Gas Turbine Engine Critical Component Risk Assessment Via Statistical Analysis

Author : Daniele Samuel Pascovici
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (757 download)

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Download or read book Thermo Economic and Risk Analysis for Advanced Long-range Aero Engines written by Daniele Samuel Pascovici and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: To conceive and assess engines with minimum global warming impact andlowest cost of ownership in a variety of emission legislation scenarios, emissions taxation policies, fiscal and Air Traffic Management environments aTechno economic and Environmental Risk Assessment (TERA) model isneeded. In the first part of this thesis an approach is presented to estimate the cost ofmaintenance and the direct operating costs of turbofan engines of equivalentthrust rating, both for long and short range applications. The three advancedtypes of turbofan engines analysed here are a direct drive three spool withultra high bypass ratio, a geared turbofan with the same fan as the direct driveengine and a turbofan with counter rotating fans. The baseline engines are athree spool for long range (Trent 772b) and a two spool (CFM56-7b) for shortrange applications. The comparison with baseline engines shows the gainsand losses of these novel cycle engines. The economic model is composed of three modules: a lifing module, aneconomic module and a risk module. The lifing module estimates the life of the high pressure turbine disk andblades through the analysis of creep and fatigue over a full working cycle ofthe engine. These two phenomena are usually the most limiting factors to thelife of the engine. The output of this module is the amount of hours that theengine can sustain before its first overhaul (called time between overhauls). The value of life calculated by the lifing is then taken as the baselinedistribution to calculate the life of other important modules of the engine usingthe Weibull approach. The Weibull formulation is applied to the life analysis ofdifferent parts of the engine in order to estimate the cost of maintenance, thedirect operating costs (DOC) and net present cost (NPC) of turbofan engines. The Weibull distribution is often used in the field of life data analysis due to itsflexibility?it can mimic the behavior of other statistical distributions such as the normal and the exponential. In the present work five Weibull distributionsare used for five important sources of interruption of the working life of theengine: Combustor, Life Limited Parts (LLP), High Pressure Compressor(HPC), General breakdowns and High Pressure Turbine (HPT). The Weibullanalysis done in this work shows the impact of the breakdown of differentparts of the engine on the NPC and DOC, the importance that each module ofthe engine has in its life, and how the application of the Weibull theory canhelp us in the risk assessment of future aero engines. Then the lower of the values of life of all the distributions is taken as timebetween overhaul (TBO), and used into the economic module calculations. The economic module uses the time between overhaul together with the costof labour and the cost of the engine (needed to determine the cost of spareparts) to estimate the cost of maintenance of the engine. The direct operatingcosts (DOC) of the engine are derived as a function of maintenance cost withthe cost of taxes on emissions and noise, the cost of fuel, the cost ofinsurance and the cost of interests paid on the total investment. The DOC ofthe aircraft include also the cost of cabin and flight crew and the cost oflanding, navigational and ground handling fees. With knowledge of the DOCthe net present cost (NPC) for both the engine and the aircraft can beestimated over an operational period of about 30 years. The risk model uses the Monte Carlo method with a Gaussian distribution tostudy the impact of the variations in some parameters on the NPC. Some ofthe parameters considered in the risk scenarios are fuel price, interestpercentage on total investment, inflation, downtime, maintenance labour costand factors used in the emission and noise taxes. The risk analyses theinfluence of these variables for ten thousands scenarios and then acumulative frequency curve is built by the model to understand the frequencyof the most probable scenarios. After the conclusion of the analysis of the VITAL engines as they werespecified by the Original Engine Manufacturer (OEM) (Roll? Royce, Snecmaand MTU), an optimisation work was done in order to try to improve the engines. The optimisation was done using two numerical gradient basedtechniques Firstly the Sequential Quadratic Programming? NLPQL andsecondly the Mixed Integer Optimization? MOST; the objectives of theoptimisation were two: minimum fuel burn and minimum direct operatingcosts. Because the engines were already optimized for minimum fuel burn, the optimization for minimum fuel burn didn?t show any meaningful results;instead the results for minimum DOC showed that the engines can have someimprovements. The ability of the three VITAL configurations to meet the future goals of theEuropean Union to reduce noise and gaseous emission has been assessedand has showed that the three engines cannot fully comply with futurelegislation beyond 2020. In the second part of this thesis three further advanced configurations havebeen studied to determine whether these are potential solutions to meet theACARE goals of 2020. For these more advanced aero engines only a performance and gaseousemissions analysis has been done, because it was no possible to do aneconomic analysis for the new components of these engines. Theseadvanced configurations feature components that have been studied only inlaboratories, like the heat exchangers for the ICR, the wave rotor and theconstant volume combustor, and for these it has not been done a lifinganalysis that is fundamental in order to understand the costs of maintenance, besides in order to do a proper direct operating costs analysis manyoperational flight hours are needed and none of these engine have reachedTRL of 7 and more which is the stage where flight hour tests are conducted. In this thesis a parametric study on three different novel cycles which could beapplied to aircraft propulsion is presented:1. Intercooled recuperative,2. wave rotor and3. Constant volume combustion cycle. These three cycles have been applied to a characteristic next generation longrange aero engine (geared turbofan) looking for a possible future evolutionand searching for benefits on specific thrust fuel consumption and emissions. The parametric study has been applied to Top of Climb conditions, the designpoint, at Mach number 0.82, ISA deviation of 10 degrees and an altitude of10686 m and at cruise condition, considering two possible designs:a) Design for constant specific thrust andb) Design for constant TET or the current technology levelBoth values correspond to the baseline engine. For the intercooled enginealso a weight and drag impact on fuel consumption has been done, in order tounderstand the impact of weight increase on the benefits of the configuration, considering different values of the effectiveness of the heat exchangers, thehigher the values the greater is the technical challenge of the engine. After studying the CVC and Wave rotor separately it has been decided to do aparametric study of an aero engine that comprises both configurations: theinternal combustion wave rotor (ICWR). The ICWR is a highly unsteadydevice, but offers significant advantages when combined with gas turbines. Since it is a constant volume combustion device there is a pressure raiseduring combustion, this will result in having lower SFC and higher thermalefficiency. It is an advanced and quite futuristic, with a technology readinesslevel (TRL) of 6 or higher only by 2025, so only a preliminary performancestudy is done, leaving to future studies the task of a more improved analysis.