عنوان مقاله
موتور راکت با خرج ستاره ای – بالیستیک داخلی ناپایدار
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فهرست مطالب
چکیده
مقدمه
مدل عددی
پیش بینی شبیه سازی
ملاحظات پایانی
بخشی از مقاله
پیش بینی های شبیه سازی
شکل هندسی خرج ستاره ای دارای دو بسامد تشدید اصلی می باشد، یکی برای پیک ستاره در حدود 4200 Hz و یکی در ناوه در حدود 14000 Hz. استفاده از بسامد طبیعی پائین به عنوان بسامد تشدید اصلی در مدل میرایی یا دامپینگ، باعث میرایی درست پیک خرج ستاره ای و میرایی زیاد ناوه خرج ستاره ای می شود.
به منظور حفظ مقدار درست و همسان میرایی در سرتاسر مقطع، به گونه ای که سیستم بنا به انتظار به نسبت میرایی معلوم پاسخ می دهد، ثابت میرایی الگوریتمی که نوسانات بسامد بالاتر را فیلتر می کند، تا حدی افزایش می یابد تا بدین طریق به میرایی ارتعاشات بسامد بالاتر در ناوه خرج ستاره ای کمک شود.
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کلمات کلیدی:
Aerospace Science and Technology 8 (2004) 47–55 www.elsevier.com/locate/aescte Star-grain rocket motor – nonsteady internal ballistics Sonny Loncaric, David R. Greatrix ∗ , Zouheir Fawaz Department of Aerospace Engineering, Ryerson University, Toronto, Canada M5B 2K3 Received 20 December 2002; received in revised form 2 June 2003; accepted 9 September 2003 Abstract The nonsteady internal ballistics of a star-grain solid-propellant rocket motor are investigated through a numerical simulation model that incorporates both the internal flow and surrounding structure. The effects of structural vibration on burning rate augmentation and wave development in nonsteady operation are demonstrated. The amount of damping plays a role in influencing the predicted axial combustion instability symptoms of the motor. The variation in oscillation frequencies about a given star grain section periphery, and along the grain with different levels of burnback, also influences the means by which the local acceleration drives the combustion and flow behaviour. 2003 Elsevier SAS. All rights reserved. Keywords: Solid rocket motor; Star grain; Internal ballistic modeling; Structural vibration; Combustion instability 1. Introduction Symptoms commonly attributed to axial combustion instability in solid-propellant rocket motors (SRMs) include the formation of a sustained limited-amplitude oscillating axial compression wave in the core flow, with an associated dc shift in base pressure in some cases. Earlier experimental findings reported in [12] illustrate that axial combustion instability symptoms can occur under certain conditions where it is evident that the motor structure influences this behaviour. Using a numerical simulation model for cylindricalgrain SRMs, predicted results in [11] illustrated the potential for explicit coupling between structural vibrations and nonsteady internal ballistic behaviour, independent of any other instability driving mechanism (e.g., augmented frequency-dependent pressure- or velocity-coupled combustion response as commonly applied by combustion instability researchers [15]; in more complex grain geometries, e.g., with segmented propellant sections, vortex shedding is also being investigated as a driving mechanism of axial wave symptoms [15]). Greatrix [6–8] has shown that both steady and unsteady acceleration fields can significantly affect the burning rate of the solid propellant. This augmentation of the burning rate can play a key role in pressure wave development * Corresponding author. E-mail address: greatrix@acs.ryerson.ca (D.R. Greatrix). within the motor chamber. The influence of the structural vibrations and the unsteady acceleration fields they create in the motor are thus of importance. However, nonsteady accelerations are more difficult to analyze for star-grain or other non-cylindrical configurations that are common in SRM applications, and a more sophisticated numerical model must be utilized. This investigation involves the analysis and prediction of the nonsteady internal ballistics of a star-grain SRM. The need to include structural vibration within the framework of an internal ballistic simulation model is made evident through observations from previous cylindrical- and stargrain rocket motor research [11,12]. Changes in motor structure (e.g., propellant grain configuration, surrounding wall thickness and material properties) are observed to result in changes in combustion instability symptom profile characteristics (e.g., dual-axial-wave systems vs. singlewave) and magnitude (e.g., dc rise). 2. Numerical model The numerical model is comprised of two parts or modules – the internal ballistic flow (IBF) and the structural finite element (SFE) module. The IBF model is quasi-onedimensional in nature, while the SFE module uses a series of two-dimensional finite element (FE) sections placed on the nodes of the IBF grid along the long axis of the motor (refer to Fig. 1). Although the sections are independent of 1270-9638/$ – see front matter 2003 Elsevier SAS. All rights reserved. doi:10.1016/j.ast.2003.09.001
