تاثير شكل ديواره‌ي تبديل هاي واگرا در خصوصيات پرش هيدروليكي

The Effect of Shape of Walls of Expansions on the Characteristics of Hydraulic Jump

پرش هيدروليكي يكي از مهم ترين پديده ها در جريان متغير سريع است، كه مورد توجه مهندسان هيدروليك است. در اين مطالعه با توجه به اهميت بالاي اين پديده در علم هيدروليك، خصوصيات هيدروليكي پرش تشكيل‌يافته در تبديل هاي واگرا با 3 شكل ديواره‌ي s- شكل، مستقيم، و انحنادار به ازا 5 عدد فرود مختلف در بازه‌ي 1/9 < Fr1 < 8/5 بررسي شده است. بدين منظور مقادير عمق و سرعت در نقاط مختلف پرش هيدروليكي در تبديل ها برداشت شده است.. پس از تحليل نتايج، مقادير بيشينه و كمينه‌ي سرعت و طول پرش و از سوي ديگر، عمق پرش به ترتيب در تبديل هاي انحنادار و s- شكل مشاهده شده است. مقادير به‌دست‌آمده از تبديل با ديواره‌ي مستقيم نيز در بازه‌ي مقادير دو تبديل ديگر واقع شده است. نتايج نشان داده است كه به ازا طول ثابت ديواره‌ي تبديل، انحناي ديواره ها باعث كاهش تدريجي سرعت و در نتيجه كاهش نرخ استهلاك انرژي در پرش هيدروليكي مي شود.

Hydraulic jump is one of the most important phenomena in rapid varied flow. Considering the importance of this phenomenon in hydraulic science, in the present study, hydraulic features of the formed jump in expansions with three shapes of S-shaped, straight, and curved, for five Froude numbers of 5.8 < Fr1 < 9 were investigated. So, the values of depth and velocity in different points of hydraulic jump were measured. It should be noted that the values of instantaneous velocity in 5 vertical directions and with length intervals of 30 cm in experimental model were measured. The measured velocity profiles indicated that in all three transitions, the values of velocity increased as they were getting away from the bed and after getting to the maximum values of velocity reduced. The main cause of the mentioned phenomenon is the extreme combination of water and air near to the surface of water at the time hydraulic jump. After the analysis of the obtained data, values of maximum and minimum of velocity and length of jump were observed in curved and S-shaped expansions, respectively. On the other hand, the values of maximum and minimum of secondary depth of the jump were observed in curved and S-shaped expansions. The measured values from expansions with direct walls were between the values of the two other expansions. In curved expansions due to the curvature of the walls and gradual increase of the width of the canal at the time of hydraulic jump less combination of water and air occurred than the two other expansions. Therefore, the reduction of velocity in curved expansion was less than the two other expansions. Furthermore, in S-shaped expansions due to the sudden increase in the width of the channel, the values of combination of water and air was higher so that the highest values of velocity reduction near the surface of water occurred in this expansion. The results of the study showed that for the fixed length of the wall of expansions, the curvature of the walls causes gradual reduction of velocity and it leads to the reduction of rate of energy dissipation in hydraulic jump.