پديد آورندگان :
فتحعلي، حسام دانشگاه بين المللي امام خميني قزوين - دانشكده فني و مهندسي - گروه مهندسي عمران , مهاجري، حسين دانشگاه خوارزمي - دانشكده فني و مهندسي - گروه مهندسي عمران , كيلانه ئي، فواد دانشگاه بين المللي امام خميني قزوين - دانشكده فني و مهندسي - گروه مهندسي عمران , فاضلي، ميثم دانشگاه آزاد واحد علوم و تحقيقات، تهران - دانشكده عمران ، هنر و معماري - گروه مهندسي عمران آب
كليدواژه :
بستر شني , كانال روباز , جريان آشفته , مدلسازي عددي , جريان كم عمق
چكيده فارسي :
يكي از چالشي ترين مباحث هيدروليكي، بررسي جريان غيرسيلابي با استغراق نسبي پايين (نسبت عمق آب به ابعاد زبري بستر پائين) و با اعداد
رينولدز بالا در رودخانه هاي كوهستاني با بسترهاي شني مي باشد. مطالعه حاضر به بررسي عددي اين نوع جريان در مقياس سنگدانه ها
به صورت فيزيك ي، علاوه بر مدلساز ي هيدروليكي Flow3D پرداخته است . به اين منطور بستر شني توسط وارد نمودن مدل رقومي در نرم افزار
از طريق اعمال ضريب زبري ، مدل گرديده شد. پس از صحت سنجي و در پايان مدل ساز ي، نتايج ن شان دا د كه وجود ب ستر شني در اين شرايط،
علاوه بر ميدان جريان، بر شدت آشفتگي و تنش برشي بستر به شدت اثر ميگذارد. بررسي كمي ناحيه تحت تاثير سنگدانه هاي شني، نشان داد كه
محدودهي لايهي زبر-ناحيه مت شكل از زيرلايه لزج و ناحيه بين نابيني در ب سترهاي زب ر- نه تنها در مكان تغيير مينمايد، بلكه برا سا س پارامترهاي
0 عمق جريان تغيير مينماي د. چنين مشاهدهاي تعريف دقيق و جامع اين ناح يه را / 0 تا 2 / آشفتگي مختلف مورد مطالعه نيز اين محدوده از 08
بس يار مشكل و پيچيده مينمايد. همچنين بررس ي تغييرات سرعت طولي و متوسط انرژي جنبشي آشفتگي حاكي از تشكيل رگه هاي طولي تغييرات
سرعت و انرژي جنبش ي در عرض كانال ميباشد . با وجودي كه اين رگه ها با عمق جريان مقياس ميشدند، با توجه به نوع مدلساز ي آشفت گي در
مطالعه حاضر ، تشك يل اين رگه ها به در هم تنيده شدن گردابه ها و دنباله هاي تشك يلي در اطراف سن گدانه هاي ش ني تش كيل دهنده بستر نسبت داده شد. در نهايت با بررسي شكل كانتورها ي سرعت برش ي در كف كانال اين نتيجه حاصل گر ديد كه بيشت رين سرعت برش ي در نزديكي مرتفع ترين سنگدانه تشگيل ميگردد كه ميتواند تا 5 برابر بزرگتر از مقدار متوسط سرعت برشي باشد.
چكيده لاتين :
The study of mountainous river flow in natural condition where the relative submergence (the ratio of water
depth to the bed roughness length characteristics) is low and Reynolds number is too high is one of the most
challenging hydraulic topics. Indeed, most of the rivers that cross the mountainous areas are covered with
coarse aggregates such as gravel. In natural conditions, usually water depth is not high and consequently
existence of roughness can affect the whole of the flow field and velocity profile specially in the roughness
sublayer. Investigation of flow field in this type of rivers and understanding the important parameters of
turbulent flow helps to better understand the behavior of such rivers. In shallow currents, the relative
submergence is often less than 20. However, there is an uncertainty regarding this range. In the present study,
the flow structure intermediate submerged flows has been numerically investigated. For this purpose, the
gravel bed was modeled physically by importing a digital elevations model of the laboratory artificial bed into
the Flow-3D software. One of the innovations of this research was the importing of a rough bed in a physical
manner while in similar researches, the roughness equivalent coefficient was imported as an effective
roughness parameter and the bed was not physically modeled. Furthermore, in present study, the study of parts
of the flow in numerical simulation order that in laboratory study Due to laboratory limitations was not
investigated, was considered. Actually, the main purpose in present study is investigation of turbulent flow
characteristics in a low relative submergence in near sandy stone. One of the other points of this research is
the investigation of low relative submergence, while most studies had done on high relative submergence. It
should be noted, for simulating the k-ԑ RNG that is two equations model and having Medium computing cost,
has been used in Flow-3D Software. According to the results, it was found that Flow-3D is able to simulate
these types of flows. After validation and at the end of modeling, it was found that existence of gravel particles
in these conditions affects severely the flow field, turbulent intensity and shear stress. Quantitative
investigation of region under sandy sandstone shows that roughness sublayer region not only changes in
location, but also vary according to the parameter being studied. Such an observation makes the region's
precise and comprehensive definition very difficult and complicated. also existence of changes in longitudinal
velocity and medium turbulent kinetic energy (T.K.E) is the cause of formation of longitudinal strings of
variations in velocity and kinetic energy across the channel. According to the type of turbulent modeling in
this study which was k-ԑ RNG, existence this strings Attributed to Swirling together and Arranged sequences
near sandy sandstone because these model Based on isotropic turbulence assumption and it hasn’t ability to
investigating and modeling the secondary currents. Finally with investigation of shear velocity contours in bed
channel, it was found that maximum shear velocity occurred near maximum elevation sandstone. Also,
maximum drag force occurred in this region. Finally, due to small flow fields in near of walls and colliding
Flow currents to these walls, the mean of shear velocity and friction increases.
