10 M

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3/ceK. BBH^Y reojiorHHecKoro CTpoeHHH pafloHa HH>KHHH 6bei|) HY>KflaeTCH B yKpenjieHHH nyTeM OSJIHUOBKH. PeKOMeHflOBajiocb npHMeHeHHe Ha flejie MaH0MeTp0B, C nOMOLUblO KOTOpbIX MO>KHO CflejiaTb OieHb UCHHbie H3MepeHiiH nocjie nocTpoeHHH coopyweHHfl. IlyTeM conocTaBJieHIlH 3THX BeJIHMHH C BejIHMHHaMH, HaÖJHOfleHHblMH Ha MOAeJlH MOJKHO CfleJiaTb BblBOflbl OTHOCHTeJlbHO BeJIHMHHbi h xapaKTepa a^eiora MacwTa6a M0fleJiHp0BaHna. 3TH flaHHbie MoryT CTaTb IÍCHHHMH aaHHbiMii H AJM nanbHeiíijjero pa3BHTHH HayKH 11 nnn flajibHeiíujHx npoeKTHpOBaHHH. Model Tests on the Syphon Spillway for the Rakaca I)am By M. Kozák, Candidate of Technioal Sciences Investigations on the model to scale 1 : 12 of an automatical, double admission syphon spillway combined with control gates are described. The erest of the syphon shown in Fig. 1 is at elevation 154,30 m a. d., whereas the highest flood level is at 154,60 m a. d. In the verticai sense the d = 5 cm diameter pipeline, which was intended to ensure automatic priming and operation of the syphons, has been designed to start the two inner syphons and the two exteriőr syphons upon reaching reservoir levels at elevations 154,40 m a. d. and 154,50 m a. d., respectively (Fig- 1). The problem consisted of investigating the following main hydraulic questions by means of scale models of the syphons: 1. Are the venting pipelines of circular cross section tliat were provided, suitable to ensure automatic operation and separate starting of syphons whenever the water surface reaches elevations 154,40 m a. d., and 154,50 m a. d., respectively ? 2. Are the four syphons capable of coping with a flood of 40 cu. m/sec without causing the water surface to rise above elevation 154,(>0 m a. d. ? Is the generál design of the syphons satisfactory ? 3. To what extent are the syphons capable of ensuring a uniformly increasing discharge in the watercourse downstream ? It should be noted, that in order to provide for the visual inspection of hydraulic condition the model of the structure has been bisected along its axis of symmetry (Hl. 4) and one-half has only been constructed. Main results of these experiments can be summarized as follows : 1. In order to provide protection against wave action, the outer port of the venting pipeline serving the inner pair of syphons has been located very deep, so ethat air was shut off before the development of a nappe over the syphon erest, that could have primed the shaft. A space fiiled with air under pressure p> p

0 developed within the syphon, which depressed the nappe with the result that the latter could not increase in spite of the gradually rising reservoir level, i. e., head (111. 8). Consequently the syphon failed to start. In order to ensure starting at the predetermined reservoir level, pressureequalizing pipes of 3 cm diameter have been installed in the shafts, which proved an adequate solution of the problem since the syphons started to function whenever the specified reservoir level was reached (Ills. 1—3). The cross-sectional area of the circular venting pipes installed proved alsó inadequate, since the quantity of air delivered througli them was carried away by the flow in the syphon without interrupting the operation of the latter. The circular venting pipes having failed in this respect, they were replaced by a single 8 cm high by 90 cm wide rectangular air duct, which was found capable of ensuring automatic operation. It could be deducted that both dimensions and location of air ducts are a problem deserving careful attention during designing. 2. Several modifications were found necessary in the generál arrangement of the syphons. In order to reduce the danger of cavitation, the radius of curvature of the syphon erest has been increased (Fig. 2). A depression amounting to from 1.05 to 1.1 m water column was namely observed at apex of the syphon. The 4,8 m high fixed weir designed to reduce flow velocities in the tailwater has been removed, since the high tailwater level created thereby in the lower elbow of the syphon interfered with its priming, respectively with starting to discharge. Owing to the above modifications the discharging capacity of the syphons at maximum reservoir level was in excess of 40 cu. m/sec. Therefore, in order to reduce this capacity and in accordance with suggestions of the designers, the throttling effect of the syphons has been increased until the discharging capacity diminished to 40 cu. m/sec. 3. Syphons without discharge regulators are, owing to the hydraulic principles underlying tlieir operation, incapable of ensuring a uniform increase, respectively decrease in discharge. It has been suggested, therefore, to reduce the central pair of syphons relatíve to the external ones, the former starting operation earlier. A discharge through the central syphons, modified to 10 cu. m/sec as against the originál 20 su. m/sec, is more favourable as far as the protection of the tailwater cliannel is concerned. In view of the geology of the site a robust lining is deemed necessary for the tailwater channel. The installation of pressure gages in the prototype has been suggested. These would provide valuable information as to the behaviour of the syphons, and the comparison of field data with model observations would be indicative of the character and the order of magnitúdó of the scale effect. Similar information would be of both theoretical and practical interest. \