توسعه رابطه‌اي جهت تعيين فاصله بين هواده اول و دوم سرريز شوت بر اساس غلظت هواي مينيمم (مطالعه موردي سد آزاد كردستان)

افزايش روز افزون جمعيت به همراه تقاضاي بيشتر براي آب در بخش‌هاي كشاورزي و نيرو، رشد سريع ساخت سدها را به همراه داشته است. در اين ميان افزايش ارتفاع سدها به منظور افزايش ذخيره مخزن و برآورد نياز آب، موجب افزايش سرعت آب روي سرريزها مي‌گردد كه به دنبال آن نياز به بررسي كاويتاسيون و راهكارهاي مقابله و يا كاهش خسارات آن اجتناب ناپذير مي‌باشد. طبق بررسي‌هاي صورت گرفته در دهه‌هاي اخير ساده‌ترين، اقتصادي‌ترين و مؤثرترين راهكار جهت كاهش و جلوگيري از اين آسيب‌ها، تعبيه‌ي هوادهنده‌ها در مكان‌هاي مناسب و وارد نمودن هوا به جريان مي‌باشد. لذا در اين تحقيق بااستفاده از 1200 داده تجربي حاصل از 90 آزمايش صورت گرفته توسط Pfister (2007) رابطه‌اي جهت تعيين روند خروج هوا از جريان تحت شرايط فشار حفره صفر و ضريب همبستگي بيش از 84/0 به عنوان تابعي از طول بي‌بعد شده‌ي جت جريان با استفاده از تحليل رگرسيوني ارايه شده است كه با توجه به سادگي با دقت مناسب مي‌تواند در تعيين فاصله بين هواده‌ها بر اساس حداقل ميزان غلظت هواي بستر مورد استفاده قرار گيرد. نتايج مطالعه حاضر با فواصل مربوط به هواده‌هاي سرريز سد آزاد بر اساس غلظت هواي بستر مينيمم مورد بررسي قرار گرفته است.

The increase of population and demand for water, agriculture and energy cause rapid increase construction of the dam has been. Moreover, the increase of dam height to increase storage and estimate the need for water cause increase the velocity of water over the spillway has been. Spillways, chutes and bottom outlets are important hydraulic structures for dam safety. Due to high velocities combined with low pressures, cavitation damages may occur on chute bottom and cause major damages or endanger the dam stability. Damage experience for flows in spillway tunnels and chutes indicates that damage becomes significant when water velocities exceed 30m/s, this velocity or head can be considered as the borderline for high velocity or high head flows. Introducing air to high-speed flow is necessary to prevent pressure reduction and its events such as cavitation. It is possible to protect spillway surfaces from cavitation damages using aerator devices. Usually, the air entering the flow is not reached to the bed chute. It is necessary to install the first aerated according to topographic conditions and cavitation index at the appropriate location. By determining the process of changing the air concentration of the bed, the distance between the two aerators can be determined. The air in the flow causes the compression and damping that cause Bursting bubbles. In result, the damage caused by cavitation is reduced. So cavitation investigations will be necessary and need to reduce and prevent cavitation damages. The length of the flow jet has a fundamental role in determining the distance between two aerators. With increases the length of the jump, the contact surface of the upper and lower layers of the jet is in more contact with the air and affects the amount of air entering the flow. The absorbed air is removed from the flow after the Jet collision. By determining the minimum concentration of air in the bed, an optimal distance between the two aerations can be selected to prevent cavitation damage. selec‎t the minimum air concentration of bed is based on the relationship provided by Wood (1983). It means that the concentration of average air in the stream is higher, which causes the flow of bulking and requires taller walls for the sides of the shut Which is not economically feasible. The variation in the air concentration of the bed can only be considered as a function of the length of the jump flow and the upstream heights. Creating a suitable duct for providing A negative cavity pressure Lead to better performance that causes increases the distance between aeration. So use of aerators in suitable places and the entrance of air to water flow is a most effective way to reduce this damage, therefore in this study, an equation has been derived to estimate the distance between two aerators base on 1200 data of 90 experiments with R2 more than 0.84. Results of the present study with distance aerators of the Azad dam based on the minimum air concentration of bed have been compared and investigated