انجمن هیدرولیک ایران نشریه علمی هیدرولیک 2345-4237 19 1 2024 03 20 Investigation of flow characteristics at the confluence of two compound channels (Numerical study) بررسی خصوصیات جریان در محل تلاقی دو کانال مرکب (مطالعه عددی) 13 27 177242 10.30482/jhyd.2023.376664.1627 FA سید محمدمهدی عالمی دانشجوی کارشناسی ارشد، دانشکده مهندسی عمران، دانشگاه سمنان، سمنان، ایران. حجت کرمی دانشگاه سمنان Journal Article 2022 12 20 Introduction The junction of open channels is one of the most important points that must be carefully studied. Because the phenomenon of the intersection of channels or rivers is very common, from nature to cities. On the other hand, the flow behavior at these points is very fast, complex and different due to the connection of two or more flows with different characteristics. Many and different studies have been done on this field, with different conditions and forms of the channel section. But the main goal of this article is to investigate the flow behavior at the junction of two compound channels. But according to the literature review and past researches, it can be concluded that the most of the researches included channels with a rectangular section, while most of the natural sections are closer to the compound section. Therefore, here the intersection of channels with a compound section is investigated. Methodology Until the last three decades, the study of fluid movement and the investigation of existing phenomena in this field, were only using experimental or analytical methods, with many assumptions to simplify it. But with the advance of computers, researchers were able to investigate more complex phenomena. One of these scientific fields that has made significant progress with the increase in computing power, is computational fluid dynamics or CFD, and one of its branches is hydraulic. Microscopic investigation of water behavior in natural streams is complex. Solving the existing theoretical models, in their complete form and with all the improvements, does not have the ability to correctly simulate its changes. But with the advance of computers, the science of CFD was able to successfully simulate and predict the behavior of water by using turbulence models. which There are different turbulence models with different applications that are used according to the type of problems. For calibration the model, the simulation’s results is compared with the experimental data. If the amount of error was small, it is concluded that the modeling has sufficient accuracy. So it is possible to continue the research and simulating other samples that have not been done in the laboratory, using Flow-3D software, and the effect of different parameters is investigating. Results and Discussion The profile of the water level in all cases of the intersection of two channels is such that the height of the water reaches a maximum in the middle of the intersection and then decreases to a minimum at a distance of about one meter from the intersection. After this point, the height of the water increases again to reach the equilibrium state. . However, among the effective parameters on the depth of water inside the channel, the effect of ratio of width of the channels, ratio of the flows and trapezoidal channel were investigated, with the assumption of constant angle of intersection of two channels (90 degrees). Reducing the slope of the channels wall up to 10.5%, reducing the ratio of the main flow to the side channel up to 4.2% and reducing the ratio of the width of the main channel to the width of the side channel up to 33%, leads to a decrease in the minimum water depth compared to the base model (with a rectangular cross-section and a flow ratio of 0.25). Also with increasing the ratio of flow to maximum, the minimum depth increased by 7.5%. The velocity and the turbulence energy were investigated for four specific simulations in order to get a better understanding of the intersection of two compound channels. Conclusion The main changes and characteristics of the intersection of two channels, are related to the characteristics of the sub-channel and are the result of the effect that the momentum of the sub-flow has on the main flow. U-velocity in the trapezoidal channel, decreased by 13.76% compared to the rectangular channel, and also the u-velocity in the minimum flow ratio was 1.33 times higher than the model with the maximum flow ratio. This indicates the importante effect of the sub-channel. تلاقی رودخانه‌ها یا کانال‌ها، پدیده‌ای رایج است. اما علی‌رغم شباهت بیشتر مقاطع رودخانه‌ها به مقطع مرکب و نیز تفاوت‌های آن با مقاطع ساده، به نظر می‌رسد مطالعات جامعی در خصوص تلاقی دو کانال مرکب صورت نگرفته است. برای اعتبارسنجی مدل، نتایج شبیه‌سازی با داده‌های آزمایشگاهی مقایسه گردید. مقادیر سه معیار MAE، RMSE و R2 برای بهینه‌ترین شبیه‌سازی با مدل آشفتگی K-w، به ترتیب برابر 0175/0، 0189/0 و 95/0 محاسبه شد. از میان فاکتورهای موثر بررسی شده در تحقیقات گذشته، سه پارامتر موثر مورد ارزیابی قرار گرفتند که عبارتند از: نسبت دبی اصلی به فرعی، نسبت عرض کانال‌ها و شیب جداره کانال‌ها. سرعت و انرژی آشفتگی نیز برای چهار شبیه‌سازی خاص مورد بررسی قرار گرفت. نتایج نشان داد که الگوی عمق آب در تلاقی دو کانال روباز به این صورت است که در وسط محل تقاطع، ارتفاع آب به حداکثر رسیده و سپس کاهش می-یابد تا در فاصله حدود یک متری از محل تلاقی، به حداقل برسد. بعد از این نقطه مجدد ارتفاع آب زیاد شده تا به تعادل برسد. درصد کاهش عمق حداقل آب به ازای تغییر هر پارامتر عبارت است از: افزایش 73/14 برابری نسبت عرض کانال‌ها تا 2/42 درصد، کاهش 11 برابری نسبت دبی تا 7/10 درصد و کاهش زاویه جداره کانال‌ها به یک سوم، تا 5/10 درصد. بر این اساس، عمده تغییرات و خصوصیات محل تلاقی دو کانال مرکب، مربوط به ویژگی‌های کانال فرعی بوده و حاصل اثریست که مومنتوم جریان فرعی بر جریان اصلی می‌گذارد.

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