مطالعه آزمایشگاهی رفتار هیدرولیکی جت‌ مستغرق عمودی، تحت تاثیر نوع شکل‌گیری و عمق استغراق

جریان جت‌های سیال مستغرق هم‌فاز با محیط، بطور عمومی تحت تاثیر پارامتر اصلی مومنتم تحلیل می‌شوند ولذا درتحلیل هیدرودینامیکی جریان آنها، مشابه عموم جریان سیال‌ها از رابطه اولر که بیان کننده روابط حاکم بر مومنتم جریان است استفاده می‌شود. از آنجایی که تغییرات سرعت جریان بیانگر میزان مومنتم آن است، پارامتر سرعت بایستی به عنوان یکی از پارامترهای اصلی در جریان جت‌ها بررسی شود. در جت‌های مستغرق به واسطه احاطه شدن جت توسط محیط هم‌فاز پیچیدگی‌هایی در معادله جریان بروز می‌نماید که شناخت آنها نیازمند مطالعه آزمایشگاهی است. در این تحقیق پروفیل‌های سرعت در جت جریان مستغرق عمودی رو به بالا و تحت تاثیر پارامترهای سرعت اولیه، نوع شکل‌گیری و عمق استغراق برروی دهانه جت مورد بررسی آزمایشگاهی قرار گرفته است. نتایج نشان داد که کارکرد هندسه خروجی جت به شکل اثرگذاری بر محدوده میدان جریان در گستره، و تسریع در رسیدن به ناحیه توسعه‌یافتگی آن است. به همین ترتیب، با افزایش واگرایی دهانه جت مقادیر سرعت میانگین در مرکز توده جت با سرعت بیشتری نزولی خواهند شد. نتایج نشان داد با افزایش واگرایی دهانه خروجی جت جریان وارده، کاهش 32 درصدی در مقادیر میانگین سرعت متوسط در نقطه شکست هسته جت از زاویه 0 تا 11 درجه مشاهده شد. همچنین افزایش میزان عمق استغراق روی دهانه جت به‌واسطه تقابل تاثیر آن بر اینرسی حرکتی جت منجر به کاهش مقادیر سرعت میانگین شد. به نحوی که با افزایش 37 درصدی عمق استغراق روی دهانه جت، مقادیر سرعت متوسط در مرکز توده جریان جت در حدود 25 درصد کاهش نشان داد.

experimental study of hydraulic behavior of vertical submerged jet under types of formation and submergence depth

the co-phase submerged jets of flow with the surrounding environment are generally analyzed under the influence of momentum parameters. therefore, in the hydrodynamic analysis of these jets, the euler equation, which describes the governing relationships of the flow momentum, is used. since the change in flow velocity represents the amount of its momentum, the flow velocity parameter is considered as one of the main parameters in the analysis of submerged flow jets. in submerged jets, due to the jet is being surrounded by a co-phase environment, complexities arise in the flow equation that require experimental studies for understanding. consequently, numerous experimental studies have been conducted on flow jets. in upward vertical submerged jets, due to the misalignment of the dominant inertial movement direction with the gravitational force, the governing equations and jet behavior differ from those of downward vertical submerged jets. therefore, in this study, the hydraulic characteristics of upward vertical submerged jets, influenced by parameters such as velocity, geometry, and the degree of submersion of the jet nozzle, have been examined by measuring the flow velocity parameter.for conducting this research, a water jet was directed through a pipe with a diameter of 110 mm, with five different flow rates ranging from 2 to 10 liters per second in 2 increments, into a plunge pool with dimensions of 1.8 * 1.2 meters and a fixed water depth of 73 centimeters. the experiments were conducted in two conditions, with initial levels of 6 centimeters and 20 centimeters above the bottom of the pool. the flow velocity measurements in all conditions were taken at levels of 23, 40, and 60 centimeters above the bottom, in the form of longitudinal profiles, using a three-dimensional velocity meter (adv). in the first condition, the measurements were solely on the mentioned jet flow without any changes to its geometry. however, in the second condition, in addition to raising the jet nozzle level from 6 centimeters to 20 centimeters above the bottom, two divergent nozzle angles of 4 and 11 degrees were also examined. data filtering to remove potential errors and data processing were performed using winadv software.for the first test case, the longitudinal velocity profiles, plotted along the axis passing through the center of the jet at different levels, were examined. the results indicate that due to the turbulent effect of the flow after exiting the jet nozzle and the effect of gravity, the flow mass undergoes dispersion, with the flow velocity initially decreasing in a relatively linear manner and then gradually decreasing exponentially, eventually flowing as a horizontal jet at the water surface. the intensity of changes in the initial sections of the curve is low, numerically ranging between 6% and 11%, and then increases to around 20% (the slope increases relatively with increasing flow rate). the shape of the velocity profiles transitions from sharp to gradually broadening as the distance from the jet nozzle increases. the measured turbulence intensities at the central axis of the jet for the tested flow rates range from 0.32 to 0.50. in the second test case, with the first measurement section closer to the jet nozzle, the measurements show that the velocity along the central axis of the jet initially moves without change relative to the jet nozzle for a certain distance before decreasing. this change in velocity along the central axis of the jet manifests as a break in the velocity graphs. by adding two divergence sections to the experiments and repeating the data collection, the velocity profiles and central axis velocities of the jet were compared in three scenarios. in the case of a 4-degree divergence angle, although the flow profile pattern is largely similar to the non-divergent case, the central axis velocities of the jet decrease. increasing the divergence angle from 4 degrees to 11 degrees shows a significant change in flow patterns and central axis velocities compared to the non-divergent condition. the turbulence intensity values are also affected by these changes in jet geometry, with turbulence intensity increasing noticeably with the divergence angle. besides the impact of jet geometry, comparing velocity values between the two test cases under non-divergent conditions, influenced by two different submersion heads at the jet nozzle, indicates that increasing the submersion head increases the collapse rate of the jet core due to the effect of the water weight in the basin on the jet nozzle. the hydraulic behavior of an upward vertical submerged jet was examined under the influence of geometric parameters of the environment, the submersion depth of the jet nozzle, and the nozzle divergence, with five different flow rates in the velocity range of 0.25 to approximately 1.25 meters per second. using adv (acoustic doppler velocimeter) for velocity measurements, the mean and oscillatory velocity profiles along the axis passing through the center of the jet were analyzed. the analysis shows that increasing the submersion depth of the nozzle leads to an increased collapse rate of the jet core. quantitatively, this impact results in a 20% to 25% reduction in mean velocity values at the central core of the jet for approximately a 37% increase in submersion head. additionally, the results indicate that increasing the divergence from 0 to 4 degrees reduces mean velocity values by about 25%, and for a divergence angle of 11 degrees, the reduction in average velocity at the jet core’s breakdown point is about 32% compared to the normal condition.