بررسی عددی جریان در فرآیند گذار از نقطه کارکرد بهینه به بار بیشینه در توربین فرانسیس

نوع مقاله : گرایش پیشرانش و انتقال حرارت

نویسندگان

1 دانشجوی کارشناسی ارشد، دانشکده مهندسی دریا، دانشگاه دریانوردی و علوم دریایی، چابهار، ایران

2 نویسنده مسئول: استادیار، دانشکده مهندسی دریا، دانشگاه دریانوردی و علوم دریایی، چابهار، ایران

3 استادیار، دانشکده مهندسی دریا، دانشگاه دریانوردی و علوم دریایی، چابهار، ایران

چکیده

جریان در درفت‌تیوب توربین‌های آبی در نقطه کارکرد بار بیشینه با ناپایداری‌های زیادی همراه می‌باشد. علاوه بر افت راندمان ناشی از شکست گردابه، نوسانات فشاری فرکانس پایین ناشی از آن می‌تواند موجب پدیده تشدید شده و عمر توربین را کاهش دهد. در پژوهش حاضر فرآیند تشکیل هسته گردابه بار بیشینه (مشعل) در گذار از نقطه کارکرد بهینه به بار بیشینه موردمطالعه قرارگرفته و رژیم‌های گذرای تشکیل‌شده حین این فرآیند گذار موردبحث و مطالعه واقع‌شده‌اند. مشخص می‌شود که هسته گردابه مشعل نتیجه پدیده شکست گردابه حبابی بوده و عامل اصلی آن نیز تشکیل نقطه سکون و ایجاد جریان بازچرخشی در محور درفت‌تیوب است. این جریان بازچرخشی به دلیل افت مومنتوم محوری در ناحیه مخروطی درفت‌تیوب ایجاد می‌شود. نتایج هسته گردابه نشان می‌دهد که در مراحل رشد و تشکیل هسته گردابه مشعل، ابتدا قطر هسته پایه بار بهینه رشد می‌کند. سپس در سطح ساختار هسته گردابه امواجی ایجاد خواهند شد که با گذشت زمان و قدرت گرفتن چرخش در میدان جریان، ساختار یکپارچه هسته را گسسته و به چندین بخش تقسیم خواهد شد. سپس قطر و طول ساختار هسته گردابه افزایش‌یافته و بخش‌های زیادی از مقطع عرضی درفت‌تیوب را تحت تأثیر قرار می‌دهد، طول این ساختار تا دیفیوزر درفت‌تیوب پیشروی خواهد داشت. ازاین‌رو، مشخص می‌شود که محل اصلی اثرگذاری مشعل، انتهای ناحیه مخروطی و ورودی زانویی درفت‌تیوب است. با بررسی نتایج عددی مشخص گردید با گذشت 5/1 تا 2 ثانیه پس از شروع فرآیند گذار تغییرات چشمگیری در مؤلفه‌های سرعت دورانی، محوری و شعاعی به وجود خواهد آمد.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Numerical Investigation of the Transition Process from the Optimal Operating Point to the Maximum Load of the Francis Turbine

نویسندگان [English]

  • Aliasqar Haqani 1
  • Mohammad Reza Negahdari 2
  • Seyed Amin Hosseini 3
1 M.Sc. Student, School of Marine Engineering, Chabahar Maritime University, Chabahar, Iran
2 Corresponding author: Assistant Professor, School of Marine Engineering, Chabahar Maritime University, Chabahar, Iran
3 Assistant Professor, School of Marine Engineering, Chabahar Maritime University, Chabahar, Iran
چکیده [English]

The flow in the draft tube of water turbines at the point of maximum load operation is associated with many instabilities. In addition to the loss of efficiency caused by the vortex breakdown, the resulting low frequency pressure fluctuations can cause the resonance phenomenon and reduce the life of the turbine. In the current study, the process of forming the maximum load vortex core (torch) in the transition from the optimal operating point to the maximum load has been studied and the transient regimes formed during this transition process have been discussed and studied. It is clear that the core of the torch vortex is the result of the bubble vortex breaking phenomenon and its main factor is the formation of a stagnation point and the creation of a recirculation flow in the axis of the draft tube. This recirculation flow is created due to the loss of axial momentum in the conical region of the draft tube. The results of the vortex core show that in the stages of growth and formation of the burner vortex core, the core diameter of the optimal charge base grows first. Then, waves will be created on the surface of the vortex core structure, which with the passage of time and the strength of the rotation in the flow field, will break the integrated structure of the core and will be divided into several parts. Then the diameter and length of the vortex core structure increases and affects many parts of the draft tube cross-section, the length of this structure will progress to the draft tube diffuser. Therefore, it is clear that the main place of effect of the torch is the end of the conical area and the elbow inlet of the draft tube. By examining the numerical results, it was determined that with the passage of 1.5 to 2 seconds after the start of the transition process, there are significant changes in the rotational, axial and radial velocity components to will exist.

کلیدواژه‌ها [English]

  • Water turbines
  • Vortex Breakdown
  • The process of transition of work point
  • Optimal load
  • Maximum load

مراجع

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مکانیک هوافضا
دوره 20، شماره 3 - شماره پیاپی 77
شماره پیاپی 77، فصلنامه پاییز
آذر 1403
صفحه 107-126

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سابقه مقاله

  • تاریخ دریافت: 03 تیر 1403
  • تاریخ بازنگری: 26 مرداد 1403
  • تاریخ پذیرش: 27 شهریور 1403
  • تاریخ انتشار: 01 آذر 1403

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