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Khusankhodjaev Ulmas Imamovich, Candidate of Technical Sciences
Tashkent Institute of Architecture and Construction
Baymatov Sh. Kh., Senior Lecturer,
Tashkent Institute of Architecture and Construction
Zhuraev K. T., Junior Lecturer
Tashkent Institute of Architecture and Construction E-mail: sherzod88.2017@mail.ru
TO THE QUESTION OF CAPACITY DETERMINATION OF TUNNEL SPILLWAYS
Abstract. This article presents the results of hydraulic studies to determine the capacity of a tunnel spillway at partial opening of the gates, and shows the curves of water flow as a function of the water depth of the upstream at various stages of gate opening.
Keywords: capacity, water discharge, tunnel spillway, head, upstream level, discharge coefficient, compressed depth, differential.
The main purpose of these studies is to determine the capacity of a tunnel spillway at various stages of gate opening and water levels in the upstream.
When conducting research, a tunnel spillway of hydro power plant No. 1 on the Vakhsh river has been chosen as an object of the study; it includes the power supply path. The water power supply structure also includes a water intake of 40 m height of tower type with two openings of total width of10 m.
Since the solution of the problem of capacity determining by the calculation method with sufficient accuracy is not possible because of the inconsistency of the design scheme, the studies have been conducted on the hydraulic model of the tunnel spillway built on a scale of 1:60 of actual size.
The model shows:
1. A section of the upstream with dimensions of 120 x x120 m with bottom relief.
2. Entry crown of the right thread and transition section from the entry crown to the supply tunnel.
3. The headrace energy path with connection to the actual spillway tunnel.
4. The downstream channel section of 200 m length.
The tunnel model is made of organic glass.
The flow through the tunnel passes at an appropriate water levels in the downstream along the flow curve of the water gauge station. Water levels in the upstream and downstream have been recorded on the model with water-measuring needles, and water flow has been measured at the end of the model with a trapezoid spillway 0.5 m deep across the bottom.
Water is supplied to the model through a pipeline from a pumping station connected to a reservoir located in a closed circuit of water supply and water discharge paths.
The research includes the following issues:
- determination of flow rates and water levels in the upstream at randomly selected stages of gate openings, a = 0.98; 2.0; 4.0; 6.0; 8.0m
- determination of the dependence of discharge coefficients "y" of the spillway on gate opening and the water depth in the upstream.
Figure 1. Hydraulic design
It should be noted that the capacity definition of a tunnel spillway is usually determined by design scheme 1 shown in (Fig. 1). However, the design scheme adopted for our design of the spillway (see figure 2) differs from the design (scheme 1).
The difference lies in the fact that directly behind the gate in the bottom of the spillway, a ledge of 0.5 m high is arranged (see Fig. 2).
The following assumptions have been made.
1. The ledge in the bottom is moved down to a distance l > a
2. The compressed depth is moved to the bottom behind the ledge without taking into account the pressure losses in this area (as immeasurably small).
3. The additional head formed when transferring hcomp to the bottom behind the ledge is not taken into account, since its magnitude is a fraction of a percent of the total head, and could be neglected.
Water discharge in scheme 2 is determined by the formula.
Q = yua bj 2 g-Az (^
where M - is the coefficient of discharge.
b - is the span width, m a - is the height of gate opening, m A - is the design head, m
AZ = H + Pet - \omp (2)
where: H is the water depth in the upstream relative to the bottom of the threshold, m
Pset - is the height of the ledge, m h - is the water depth in the compressed section, m
comp il-'
hcomp =£'a (3)
£ - is the vertical compression ratio of the jet e =f(a/h) [2].
Figure 2. Hydraulic design
Figure 3. Dependences of the discharge coefficient "p" on the head "H": a) at gate opening a = 0.98 m; b) at gate opening a = 2.0.m; c) at gate opening a = 4.0.m; d) at gate opening a = 6.0.m; e) at gate opening a = 7.0.m; f) at gate opening a = 8.0.m
The capacity of the spillway was determined experimentally on the model. Experiments have been carried out at gate openings a = 0.98; 2.0; 4.0 6.0; 8.0 m, in symmetrical operation of the gates and separate operations of each opening. At the same time, the water depth in the upstream and the corresponding flow rates have been measured.
Based on the results of experiments, the discharge coefficient of the spillway "y" in the section upstream-compressed depth was determined.
The definition of design head was made taking into account the above-mentioned ledge in the bottom of the spillway behind the gates.
According to the results of experimental studies, the dependences of the change in the discharge coefficients "y" on gate opening "a" and on water depth in the upstream "H" have been constructed. (Figure 3, a-f).
The analysis of these dependences allows us to conclude that within a single opening of the gate, the flow coefficient "y" can be considered constant, regardless of the change in water depth in the upstream.
Based on the curves of dependences y = /(H), a curve for the opening of the gates versus the flow coefficient y = /(a) has been constructed.
This dependence curve (see Fig. 4) shows that the flow coefficient ^ remains constant for the values of gate opening "a" from 0 to 4.5 m: and then increases with increasing "a" (Fig 4). H
0,9
0,85 0,8 0,75 0,7
ri
\
\
-- 0
(a)
a,M.
Figure 4. Dependence of the discharge coefficient "u" on gate opening "a" in the range of head change "H" from 8.0 to 60 m
Figure 5. Dependences of water depth in the upstream "H" of a tunnel spillway on the flow rate "Q" at various stages of gate opening
The dependence y = /(a) makes it possible to determine the value of "y" for various openings of the gates "a" and then
calculate the capacity of the spillway at different water depths in the upstream.
The results of calculation are presented in the form of the curves of water flow Qthrough the spillway versus the depth ofwater in the upstream at various stages of gate opening with intervals of 1.0 m (Fig. 5).
It has been established by experiments that when one span is operating, the value of the flow coefficient "y" versus the gate opening "a" practically does not differ from the dependences y = f (a) for symmetric operation of two openings.
So, in hydraulic calculations of tunnel spillways of this type, the scheme 2 should be used as a design scheme (Figure 2).
Thus, the water discharge through a tunnel spillway with a known opening of gates and known water depth in the up-
Consequently, according to the dependences Q=f (H; a) shown in Figure 5 it is possible to determine the flow rate of the tunnel spillway at any opening of the gates.
It should be noted that the data on water discharge calculated by the first design scheme compared with those calculated by the second design scheme (experimental data) show significant deviations - the relative error is about S = 15-20%, which is unacceptable (Table 1).
stream is determined by formula (l) or by curves (Fig. 5) for symmetrical opening of the gates.
Table 1.
^ m. а, m Q, m3/s Design scheme 2 (experiment) Q, m3/s Design scheme 1
61.2 0.98 248.31 193.3
24.4 0.98 156.25 125.18
60.4 4.0 993.45 814.7
42 4.0 812.42 678.9
12.6 4.0 397.9 378.0
42.66 6.0 1257.15 1028.0
24.54 6.0 910.27 789.1
61.8 8.0 2245.0 1847.0
24.8 8.0 1294.0 1060.0
References:
1. Rasskasov L.N et al. Hydrotechnical Structures.- M., Stroyisdat. 2014.- 486 p.
2. Kiselev P. G. Handbook on Hydraulic Calculations.- M., Energy. 1974.- 400 p.
3. Levi I. I. Simulation of Hydraulic Phenomena.- M., Gosenergoizdat. 1960.- 200 p.
4. Technical report "Experimental Laboratory Study on the Hydraulics of Tunnel Spillway".- Tashkent. 1994.- 38 p.
5. Hydrotechnical Structures: Designer's Guide. Zheleznyakov G. V., Ibad-zade Yu.A., Ivanov P. L. and others, V.P.- M., Stroyizdat, 1983.- 543 p.
