EXPERIMENTAL STUDY OF TURBULENT FLOW STRUCTURES IN TWO GROYNES FIELD USING PIV METHOD

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SAFARZADEH Z.; SAFARZADEH A.

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Journal: Modares Civil Engineering journal Year:2016 | Volume:16 | Issue:1 Page(s): 69-80

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Title

EXPERIMENTAL STUDY OF TURBULENT FLOW STRUCTURES IN TWO GROYNES FIELD USING PIV METHOD

Author(s)

SAFARZADEH Z. | SAFARZADEH A. | Issue Writer Certificate

Keywords

TURBULENT FLOWQ2

MIXING LAYERQ2

SPIVQ2

BACK FLOWQ2

VORTICITYQ2

Abstract

In this paper, the flow field between two straight groynes in shallow wide open channel has been measured using Particle Image Velocimetry method. Groynes with 25cm length, 5cm width and 7cm height with two aspect ratios (l) of 1 and 2 have been located in the fully developed zone of a 18m length flume and velocity measurements carried out in order to study the circulating flow, structure of the MIXING LAYER and downstream separation zone. Surface Particle Image Velocimetry was conducted using two Procilica GE1910 CCD cameras with 37 Hz measuring frequency. Images resolution was 90*1660 pixeles. Image processing was performed using GPIV software and Westerweel, 2005 and Brevis, 2009 methods were used for filtering of the measured velocity fields. Matlab programs were developed for the post processing of the measured data. Results are presented in forms of time averaged values, turbulence intensities and the Reynolds stresses at the various zones of the groyne field. Results showed that due to the flow shallowness, most of the turbulent structures are two dimensional. Development of a BACK FLOW from downstream zone to the groyne field enhances the complexity of the MIXING LAYER and mas exchange phenomenon compared to the groyne series configuration. In the l=1 case, a fully developed gyre forms inside of the groyne field. The circulation zone is connected to the MIXING LAYER at the head of the upstream groyne. By increasing the distance between the groynes, i.e., for the l=2 case, another circulation zone forms inside of the MIXING LAYER. Consequently the circulation zone inside of the groyne field is depressed in the transverse direction. In the both cases a single gyre forms inside of the groyne field. While, the previous works showed that in the groyne series case, by increasing the aspect ratio, number of the gyres between groynes increases. Furthermore, unlike to the two groynes case, gryres rotate in the clockwise direction.In two groyne case, the rotational energy is fed from the VORTICITY of the BACK FLOW to the circulation zone in the groyne field, while in the groyne series case, the momentum transfer between the free flow and the dead zone in the groyne field is responsible for the formation of multiple gyres inside of the groyne field. Two groynes field has complex dynamic flow features and it is not a suitable choice for modification of the river alignment or the bank stabilizing projects. On the other hand, they move the high velocity zone to the channel center and they could be used as protection measures for the river structures like bridge abutments.The MIXING LAYER of two groynes case is fully dynamic and it can deeply penetrate into the groyne field. While, in the groyne series case, exchange processes between dead zones and main stream are governed by large coherent two-dimensional structures which are generated at the head of the upstream groyne. Consequently, in terms of the environmental issues, the retention time of the trapped pollutants in a two groynes field will be shorter than the groyne series case.

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APA: Copy

SAFARZADEH, Z., & SAFARZADEH, A.. (2016). EXPERIMENTAL STUDY OF TURBULENT FLOW STRUCTURES IN TWO GROYNES FIELD USING PIV METHOD. MODARES CIVIL ENGINEERING JOURNAL, 16(1), 69-80. SID. https://sid.ir/paper/256735/en

Vancouver: Copy

SAFARZADEH Z., SAFARZADEH A.. EXPERIMENTAL STUDY OF TURBULENT FLOW STRUCTURES IN TWO GROYNES FIELD USING PIV METHOD. MODARES CIVIL ENGINEERING JOURNAL[Internet]. 2016;16(1):69-80. Available from: https://sid.ir/paper/256735/en

IEEE: Copy

Z. SAFARZADEH, and A. SAFARZADEH, “EXPERIMENTAL STUDY OF TURBULENT FLOW STRUCTURES IN TWO GROYNES FIELD USING PIV METHOD,” MODARES CIVIL ENGINEERING JOURNAL, vol. 16, no. 1, pp. 69–80, 2016, [Online]. Available: https://sid.ir/paper/256735/en

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