عنوان مقاله
محاسبه جریان متلاطم ناپایدار در کمپرسور محوری: مقایسه RAN ها و LES بوسیله آزمایش
فهرست مطالب
مقدمه
ابزار و روش ها
تاثیر تراکم شبکه بر روی محاسبات LES
تاثیر شبیه سازی تلاطم بر روی محاسبات URANS
مقایسه با داده های تجربی
نتیجه گیری
بخشی از مقاله
وضعیت های مرزی
یک وضعیت تزریق همراه با پارامترهای داده های تجربی در دهانه بکار گرفته شده است. برای کاهش هزینه های محاسبات، چهار پایه در راس و پایین کمپرسور جا نیوفتاده اند. تاثیر آن ها بر روی دهانه بوسیله ی تراکم تلاطم در مجرا مورد لحاظ قرار می گیرد. متاسفاته اطلاعاتی در مقیاس طول تلاطم ها در آزمایشات در دست نیست. برای LES، وضعیت مرزی بر روی نسخه ساده شده روش جریان متلاطم ترکیبی متمرکز می شود که آشفتگی هایی را در جریان نشان می دهد که تاثیرات تلاطم را شبیه سازی می کنند.
کلمات کلیدی:
Prediction of the unsteady turbulent flow in an axial compressor stage. Part 1: Comparison of unsteady RANS and LES with experiments Nicolas Gourdain ⇑ CERFACS, Computational Fluid Dynamics Team, Toulouse, France ISAE, Dpt. of Aerodynamics, Energetics and Propulsion, Toulouse, France article info Article history: Received 15 September 2013 Received in revised form 3 September 2014 Accepted 30 September 2014 Available online 20 October 2014 Keywords: Large-Eddy Simulation Unsteady RANS Compressor stage abstract A better understanding of turbulent unsteady flows is a necessary step towards a breakthrough in the design of modern gas turbine components. With the increase in computing power, LES emerges as a promising method to improve both knowledge of complex physics and reliability of flow solver predictions. However, there is still a lack of evidences in the literature that LES is applicable for turbomachinery at conditions relevant to industrial applications. In that context, the objective of the present work is to investigate the capability of LES to predict the turbulent flow in a stage of an axial compressor and compare the results with unsteady RANS data and experiments. The compressor operates at industrial relevant conditions, with Mach and Reynolds numbers equal to M ¼ 0:5 and Re ¼ 7 105 , respectively. This paper presents the numerical method and a comparison of URANS and LES results to experimental data. A particular care is brought to estimate the results sensitivity to grid refinement (LES) and to turbulence and transition modelling (URANS). The comparison to experiments shows that LES better predicts time-dependent quantities than URANS, especially close to the casing. However, both URANS and LES fail to accurately estimate the compressor performance (efficiency and pressure ratio). 2014 Elsevier Ltd. All rights reserved. 1. Introduction The design of efficient gas turbines requires a better prediction of the components performance and understanding of unsteady flows. Among all components, the compressor remains a critical part of a gas turbine, especially regarding its efficiency and stability. Due to the adverse pressure gradient, the flow in this component is unstable by nature and complex flow instabilities such as surge or rotating stall can occur [10], potentially leading to mechanical failure. In that context, maximizing the efficiency of compressors is particularly complex. First, overall performance is largely impacted by the matching conditions between the successive rotor and stator rows (‘‘time-averaged’’ flow effects). For instance, rotor tip clearance variations and end-wall flows affect both efficiency [12] and aerodynamic stability [9,26]. Then, relative motions between fixed and rotating parts induce periodic unsteady flows that also modify overall performance, aerodynamic stability and the development of secondary flows [2,3]. The improvement of the compressor robustness and performance (for example by using control devices in the tip leakage region [24]) requires thus a better understanding of the flow physics that takes place in these systems.
