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در این پژوهش روشی خودکار برای بهینه سازی ردیف پره ی استاتور و روتور توربین جریان محوری معرفی می شود. در این روش الگوریتم ژنتیک، مولد هندسه، ایجادکننده ی شبکه ی محاسباتی و حل کننده ی میدان جریان به هم مربوط شده اند. تابع هدف در نظر گرفته شده عبارت است از تلفات فشار کل جریان در عبور از ردیف پره ی استاتور و روتور توربین، و نیز با استفاده از تغییر توزیع ضخامت ردیف پره های موجود، تعداد محدودی پارامتر طراحی منظور و وارد الگوریتم بهینه سازی می شود. با استفاده از قابلیت های نرم افزار تحلیل میدان جریان، شبکه ی ساختاریافته به صورت سه بعدی ایجاد و با تعریف شرایط مرزی مناسب، میدان جریان تراکم پذیر در ردیف پره تحلیل می شود. از معادلات ناویرٓ استوکس تراکم پذیر برای تحلیل میدان جریان، و برای مدل سازی آشفتگی از مدل k-e(R N G) استفاده می شود. از نتایج آزمون ردیف پره ی استاتور اولیه برای صحت سنجی نتایج حاصل از شبیه سازی استفاده می شود. بیشترین اختلاف نتایج حاصل از شبیه سازی با نتایج آزمون ردیف پره ی استاتور برابر 1٫14 درصد است. مقدار کاهش در تلفات فشار کل، برای ردیف پره ی روتور 1٫5 درصد و برای ردیف پره ی استاتور 3٫0 درصد در زاویه ی برخورد مورد نظر است، در حالی که مساحت استاتور بهبود یافته نسبت به پره ی اولیه 1٫3 درصد افزایش یافته است. این مقدار برای ردیف پره ی روتور بهبودیافته برابر2٫0 درصد است.
کلید واژگان: استاتور, روتور, بهینه سازی, تلفات فشار کلGas turbines have many applications in different industries. The axial turbine is one of the most challenging components of gas turbines for industrial and aerospace applications. With the ever-increasing requirement for high aerodynamic performance blades, two and three dimensional aerodynamic shape optimization is of great importance. In this paper, an automatic design procedure is presented for single point optimization of an axial flow turbine stator and rotor cascades. In this method, the genetic algorithm, the blade geometry generator, a computational mesh generator and the flow field solver are related. The objective function is the total pressure loss of the flow passing through the stator or rotor blade cascades. Particular modifications are performed with a limited number of optimization parameters, by changing stator and rotor blade thickness distribution. The stator and rotor airfoils are regenerated by adding a smooth perturbation of Wagner shape functions to the thickness distributions. Because of the symmetric geometry of the turbine blade cascade, periodic boundary conditions are used for simulations. Furthermore, three-dimensional and turbulent flow field investigations are numerically performed employing a compressible Navier-Stokes solver and the k-e (RNG) turbulence model. The experimental results of initial stator cascade are used for validation of numerical results. The experimental investigation is performed in the Gas Turbine Laboratory of Sharif University of Technology. The maximum deviation of numerical results from cascade test data is 1.14 percent. This optimization strategy resulted in a reduction of 1.5\% total pressure loss in the rotor and 3.0\% in the stator, for a prescribed incidence angle, while the cross sectional area of the modified stator and rotor blades increased, 1.3\% and 2.0\%, compared with the initial ones, respectively. It should be noted that for the rotor blade cascade, a multi-point optimization is required, based on a comparison of the original and modified loss-incidence angle chart results.Keywords: Stator, rotor, optimization, total pressure loss -
In this research, effects of excess air ratio and waste gate opening pressure threshold on NOx emission and performance in a turbocharged CNG SI engine are experimentally studied at 13-mode ECE-R49 test cycle. The engine power, boost ratio and charge air temperature are investigated experimentally at the cycle for different waste gate pressure thresholds. A code is developed in MATLAB environment for predicting engine performance and NOx and the results are validated with the research experiments. The effects of excess air ratio on the engine indicated power and specific fuel consumption as well as NOx emission are numerically investigated at WOT by the code. NOx emission of WOT is max at excess air ratio of 1.1. Simulation reveals that higher excess air ratio at a rate of 20% decreases maximum indicated power 9% and improves minimum ISFC 7%. Experiments indicate that brake power augments with increase of the pressure threshold especially at high loads and speeds due to higher boost ratio. It is also found that changing the threshold from 16 mmHg to 200 and 265mmHg decreases total bsNOx at rate of 6 and 12%, respectively. The threshold increase to 323mmHg augments total bsNOx. Therefore, the threshold of 265mmHg is optimum threshold among the four pressure thresholds experimented.Keywords: Turbocharged CNG SI Engine, NOx Emission, Performance, ECE, R49 Test Cycle, Excess Air Ratio, Waste Gated Turbocharger
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Natural gas is considered to be the most promising alternative fuel considering economy and clean burning. At the present, emission regulations for NG are restricted with Euro IV, V and even for Euro VI and these regulations are expected to become more restricted in future. Emission generation characteristics of pure natural gas is fairly known, however more experimental investigation of natural gas combustion is necessary. In this research, a turbocharged natural gas SI engine is investigated experimentally. Emission and performance characteristics of the engine at WOT and lean burn conditions are studied and validated experimentally and theoretically. A computer code is also developed in MATLAB environment for predicting engine performance and NO emissionsand the results are validated with experimental data. Thermal boundary layer, as a novel approach, is considered in the simulation and a better agreement of predicted mass fraction burned was achieved at end part of combustion process when compared with experimental results. Experimental results have revealed that turbocharger match at mid engine speed, waste-gate opening and increase of friction losses at high engine speed would decrease the torque and resulted in better torque back-up. Boost pressure, controlled by opening range of waste gate based on compressor outlet pressure, remained nearly constant at speeds higher than 1450 rpm. NOx emission reduced with engine speed increase due to shorter timethat burned gases remain at high temperatures, although they have higher temperature at high engine speeds.NO emission increased with the increase of excess air ratio until it reached to its peak value at about 1.1 from stoichiometric mixture and then decreased. NO emission decreased substantially with increase of spark timing retard. Brake specific UHC and CO2 emissions were min at mid speed range and WOT.Keywords: natural gas, turbocharged, turbulence, combustion simulation, thermal boundary layer, NOx, CO, UHC, CO2
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In this article, the effects of volute cross section shape and centroid profile of a radial flow compressor volute were investigated. The performance characteristics of a turbocharger compressor were obtained experimentally by measuring rotor speed and flow parameters at the inlet and outlet of the compressor. The three-dimensional flow field model of the compressor was obtained numerically solving Navier-Stokes equations with SST turbulence model. The compressor characteristic curves were plotted. For model verification, the results were compared with experimental data, showing good agreement.Modification of a volute was performed by introducing a shape factor for volute cross section geometry. By varying this parameter, new external volutes were generated and modeled while the original volute was intermediate volute. The effect of volute cross section shape on compressor pressure ratio and isentropic efficiency at design rotational speed were investigated.Also pressure non-uniformity around compressor impeller was investigated using pressure taps around the impeller outlet to verify numerical results. This effect was considered and reported for new cases using numerical results.The results show how the shape and centroid profile of volute circumferential cross sections can influence the compressor characteristics and circumferential static pressure non-uniformity.Keywords: Radial flow compressor, Turbocharger, Volute, Performance characteristic, Pressure non, uniformity
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روشی نوین در طراحی معکوس مبتنی بر گلوله- اسپاین برای مجاری متقارن محوری با کاربرد در توربین های گازیدر این تحقیق یک روش جدید برای طراحی معکوس مجاری تقارن محوری ارائه شده است. این روش که جزء روش های تکراری است، با یک حدس اولیه برای هندسه مجرا شروع شده و تا رسیدن به هندسه مطلوب، پس از هر مرحله حل عددی جریان، یک اصلاح شکل برای رسیدن به توزیع فشار مطلوب صورت می گیرد. تغییر شکل مجرا توسط یک الگوریتم جدید بنام گلوله-اسپاین انجام می شود که در این تحقیق معرفی و توسعه داده می شود. در این الگوریتم، دیواره مجرا با گلوله های فرضی جایگزین می شود که به صورت آزادانه می توانند در راستاهای مشخصی به نام اسپاین حرکت کنند. در هر مرحله تغییر شکل مجرا، معادلات اویلر روی صفحه تقارن محوری مجرا حل می شود. نرخ همگرائی بالا و امکان ترکیب آسان و سریع این الگوریتم با هر کد تحلیل جریان را می توان از مزایای اصلی این روش بیان کرد. با اصلاح توزیع فشار روی دیواره های داخلی و خارجی یک نازل حلقوی، به عنوان یک مورد عملی، از این روش برای اصلاح شکل هندسی آن استفاده می شود. با استفاده از این روش در نازل توربین گاز یک موتور جت، ضریب پیشرانش حدود 2 درصد و نیروی پیشرانش حدود 7 درصد بهبود یافته است.
کلید واژگان: طراحی معکوس, جریان داخلی, گلوله, اسپاین, معادلات اویلر تقارن محوری, نازل حلقویIn this study, a novel inverse design method is introduced for axisymmetric ducts in subsonic regimes. This method is an indirect one and starts with an initial guess. In this algorithm, the duct walls are simulated by hypothetical balls moving freely in specified directions, called spines. The advantages of this shape modification algorithm are high convergence rate and performing as a black box. Thus, the algorithm can easily be combined with any efficient flow solver. Based on this algorithm, the final nozzle propulsive force is increased about 7%.Keywords: Inverse Design, Internal Flow, Ball, Spine, Axisymmetric Euler Equations, Annular Nozzle -
In this investigation, the Flexible String Algorithm (FSA) used before for the inverse design of 2D subsonic ducts is developed and applied for the inverse design of subsonic and supersonic ducts with and without normal shock waves. In this method, the duct wall shape is changed under a novel algorithm based on the deformation of a virtual exible string in a ow. Deformation of the string due to the local ow conditions resulting from changes in the wall geometry is performed until the target shape satisfying the prescribed walls pressure distribution is achieved. The ow eld at each shape modi cation step is analyzed using an Euler equation solution by the AUSM method. Some validation test cases and design examples in subsonic and supersonic regimes are presented here, which show the robustness and exibility of the method in handling the complex geometries in various ow regimes. In the case of unsymmetrical ducts with two unknown walls, the FSA is modi ed to increase the convergence rate signi cantly. Also, the e ect of duct inlet and outlet boundary conditions on the convergence of the FSA is investigated. The FSA is a physical and quick converging approach and can eciently utilize ow analysis codes as a black box.
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Cavitating ow is investigated around marine propellers, experimentally and numerically. Two di erent types of conventional model propellers are used for the study. The rst one is a four bladed model propeller, so called model A, and the second one is a three bladed propeller, model B. Model A is tested in di erent cavitation regimes in a K23 cavitation tunnel. The results are presented in characteristic curves and related pictures. Finally, the results are discussed. Model B is investigated based on existing experimental results. In addition, model B is used for validation of the numerical solution prior to the testing of model A. The cavitation phenomenon is predicted numerically on a two dimensional hydrofoil, NACA0015, as well as propeller models A and B. The cavitation prediction on a hydrofoil is carried out in both steady and unsteady states. The results show good agreement in comparison with available experimental data. Propeller models are simulated according to cavitation tunnel conditions and comparisons are made with the experimental results, quantitatively and qualitatively. The results show good agreement with experimental data under both cavitating and noncavitating conditions. Furthermore, propeller cavitation breakdown is well reproduced in the proceeding. The overall results suggest that the present approach is a practicable tool for predicting probable cavitation on propellers during design processes. Keywords: Cavitation; Marine propeller; Cavitation tunnel; Experimental; CFD.
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In this paper, the performance of a turbocharger twin-entry radial in ow turbine is investigated analytically and experimentally under steady state, full and partial admission conditions. In this modeling, the mass ow rate, pressure ratio and eciency of the turbine are assumed unknown. The turbine geometry and the inlet total pressure and temperature are known, hence, the turbine performance characteristics can be obtained. In the turbocharger laboratory, performance characteristics of the turbine are determined, measuring the main parameters for various operating conditions. Comparing the model and experimental results shows good agreement. Also, considering the e ect of test parameters on performance uncertainty, it shows that the pressure ratio has more in uence. Finally, the uncertainty of eciency decreases as the pressure ratio increases.
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Iranian Journal of science and Technology (B: Engineering), Volume:32 Issue: 6, Dec 2008, PP 571 -584In this paper the performance characteristics of a turbocharger twin-entry radial inflow gas turbine with asymmetrical volute and rotor tip diameter of 73.6 mm in steady state and under full and partial admission conditions are investigated. The employed method is based on one dimensional performance prediction which is developed for partial admission conditions. Furthermore, this method is developed for the asymmetrical volute of the turbine considering the flow specifications. Experimental investigation of the research was carried out on special test facilities under full and partial admission conditions for a wide range of speeds. A comparison of experimental and modeling results shows good agreement. Interestingly, the turbine maximum efficiency occurs when the shroud side inlet mass flow is higher than that of the hub side.
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Performance prediction of twin-entry turbocharger turbinesIranian Journal of science and Technology (B: Engineering), Volume:29 Issue: 1, February 2005, PP 145 -155در اين مقاله، عملكرد توربينهاي دو ورودي جريان شعاعي تحت شرايط جريان دايم و ورودي نامساوي مدلسازي شده است. روشي كه طي اين تحقيق توسعه پيدا كرده و بر اساس روش يك بعدي پيش بيني عملكرد مي باشد. در مدلسازي يكبعدي، فرض مي شود كه خواص جريان در صفحه عمود بر جهت جريان يكسان باشد. چنين فرضي در تضاد با مشخصات جريان در ورودي روتوريك توربين دو ورودي با جريان ورودي نامساوي است. در اين مطالعه، به منظور تحليل رفتار توربين دو ورودي، روش مدلسازي يك بعدي در توربينهاي تك ورودي بهينه شده است…
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