Table of Contents. Contents and Preliminary Pages. Methods of flow regulation. Design considerations. Applications of side weirs. Flow characteristics of weirs. Hydraulic design method. Application to practical problems. Appendix I. General theory of side weirs. Appendix 2. Evaluation of alternative solution methods. Appendix 3. Development of design method.
Hydraulic design of side weirs
No articles to recommend. Each labyrinth weir models with a sharp crested shape was tested with and without nappe breakers in the experiments Examples shown in Figure 3. Level measurements were taken at a distance from the weir equal to five times the nappe height. For flow rate measurements, Nortek brand acoustic three-axis velocimeter was used.
In the experiments, the weir heights were taken as mm, mm and mm and apex width A was taken as 80 mm. Sharp-crested shapes is provided for all models. All experiments were performed according to free flow conditions. The flow over labyrinth weir is three dimensional and does not readily fit into mathematical description and hence the discharge function is found through experimental studies and analysis.
The crest coefficient depends on the total head, weir height, thickness, crest shape, apex configuration and angle of side wall. To simplify the analysis, the effect of viscosity and surface tension could be neglected by selecting model and velocity of sufficient magnitude. The discharge over labyrinth weir can be expressed as:.
Head over labyrinth weir was measured for different value of discharges in the range of In this range, the head over the labyrinth weir varied from 10 to 90 mm. The model of linear weir is also tested in the same flume for the purpose of comparison.
Design of Side Weirs | Liquids | Chemical Engineering
In the experiments, the characteristics of different types of the weirs which are tested in the experiments are given in Table 1. The objective of this research is to further the understanding related to the mechanisms that cause nappe vibration, document the occurrence conditions, and investigate mitigation techniques for trapezoidal and circular labyrinth weirs. Figure 1. Experimental arrangement. Figure 2. Schematic view of the trapezoidal and circular labyrinth weirs located on straight channel. Figure 3. Experimental set-up for: a Trapezoidal labyrinth weir b Trapezoidal labyrinth weir with nappe breakers c Circular labyrinth weir d Circular labyrinth weir with nappe breakers.
Figure 4. Definition sketch for flow over a sharp crested weir. Table 1.
Physical model geometrics for weirs tested in the present study. In addition, experiments were repeated by placing nappe breakers on all models of the labyrinth weirs. A total of 24 different configurations were examined in these experiments. Discharge coefficient for labyrinth weirs was computed using equation Equation 4. Discharge coefficients of labyrinth side weirs have much higher values than the conventional weirs.
The effect of crest shape on the discharge coefficient is very significant for the same channel width and crest length. In this study, the nappe breakers installed on the crest spaced at a regular interval is a remedy used on prototype spillways to eliminate nappe oscillation. The nappe breakers create a break in the continuous lateral nappe profile, venting the confined air pocket if one exists behind the nappe to atmospheric pressure.
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Anderson, A. The results of this experimental study showed that adding more nappe breakers and shortening the spacing is most effective at disrupting the vibration. This, of course, is a general statement on what was observed on this model, and does not provide specific nappe breakers spacing design parameters for any given weir spillway. The variation of C d for trapezoidal labyrinth weirs with nappe breakers is plotted in Figure 6 and the variation of C d for circular labyrinth weirs with and without nappe breakers is plotted together in Figure 7.
It is noted that discharge coefficient for labyrinth weirs is computed using equation Equation 4. It is apparent from the results in Figure 5 and Figure 6 that discharge capacity of the labyrinth weirs is much higher than the conventional weirs. The primary reason for this is that the crest length of the labyrinth weir is much longer than that of the conventional weir. Nappe breaker constitutes an impediment in the direction of flow and it decreases the length of the overflow. Therefore, discharge capacity of the labyrinth weir without breaker is more than that of the labyrinth weir with nappe breaker.
Figure 6. Figure 7. The discharge capacity of trapezoidal labyrinth weirs according to the circular labyrinth weirs can be seen to be higher in Figure 8. The important effect of nappe breakers on discharge coefficient can be seen in the range from 0. To represent the data of the equation form, correlation analysis is carried out for the observed data for each model, separately.
Thus, discharge coefficient C d of sharp-crested labyrinth weir with and without nappe breaker is expressed as:. The discharge coefficient values of labyrinth weir compared well with those of Woronora Dam, Boardman Dam, and Avon Dam. Moreover, the results of the present study compared well with those of Tullis et al.
Although the data values are different, due to the variation in nappe shape and side wall angle for each study, the trends are similar to the findings of Tullis et al. Labyrinth weirs can pass large flows at comparatively low heads. The crest shape is one of the most important factors which affect the discharge capacity for labyrinth weirs. According to this experimental study, it has found that the trapezoidal labyrinth weirs are hydraulically more efficient than the circular labyrinth weirs and linear weirs from the perspective of ease of construction and the discharge capacity.
Variation of the nappe pressure between sub-atmospheric pressure and atmospheric pressure causes vibrations, oscillations and noise. Although the negative pressures under water nappe partially increase the discharge ca-. Figure 8. Figure 9.
Table 2. Coefficient of discharge per unit length of trapezoidal labyrinth weir. Figure Alleviation of these effects and to minimize the dynamic effects on structures can be possible with the nappe breakers which are placed on the labyrinth weirs. While it has been targeted to minimize these dynamic effects. Table 3. Coefficient of discharge per unit length of trapezoidal labyrinth weir with nappe breakers. Table 4. Coefficient of discharge per unit length of circular labyrinth weirs with and without nappe breakers.
Of course, given unlimited width, greater efficiencies discharge per head will be obtained for a linear weir.
However, the trapezoidal provides much greater weir length in confined space with only limited reductions in efficiency reduction in C d. The circular weir is the least efficient of those investigated. The nappe breakers located on the weir crest have proven to be an effective countermeasure by several researchers, but specific spacing of nappe breakers for a weir of a given height and width has not been determined and would be a valuable focus of future research, along with further investigation of the aspect ratio of flow depth to nappe width conducive to nappe vibration.
A better understanding of the causes and preventative measures of nappe vibration will aid engineers in the design of dam spillways structures. The authors gratefully acknowledge the assistance of Mr. Javad Roostaei in the preparation of Figures and Tables for this manuscript. Omer Bilhan,M. Emin Emiroglu,Carol J.
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