Açık kanalda askıda bitki etkisindeki akımın yatay hız bileşeninin derinlik boyunca değişiminin incelenmesi

Abstract

Ekosistem için çok önemli olan bitki tarlalarının kıyı ve akarsu hidroliği üzerindeki etkilerini incelemek son yıllarda giderek önem kazanmıştır.  Su bitki örtüsü genellikle tam batmış, kısmi batmış ve yüzen bitki örtüsü olarak sınıflandırılabilmektedir.  Yüzen bitki örtüsünün en büyük farkı bitkinin altındaki taban sınır tabakasının etkisidir.  Yüzen veya askıda bitki örtüsü akışa engel teşkil edecek ve akım hızında yavaşlamaya neden olacaktır.  Bu yavaşlama ile beraber düşey hız dağılımı klasik logaritmik dağılımdan sapacaktır.  Bitki sebebiyle üst tabakadaki hız azalmasının aksine, bitki ile taban arasında kalan boşlukta hız artışı oluşacaktır.  Bu çalışmada, 181 adet 1.0cm çaplı silindirik çubuklar, 30cm çaplı ahşap bir kafaya sabitlenmiş ve su seviyesinden itibaren 15cm su içine girecek şekilde kanal üst tarafına monte edilmiştir. Membada, bitkiden önce 4 nokta ve mansapta bitkiden sonra 7 nokta olmak üzere 11 farklı noktada ve 8 farklı derinlikte hız ölçümleri ADV (Akustik Dopler Hız Ölçer) kullanılarak yapılmıştır. Deney sonuçları, askıda bitkinin akıma engel teşkil ederek, akımın hızını etkilediğini göstermiştir.

Keywords

• Askıda bitki,düşey hız dağılımı,açık kanal akımı

Investigation of the horizontal velocity component change along the depth caused by the suspended vegetation in the open channel

Abstract

It has become increasingly important in recent years to study the effects of vegetation fields on the fluvial areas which are very important for the ecosystem.  The water plant fields can be classified as submerged, emergent and suspended vegetation.  The major difference of the suspended vegetation is the effect of the bottom boundary layer under the plant.  Suspended vegetation is obstacle and will cause a decrease in speed of the flow and the vertical velocity distribution will deviate from the classical logarithmic distribution.  Contrary the decrease in speed in the upper layer due to the plant, the speed increase will ocur in the gap beneath the plant.  In this research, 181 rigid cylinders with a diameter of 1.0cm were fixed to a 30cm diameter wooden head and mounted on the upper side of the channel.  The plant was allowed to enter into 15cm of water and there is a 15cm gap beneath the plant, between the channel bed and the plant end.  An ADV (Acoustic Doppler Velocitymeter) was used to collect data from 11 different points (4 points before the plant and 7 points after the plant) and 8 different depths.  Experimental results have shown that the suspended vegetation is a barrier to flow and affects the the velocity of the flow.

Keywords

• Suspended vegetation,vertical velocity distribution,open channel flow

References

1. David R. Plew, Robert H. Spiegel, Craig L. Stevens, Roger I. Nokes, Mark J. Davidson, Stratified flow interactions with a suspended canopy, Environmental Fluid Mechanics, 6, 519-539, (2006).
2. Wenxin Huai, Yang Hu, Yuhong Zeng, Jie Han, Velocity distribution for open channel flows with suspended vegetation, Advances in Water Resources, 49, 56-61, (2012).
3. David R. Plew, Depth-Averaged drag coefficient for modelling flow through suspended canopies, Journal of Hydraulic engineering, 137(2), 234-247, (2011).
4. Amir Heshmatifar and Mirmosadegh Jamali, A study of effect of floating vegetation on the formation of exchange flow, 10th International Congress on Civil Engineering, University of Tabriz, Iran, 5-7 May, (2015)
5. Xueyan Zhang, Heidi M. Nepf, Exchange flow between open water and floating vegetation, Environ Fluid Mechanics, 11, 531-546, (2011)
6. David R. Plew, Craig L.Stevens, Robert H. Spiegel, Neil D. Hartstein, Hydrodynamic implications of large offshore mussel farms, IEEE Journal of Oceanic Engineering, 30(1), 95-108, (2005)
7. Järvelä, J., Effect of submerged flexible vegetation on flow structure and resistance. Journal of Hydrology, 307, 233-241, (2005)
8. Yüksel Ozan, A., Bitki parçasının açık kanal en kesiti boyunca neden olduğu akım yapısı, Pamukkale Üniversitesi Mühendislik Bilimleri Dergisi, PAJES-71300, 23(6), 726-731, (2017)

9. Huai, W.X., Zeng, Y.H., Xu, Z.G. and Yang, Z.H., Three-layer model for vertical velocity distribution in open channel flow with submerged rigid vegetation. Advances in Water Resources, 32, 487-492, (2009).
10. Nepf, H.M. and Vivoni, E.R., Flow Structure in depth limited, vegetated flow, Journal of Geophysical Research, 105(C12), 28547-28557, (2000).
11. Nezu, I. and Okamoto, T., Large eddy simulation of 3-D flow structure and mass transport in open channel flows with submerged vegetations, Journal of hydro-Environment Research, 4, 185-197, (2010).
12. Raupach M.R., Canopy Transport Processes, In: Steffen W.L., Denmead O.T. (eds) Flow and Transport in the Natural Environment:Advances and Applications, Springer, Berlin, Heidelberg, 95-127(1988),
13. Fischer-Antze, T., Stoesser, T., Bates, P., and Olsen, N.R.B. 3D numerical modelling of open-channel flow with submerged vegetation, Journal of Hydraulic Research, 39(3), 303–310, (2001).
14. Li, Y., Wang, Y., Anim, D.O., Tang, C., Du, W., Ni, L., Yu, Z., and Acharya, K., Flow characteristics in different densities of submerged flexible vegetation from an open-channel flume study of artificial plants, Geomorphology, 204, 314–324, (2014).
15. Sarker, A., Flow measurement around scoured bridge piers using Acoustic-Doppler Velocimeter-ADV, Flow measurement and instrumentations, 9, 217-227, (1998).
16. WinADV32(v.2.027) Manual 2009
17. Newel, C.R., Richardson, J., The effect of ambient aquaculture structure hydrodynamics on the food supply and demand, Journal of Shellfish Research, 33(1), 257-272, (2014)