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Numerical optimization of transonic natural laminar flow nacelles

Chinese Journal of Aeronautics 2023年第6期36卷 35-51页

作者： Chongyang YAN Yufei ZHANG Meihong ZHANG School of Aerospace Engineering Tsinghua UniversityBeijing 100084China Shanghai Aircraft Design and Research Institute Shanghai 201210China

natural laminar flow nacelle is a promising technology for drag reduction.In this paper,an optimization platform is established for the design of transonic axisymmetric and threedimensional natural laminar flow nacelles for large civil aircraft.The platform adopts the class/shape transformation method for geometric parameterization,a four-equation transition model for transition prediction,and the differential evolution algorithm combined with the radial basis function surrogate model as the optimization algorithm.The optimized axisymmetric nacelle demonstrates approximately 31%chord length of laminar flow,with the drag reduction of 13.3%.The influence of the Reynolds number and inlet mass flow rate on the optimization result is also investigated.The axis-symmetric nacelle optimization method is further used for the section profile design of a non-axisymmetric nacelle.An equivalent method is used to simulate the different local flow angles at different sections in the circumferential direction of the non-axisymmetric nacelle by using different inlet mass flow rates of the axisymmetric nacelle.The optimized natural laminar flow nacelle maintains over 30%chord length of laminar flow with robustness to the change of the freestream angle of attack.The total drag of the non-axisymmetric nacelle is reduced by 5.4%under cruise conditions.

关键词： Aerodynamic design Nacelle natural laminar flow Optimization Transonic

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Double-decoupled inverse design of natural laminar flow nacelle under transonic conditions

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Chinese Journal of Aeronautics 2023年第6期36卷 1-18页

作者： Heng ZHANG Jie LI Zhao YANG School of Aerospace Engineering Tsinghua UniversityBeijing 100084China School of Aeronautics Northwestern Polytechnical UniversityXi’an 710072China

The inverse design based on the pressure distribution is an essential approach to realize the improvement of natural laminar flow(NLF) performance for nacelles. However, the direct definition of target pressure distribution at design point is challenging for the dilemma to consider the constraints of shock wave and laminar flow at the same time. In addition, the universality of method will be limited when the inverse design is strongly coupled with the solver. Thus, a double-decoupled methodology based on the relationship of pressure distributions between design and off-design points is proposed in this paper, which realizes the decoupling of constraints in shock wave and laminar flow on target pressure distribution as well as the decoupling of flow field solution and inverse design method. Aimed at an isolated flow-through-nacelle of high bypass ratio, the target pressure distribution with appropriate favorable gradient and shock-free feature is defined according to physical principles at the off-design point of Ma = 0.80 while the transonic and laminar performance are examined at the design point of Ma = 0.85. The solution of flow field is based on γ-Re_(θ) transition model and the inverse design is based on residual-correction method. With the inverse design starting from off-design point, the performance of shock wave and laminar flow at design point are both improved. The local shock wave after the lip of nacelle is eliminated effectively while the streamwise length of laminar flow region is doubled and exceeds to 30% of the chord length. The percentage of drag reduction for outboard surface is 12.7% for friction drag, 7.8%for pressure drag and 10.5% for total drag. The effects of inverse design on the process of transition are analyzed with detailed flow features. The robustness of laminar flow is examined under different variation factors of freestream which are deviated from the design point.

关键词： Drag reduction Inverse design method Nacelle natural laminar flow Transonic

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维普期刊数据库

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Transition prediction and sensitivity analysis for a natural laminar flow wing glove flight experiment

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Chinese Journal of Aeronautics 2021年第8期34卷 34-47页

作者： Tihao YANG Hai ZHONG Yifu CHEN Yayun SHI Junqiang BAI Feifei QIN Northwestern Polytechnical University Xi'an 710072China Chinese Flight Test Establishment Xi'an 710089China Xi’an Jiaotong University Xi'an 710049China ETH Zürich(Swiss Federal Institute of Technology in Zurich) Zurich 8093Switzerland

natural laminar flow technology can significantly reduce aircraft aerodynamic drag and has excellent technical appeal for transport aircraft development with high aerodynamic efficiency.Accurately and efficiently predicting the laminar-to-turbulent transition and revealing the maintenance mechanism of laminar flow in a transport aircraft’s flight environment are significant for developing natural laminar flow wings.In this research,we carry out natural laminar flow flight experiments with different Reynolds numbers and angles of attack.The critical N-factor is calibrated as 9.0 using flight experimental data and linear stability theory from a statistical perspective,which makes sure that the relative error of transition location is within 5%.We then implement a simplified e^(N) transition prediction method with a similar accuracy compared with linear stability theory.We compute the sensitivity information for the simplified eN method with an adjointbased method,using the automatic differentiation technique(ADjoint).The impact of Reynolds numbers and pressure distributions on TS waves is analyzed using the sensitivity information.Through the sensitivity analysis,we find that:favorable pressure gradients not only suppress the development of TS waves but also decrease their sensitivity to Reynolds numbers;there exist three special regions which are very sensitive to the pressure distribution,and the sensitivity decreases as the local favorable pressure gradient increases.The proposed sensitivity analysis method enables robust natural laminar flow wings design.

关键词： e^(N)method Flight experiment natural laminar flow Sensitivity analysis Transition prediction

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