شبيه سازي عددي تاثير امواج بر گرداب هاي شكل گرفته در آبگيرقائم

گرداب را مي­توان به عنوان يكي از پديده هاي ناشناخته در زمينه آبگيري از مخازن سدها نام برد كه مي­تواند باعث به وجود آمدن مشكلاتي در فرآيند آبگيري شود. در اين تحقيق با هدف بررسي تاثير امواج در سطح مخزن بر گرداب، به شبيه­سازي عددي امواج در دهانه آبگيرهاي قائم با استفاده از نرم­افزار STAR-CCM، در شرايط تشكيل گرداب­هاي مختلف پرداخته شده است. در همين راستا گرداب­هاي كلاس A، B و C در مدل عددي شبيه­سازي گرديد و نتايج آن پس از برخورد با امواج بررسي شد. نتايج نشان داد كه امواج باعث كاهش مولفه­هاي سرعت مماسي، شعاعي و محوري گرداب شكل گرفته مي­شوند. طبق نتايج ارائه شده، ماكزيمم مقدار مولفه سرعت مماسي در هنگام حضور امواج به طور ميانگين در گرداب­هاي نوع A، B و C به ترتيب حدود 14%، 19% و 23% كاهش داده شده است. ميزان كاهش ماكزيمم مقدار مولفه سرعت شعاعي نيز براي گرداب­هاي كلاس A، B و C به ترتيب حدود 9%، 13% و 18% مي­باشد. ماكزيمم مقدار سرعت محوري نيز براي گرداب­هاي كلاس A، B و C به ترتيب حدود 15%، 16% و 23% كاهش داده شده­اند. با توجه به نتايج شبيه­سازي، ميزان كاهش با كم شدن دامنه امواج بيشتر شده و اين بدين معني است كه امواج با دامنه كوچكتر يا به عبارتي ريزموج­ها بهتر مي­توانند مولفه­هاي سرعت را كاهش داده و در نتيجه جريان گردابي را به روشي هيدروليكي تضعيف كنند.

The formation of a vortex at the mouth of power plant intake is one of the unfavorable hydraulic phenomena that occur during dewatering of dams. More precisely, the formation of vortex flows in the openings of the intake disturbs the proper functioning of the intake structure. vortices cause problems such as oscillating in the system, reducing turbine output, increasing hydraulic losses in the intake openings, entering the air and particles into the intake pipe and eventually reducing its efficiency. In recent years, various scholars have conducted extensive studies on the phenomenon of vortex. In the meantime, research has been carried out experimentally using mechanical devices and less attention has been paid to the natural phenomena existing on the level of reservoirs of dams and their impact on the vortex. One of the most important natural phenomena that occurs in the reservoir of dams is the waves that can affect the vortex. In this research, with the aim of investigating the effect of waves on the vortex, numerical simulation of waves in the openings of vertical intake has been studied in various vortex formation conditions. In this regard, three class of vortices A, B and C were simulated in numerical model and the results were investigated after dealing with waves. To simulate the flow in the vertical intake, the model designed by Sun and Liu was used. This model is designed in a cylindrical shape with four rectangular inlets, with a vertical intake located at the center and end of the cylinder. In the present study, the model was studied in three-dimensional and two-phase mode, so that numerical simulation of vortex and wave can be investigated with this approach. In order to reduce the computational time to solve the equations, Euler's method was chosen and the turbulence was simulated using the LES model in STAR-CCM Software. After sensitivity analysis, 3 mm grid dimensions were selected. For computational mesh domain, a Cartesian coordinate was used and the free surface was considered using the VOF method. Accordingly, after formation of three classes of vortices A, B and C in the numerical model, three waves with a/d ratio of 2.6%, 1.3% and 0.3% were generated and the effect of their collisions on vortices was analyzed. The amplitudes of the waves are determined in relative proportions of the reservoir water's height and are not far from reality. The results showed that the waves reduced the components of tangential, radial and axial velocity. According to the results, the maximum component of the tangential velocity at the time of the presence of waves is reduced by about 14%, 19% and 23%, respectively, in the class A, B, and C vortices. The radial velocity component is also reduced by about 9%, 13% and 18% for the A, B, and C vortices, respectively. The maximum axial velocity was also reduced to 26%, 13%, and 23% for class A, B, and C vortices, respectively. According to the simulation results, the decrease rate with decrease decreasing wave amplitude, which means that smaller waves can lower the velocity components and thus weaken the vortex flow.