2012 沐若台阶式溢洪道掺气减蚀设施研究
Procedia Engineering 28 (2012) 803 – 807
1877-7058 ? 2012 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Society for Resources, Environment and Engineering
doi:10.1016/j.proeng.2012.01.813
2012 International Conference on Modern Hydraulic Engineering
Aerator of stepped chute in Murum Hydropower Station
WANG Si-ying a , HOU Dong-mei, WANG Cai-huan, a*
Changjiang River Scientific Research Institute, Wuhan, Hubei, 430015, China
Abstract
This paper considers the effect of an aerator type to counter cavitation damage on the stepped chute in Murum Hydraulic Power Station. The shape of the aerator was optimized and the aeration effect was observed by hydraulic modeling. The experimental results revealed that, compared to standard stepped spillway flow, considerable differences were detected in the closely downstream of the aerator. Steady cavities were formed and flow before the point of incipient self-aeration was pre-aerated, and the air concentration of bottom flow on the stepped chute was obviously increased, which means the cavitation damage was successfully avoided.
? 2011 Published by Elsevier Ltd.
Keywords: aerator; stepped chute; Murum Hydropower Station; air concentration; cavitation damage
1. Introduction
The Roller Compacted Concrete (RCC) technic, which is convenience to construct steps, was put forwad when the Willow Creek Dam was build in 1980s. The stepped chute/dam then has been fast developed since the first stepped dam (Up Still Dam) was build in America twenty years ago. Considering the advantage in constructing time ，project investment, and energy dissipation, stepped chutes have been wildly applied in China, such as Dongxiguan, Danjiangkou, Shuidong, Baise, and Dachaoshan hydropower stations[1]. About these stepped discharging constructions, much work has been done on the flow patterns[2-5], energy dissipation ratio[6], energy dissipator[7], impact effection of converging walls[8,9] and so on 。Since the underwater steps reduce the smoothness of the dam surface, negative pressure may measured and cavation erosion might occur. For example, Danjiangkou reservior used constructing reserved steps to discharging floods with flux over 100m 3/(s·m), and then in the inspection
* Corresponding author. Tel.: 027-********. E-mail address : thing@https://www.wendangku.net/doc/7515640435.html,.
? 2012 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Society for Resources, Environment and Engineering
804WANG Si-ying et al. / Procedia Engineering 28 (2012) 803 – 807
after flood protection, cavatation erosion was detected somewhere on the stepped dam surface[10]. It is a challenging probem to avoid cavatation damage on stepped chute with water flow in large unit width discharge. Both internal and overseas researchers have paid their attention to the aerator of stepped discharge constructions. Pian & Zhang[11] studied on the length of the air cavity behind and jet aeration capacity of flow over the aerator. Zhang et al[12] and Ren Yu[13] studied the time averaged pressure characteristic of stepped spillway. Pfister et al[14] considered the effect of two aerator types located at the first vertical step face to add air to the chute bottom. Zamora et al[15] optimized the step aerator by hydraulic modeling to design the air supply and to indicate the aerator blockage characteristics. In China, some constructed and constructing hydraulic power stations such as Shuidong, Dachaoshan, and Suofengying applied stepped dam surface associate with flaring gate pier and stilling basin to dissipate energe[16,17].
This work studied the aeration effection of the stepped spillway of Murum Hydraulic Power Station, and optimized the prepositive aerator by hydraulic modeling. The flow characteristic, water surface, pressure, and aeration were compared and the air entrainment to alleviate cavitations effection was validated and can be referred by similar projects.
2. Experimental setup
The RCC gravity dam of Murum Hydropower Station is 146m high with 7m width on the dam top. This dam adopts WES weir crest without a gate, using four surface holes to discharge flood. The width of each surface hole is 13.5m and the maximal discharge per unit width is 39.21m3/s. This dam uses stepped dam surface combined with deflecting flow to dissipate energy. There are 120 steps on the dam surface, each of which the width is 0.8m and the height is 1.0m. We chose the two middle surface holes as research object, studied flow on the spillway using a 1:40 scaled section model test.
Fig. 1. Vertical section drawing of Spillway of Murum Hydropower Station
Basing on the original design scheme, we designed and optimized an aerator composed of flaring gate piers and a flip bucket located at the first vertical step face to protect the dam crest from cavitation damadge. The shape of the aerator is as follow:
805
WANG Si-ying et al. / Procedia Engineering 28 (2012) 803 – 807
Fig. 2. Shape of the aerator
In different hydraulic conditions, the flow patterns on the dam surface were observed, and the water surface profile, pressure characteristic, and aeration effect were also investigated. The experimental results were described in the next section.
3. Experimental setup
3.1. Flow characteristics
Table 1 exhibits the vertical water depth distribution on the stepped dam of the original design scheme
and of the optimized scheme with aerator.
Table 1. Vertical water depth distribution on the dam surface (m)
Point Point Position
Q=2160m3/s Q=1570m3/s Q=480m3/s Q=2160m3/s Q=1570m3/s Q=480m3/s
S1 Gate pier 2.5 2.0 0.7 2.9 2.3 1.0 S2 1st step 2.2 1.7 0.7 3.0 2.3 1.1 S3 10th step 1.6 1.2 0.7 2.5 2.0 0.9 S4 20th step 1.7 1.2 0.7 2.2 1.6 0.8 S5 30th step 1.7 1.3 0.7 1.8 1.4 0.7
Fig. 3. Cavums formed behind the aerator（Q=2160m3/s）
806WANG Si-ying et al. / Procedia Engineering 28 (2012) 803 – 807 Though the discharging capacity of each surface hole is not affected by the aerator, the vertical water depth of the first 30 steps on the dam surface is drived up by the flip bucket and the flaring gate piers, especially under a larger flood. For the downsteam behind the 30th step, the water surface profile basically keeps the same. From figure 3, we can see that the free jet from the flip bucket joints well with the downsteam flow and no bad flow pattern is observed. Steady cavums are formed behind the flaring gate piers and at the bottom. The bottom cavum extends to the 5~6th step and the area of the medial cavum is about 1.3m×6.5m (width×length), half of which the the lateral cavum is. All the cavums are connected as
a whole and obvious aerated flow is observed in the downstream of the aerator.
3.2. Aeration effect
The pressure distribution on the dam surface doesn’t change much in the optimized and original schemes. Because of the flip bucket, the maximal average pressure increased from 2.62×9.81kPa in the design scheme to 3.82×9.81kPa in the optimized scheme. While the minimal value doesn’t alter much, retaining with an absolute value smaller than 0.38×9.81kPa. The experimental results reveal that, the fluctuating pressures measured on the upstream dam surface before the 40th step are minished, which means a larger air concentration. The air concentration of the bottom flow on the dam is list in Table 3. Table 3. Air concentration of the bottom flow（%）
Test Point Point Position
Q（m3/s）
Original design scheme Optimized scheme with aerator
2160 1570 480 2160 1570 480 th
C2 Central line of the chute 20th step 1.8 2.5 12.6 5.0 6.5 19.4
C3 Central line of the chute
30th step 2.2 3.0 21.1 5.3 7.0 24.8
C4 Axis of the middle pier 2.3 3.2 22.0 7.1 9.9 22.3
C5 Central line of the chute
40th step 5.2 5.6 23.6 6.5 12.5 28.3
C6 Axis of the middle pier 3.5 4.6 23.4 6.8 12.0 23.1
C7 Central line of the chute
50th step 13.0 19.6 29.9 14.9 20.3 33.8
C8 Axis of the middle pier 5.5 11.8 30.2 7.6 10.4 23.4
C9 Central line of the chute
60th step 15.4 21.4 32.8 18.3 22.9 35.3
C10 Axis of the middle pier 7.8 15.4 33.1 12.6 18.7 35.0 C11 Central line of the chute 70th step 18.4 24.0 34.0 21.7 25.1 34.7
Comparing to the values in the original design scheme, the air concentration of the bottom flow on the dam surface is obviously increased in the optimized scheme with aerator. The air concentration values all exceeds 5% in the range behind the flip bucket, and exceed 10% for the downsteam self-aerated flow. Those results were measured with the flow velocity smaller than 6m/s in model experiment, for which the corresponding prototype air concentration would be much weakened for the scale effect. Referring to the Dachaoshan Hydropower Station, the air concentration of the prototype flow is about 2-3 times that measured in the model test. So we deduced that the air concentration of the whole flow on the prototype stepped dam surface of Murum Hydropower Station can exceed 10%, and the cavitation damage could be avoid.
807
WANG Si-ying et al. / Procedia Engineering 28 (2012) 803 – 807
4. Conclusion
An preposition aerator type composed of a flip bucket and flaring gate piers was designed to counter cavitation damage on the stepped spillway in Murum Hydraulic Power Station in Malaysia. The conclusions of the hydraulic model study in this paper are as follows. First, the discharging capacity of
each surface hole and the flow pattern in the far downstream of the aerator are not obviously affected by
the aerator. Secondly, steady bottom and lateral cavums are formed behind the aerator and obvious pre-aerated flow is observed in the downstream. Finally, the air concentration of the flow on the stepped dam surface is obviously increased and the cavitation damage could be avoided.
References
[1]. Wu xiansheng. Review on the application of stepped chutes in China. Sichuan Water Power, Vol.24, No.1, pp:22-26, 2005.
(In Chinese)
[2]. Chanson Hubert. Hydraulic design of stepped spillways and downstream energy dissipators. Dam Engineering, Vol.11, No.4,
pp:205-242, 2001.
[3]. Gonzales C. A., Chanson H. Hydraulic design of stepped spillways and downstream energy dissipators for embankment
dams. Dam Engineering, Vol.17, No.4, pp:223-244, 2007.
[4]. Robert M. Boes, Willi H. Hager. Two-phase flow characteristics of stepped spillways. Journal of hydraulic engineering,
Vol.129, No.9, pp:661-670, 2003.
[5]. Chaiyuth Chinnarasri, Somchai Wongwises. Flow patterns and energy dissipation over various stepped chutes. Journal of irrigation and drainage engineering，Vol.132, No.1, pp:70-76, 2006.
[6]. Tian jianing, An tianyangyi, Li jianzhong. Energy dissipation of stepped discharge structure. Journal of hydroelectric engineering, Vol.28, No.2, pp:96-100, 2009. (In Chinese)
[7]. Dai qiuping. Development and research of energy dissipating modes of stepped spillways. Journal of Heilongjiang hydraulic engineering, Vol.35, No.2, pp:10-12, 2008. (In Chinese)
[8]. Hunt S. L., Kadavy K. C., Abt S. R., Temple D. M.. Impact of converging chute walls for RCC stepped spillways. Proceeding of world environmental and water resources congress, EWRI, ASCE, Reston, 2005.
[9]. Hunt S. L., Kadavy K. C., Abt S. R., Temple D. M. et al. Impact of converging chute walls for roller compacted concrete
stepped spillways, Journal of hydraulic engineering, Vol.134, No.7, pp:1000-1003, 2008.
[10]. Yang Min, Xi Xianhua, Ren Hongliang, et al. Hydraulic characteristic of flow on stepped dam. Discharging construction
and high speed flow. Jilin Sicence and Technology Press, Chang Chun, pp:29-33, 1998. (In Chinese)
[11]. Pian Yingchun, Zhang Zhichang. Experimental research on the length of the air cavity behind and jet aeration capacity of
flow over aerator on stepped spillways. Chinese journal of applied mechanics, Vol.22, No.4, pp:41-49, 2006. (In Chinese)
[12]. Zhang zhichang, Zeng dongyang, Zheng aman, Liu Yafei. Experimental research on pressure characteristic of flow on stepped spillway. Journal of hydrodynamics, Vol.18, No.5, pp: 652-659, 2003. (In Chinese)
[13]. Ren Yu, Wang Chengen, Liu Bin. Experimental study on the average pressure on the stepped spillway surface. Yellow
River, Vol.33, No.3, pp:123-124, 2011. (In Chinese)
[14]. Michael Pfister, Willi H. Hager, F.ASCE, Hans-Erwin Minor. Bottom aeration of stepped spillways. Journal of hydraulic engineering, Vol.132, No.8, pp:850-853, 2006.
[15]. Anina Schiess Zamora1, Michael Pfister, Willi H. Hager, F.ASCE, Hans-Erwin Minor. Hydraulic performance of step aerator. Journal of hydraulic engineering, Vol.134, No.2, pp: 127-134, 2008.
[16]. Yin jinbu, Liang zongxiang, Liu hansheng. Study on flow aeration to prevent cavitation on stepped spillway. Journal of Changjiang River Scientific Research Institute, Vol.22, No.4, pp:1-4, 2005. (In Chinese)
[17]. Wu Shourong, Zhang Jianmin, Xu Weilin, Peng Yong. Experimental investigation on hydraulic characteristics of the flow
in the pre-aerator stepped spillways. Journal of Sichuan university(Engineeering Science Edition), Vol.40, No.3, pp:37-42, 2008. (In Chinese)