بررسی عددی اثرات کاهش لحظه‌ای سطح مقطع یک دیفیوزر خروجی گاز مافوق‌صوت

نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه پژوهشی پیشران/پژوهشکده سامانه های حمل ونقل فضایی/ پژوهشگاه فضایی ایران، تهران/ایران

2 کارشناسی ارشد، مهندسی مکانیک، پردیس دانشکده‌های فنی، دانشگاه تهران، تهران، ایران

3 پژوهشکده‌ سامانه‌های حمل و نقل فضایی، تهران، ایران

چکیده

تحقیق پیش‌رو به‌منظور بررسی تاثیر رسوب‌گرفتگی در عملکرد دیفیوزر مافوق صوت تست استند خلاء انجام شده است. گرفتگی مجرا با رسوب اکسید آلومینیوم به صورت تنگ‌شدن تدریجی و وابسته به زمان در شبیه‌سازی عددی لحاظ شده است. در شرایط اولیه، جریان مافوق‌صوت در نازل و دیفیوزر برقرار است. با گذشت زمان، سطح مقطع دیفیوزر با استفاده از روش شبکه‌ی متحرک کاهش داده می‌شود. در تحلیل عددی جریان تراکم‌پذیر به‌صورت دوبعدی و تقارن‌محوری است و از مدل آشفتگی انتقال تنش برشی k-ωبرای حل میدان جریان استفاده شده است. تنگ‌شدگی مجرا (n) برابر با نسبت قطر لحظه‌ای گلوگاه ثانویه دیفیوزر به قطر اولیه‌ی آن تعریف شده است. بررسی‌ها نشان می‌دهد که با تغییر پارامتر n از مقدار 1 تا 75/0، جدایش جریان از روی دیواره دیفیوزر به تعویق می‌افتد و با کاهش افت فشار کل، بازده بازیابی فشار استاتیک جریان توسط دیفیوزر افزایش می‌یابد. با افزایش میزان تنگ‌شدن مجرا از 75/0n= تا 64/0n= در اثر خفگی جریان در گلوگاه ثانویه، موقعیت و ساختار امواج ضربه‌ای جریان در دیفیوزر دچار تغییرات اساسی شده و جدایش جریان در نزدیکی ورودی دیفیوزر و یا در داخل نازل رخ می‌دهد. در این شرایط، دیفیوزر از حالت راه‌اندازی خارج شده و محفظه‌ی تست از شرایط خلاء خارج می‌شود.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Numerical Analysis of Cross Section Time Variation Effects of the Supersonic Exhaust Diffuser

نویسندگان [English]

  • Nematollah Fouladi 1
  • Mohsen Hataminasab 2
  • Sina Afkhami 3
1 Space Transportation Research Institute, Iranian Space Research Center, Tehran, Iran
2 School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran
3 Space Transportation Research Institute, Iranian Space Research Center, Tehran, Iran
چکیده [English]

This paper is presented to investigate the deposition effect on a second throat exhaust diffuser performance. In the numerical simulation, the blockage of the diffuser due to the deposition of aluminum oxide is considered by a gradual and time-dependent cross-section constriction. In the initial conditions, the supersonic flow has been established in the nozzle and diffuser. Diffuser cross-section area is reduced by using a dynamic mesh method during the solution. The flow is considered compressible, viscous, and 2 dimensional axis-symmetric. The k-ω shear stress transport turbulence model is used to solve the turbulent flow field. Diffuser blockage (n) is equal to the ratio of instantaneous and primary diameters of the second-throat. By changing the value of n from 1 to 0.75, the onset of flow separation is moved to the downstream location in the diffuser. This results in a considerable reduction of total pressure loss and then improves the flow pressure recovery. Decreasing parameter n from 0.75 to 0.64, the flow structure is subjected to severe changes and the separation of the flow occurs near the diffuser inlet or inside the nozzle. In this condition, the diffuser state changes from starting to un-starting mode. Therefore, the vacuum condition vanishes in the test chamber.

کلیدواژه‌ها [English]

  • Second-throat Diffuser
  • numerical simulation
  • Aluminum oxide deposition
  • Instantaneous cross section
  • Dynamic Mesh Method
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