بررسي نوسانات فشار و نيروي عكس‌العمل سطح در حوضچه‌هاي آرامش شيب‌شكن‌هاي مجهز به مستهلك‌ كننده‌هاي شياري و شبكه‌اي

Hydraulics of Flow in Stilling Basins with Vertical Drops Using Grating and Netting Dissipators

در اين مقاله به ارايه نتايج مدل‌سازي تحليلي و آزمايشگاهي در خصوص تعيين توزيع فشار و نيروي عكس‌العمل سطح در حوضچه‌هاي آرامش شيب‌شكن‌هاي مجهز به مستهلك‌كننده‌هاي شياري و شبكه‌اي پرداخته مي‌شود. اين نوع مستهلك‌كننده‌ها به منظور افزايش راندمان استهلاك انرژي در شيب‌شكن هاي احداثي در شبكه‌هاي آبياري و زهكشي پيشنهاد مي‌شوند. بررسي نتايج نشان مي‌دهد كه در شيب‌شكن با مستهلك كننده شياري هرچه عرض شيار ها كمتر باشد، دامنه نوسانات فشار در بستر پايين دست بيشتر است و با افزايش دبي، دامنه نوسانات افزايش مي‌يابد. ضمناً ميزان نوسانات فشار در شيب شكن با مستهلك كننده شياري نسبت به مستهلك كننده شبكه اي كمتر است. توزيع فشار در بستر پايين دست شيب‌شكن با مستهلك كننده ي شبكه‌اي به صورت نوساني است و با ثابت نگه داشتن بعد عرضي شبكه ها با افزايش دبي و كاهش بعد طولي شبكه ها تعداد نقاط حداكثر و حداقل فشار افزايش مي يابد.

Abrupt change in the channel bed elevation in the hydraulic systems tends to create a severe flow kinematic energy. This excess energy results in different unfavorable phenomena including tremendous forces on hydraulic structures, scouring and degrading the channel bed which results in the destruction of the downstream structures. These phenomena would intensify while a number of vertical drops constructed consecutively along the channel. The main goal of the present study is to explore methods for increasing the energy dissipation efficiency of vertical drops by installing new types of dissipators, namely Grating and Netting drop-type dissipators based on the analytical/experimental modeling. These types of dissipators could be established over the drop crest looking like a bottom racks. In addition, the features of pressure distribution along the pool and reaction force over the pool floor were investigated. By assembling the above mentioned structures over the stilling basins of vertical drops, the jet flow direction is changed and the degree of turbulence increases and as a result there is an increase in the head loss. The enhanced efficiency of the proposed structures was quantified based on the experimental data obtained in this study. Both analytical and experimental investigations were performed in the present study. Based on the model experimentation data, empirical equations were presented to estimate the force acting on the basin floor. The proposed semi-analytical model compared well with the experimental results. However, there are small discrepancies between the analytical and experimental results of netting dissipators. This is partly due to the flow high turbulence and complicated phenomena existed in the stilling basins of netting dissipators. Also, the air bubble entrainment is another source of the difference between the two sets of results.