Mathematical Problems in Engineering

Volume 2019, Article ID 5176560, 11 pages

https://doi.org/10.1155/2019/5176560

## Impact of Modeling Simplifications on Lightning Strike Simulation for Aeroengine

Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

Correspondence should be addressed to Zhi-feng Ye; nc.ude.aaun@fzy

Received 3 July 2019; Accepted 19 September 2019; Published 10 October 2019

Academic Editor: Rafał Stanisławski

Copyright © 2019 Yi-fan Qian et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

With the development of electromagnetic simulation software and affordable hardware, it is allowed for us to complete simulations for EMC purposes. However, simulation demands will be immense when simulations for models with complex structures, especially aircraft components, have to be solved. Hence, it is meaningful to investigate how to minimize the computational demands. One of the solutions to reduce the simulation expense is the simplification for the simulated model. But the simplified model should be guaranteed to provide credible simulation results which do not deviate from the original model apparently. Generally, the difference between the simulation results and experimental data is estimated, or if the experimental conditions are not achieved, the comparison between the simplified model and the original one has to be analyzed, at least. This paper explores the electromagnetic simulation of a turbofan engine encountering lightning strike. With the simplifications of different components on the turbofan engine, the influences on induced currents of engine controller cables are simulated and analyzed based on the transmission-line matrix method. A combining method of components removal and geometric structure simplification is proposed to simplify the whole engine model. Simplified components include compressor, combustion chamber, turbine, and nozzle. The effects of different simplification methods are quantified, and the rationality of the simplified model is verified by simulation analysis.

#### 1. Introduction

A commercial aircraft suffers lightning strike once a year on average in the world. The lightning impact can be divided into two categories: direct and indirect. Direct impact causes physical damage to the structure due to the direct contact of lightning. Indirect effects mainly refer to the transient changes of induced currents in cables of aircraft caused by electromagnetic effect of lightning strikes. These transient changes are caused by electromagnetic fields generated by lightning currents, which diffuse along the surface of aircraft through components such as windows or composites. In the interior of aircraft, these transients can exceed the immunity limit of the equipment, cause malfunction or damage, and endanger flight safety [1]. In order to solve the problem of lightning protection, electromagnetic simulation technology is increasingly applied to aircraft designs. Considering the lightning protection problem in the development stage of aircraft, it can reduce the cost of development and shorten the development cycle. Therefore, relevant research institutions have devoted large amount of manpower and material resources in the electromagnetic simulation technology of aircraft [2].

Aeroengine is the most significant part of aircraft. Once struck by lightning, if the shielding protection is weak, it will cause a devastating impact. In recent years, in order to investigate the electromagnetic protection problems often encountered by aeroengines in flight, various algorithms have been applied to such large-scale simulation. Da Silva and Bastos used the finite element method (FEM) to simulate and analyze large-scale electronic devices and simplified the simulation model [3]. Guiffaut and Reineix applied the finite-difference time domain method (FDTD) in the simulation of electromagnetic compatibility (EMC) for a small aircraft, and they analyzed the distribution of electromagnetic field for the aircraft under high-intensity radiation [4]. High-precision simulation can provide guidance for the design, certification, and life cycle prediction of aeroengine, thus improving flight safety. At the same time, with the increasing computing power of calculating machine, it is possible to simulate the electromagnetic effect for the whole aeroengine structure. However, the electromagnetic simulation of such large complex structures is a time-consuming process, and the calculation process is arduous. For the lightning strike simulation of aeroengine, the calculation time of the simulation can be even up to several weeks. It is definitely meaningful to reduce the cost of such simulations so that the development cycle can be shortened [5]. Recently, the development of electromagnetic simulation software and affordable hardware allows scholars to complete simulations for large-scale structures. But electromagnetic simulation demands are still enormous for a model with complex structures, especially aeroengine. Hence the need to minimize the computational demands is worthy of investigation. One of the feasible methods to reduce the computational expense is the simplification for the original model. But the simplified model should be guaranteed to provide credible results of simulation. Generally, the comparison of the simulation results with experimental data is estimated. Actually, if there are no experimental data, it is necessary to analyze the difference of simulations between the simplified model and the original one. Therefore, a simplification method is urgently needed to reduce the overall cost and the required time of simulation. In the past 10 years, a few scholars began to discuss the simplification methods of such kinds of simulation, gradually. The existing simplification methods mainly focus on the details and parts of the electromagnetic simulation model. Arnaud Christophe of Fiat Automobile Companys in Brazil has roughly classified the structural components of an automobile model, the components were removed and simulated one by one, and comparison between the effects of different simplified classifications on the electromagnetic field intensity in the vehicle was obtained [6], but the model is simple so the revivification is low. Reznicek and Raida of EVEKTOR Aircraft Manufacturing Company in Czech simulated the electromagnetic field of its small-sized turboprop aircraft, taking the electromagnetic field intensity in the cabin as the simulation target, some parts of the aircraft were removed and simplified. The simulation results after removal and simplification were compared, and the rationality of geometric simplification in electromagnetic simulation was verified [7]. However, effects of induced currents in cables caused by lightning strike were not studied. Engineer Guadalupe Gutierrez et al. of Airbus simplified the three components in the structure of a turboprop loaded by A400M transporter, i.e., the air particulate separator, the oil cooler, and the electric contact. The effects of simplification on the induced currents in the internal cables of turboprop were studied in detail to prove the rationality of simplification [8]. The peak values of the induced currents were taken as the judgment in this paper with the overall error of currents.

This paper is organized as follows. Section 2 provides the simplification method of aeroengine, Section 3 shows the modeling process of aeroengines and cables, simulation configurations are presented in Section 4, and comparison and analysis are shown in Section 5. Finally, simulation scheme and verification are presented in Section 6. In Section 7, we draw the conclusions briefly.

#### 2. Simplification Method

The primary task of geometric simplification is to define the simulation target. For an aeroengine, the largest impact of indirect lightning strike effect is that the transient current in the cable exceeds the immunity of the aeroengine controller, which leads to the malfunction and causes potential safety hazards. Secondly, the establishment of simulation model is also very significant. The higher the accuracy of structure and cable layout, the higher the simulation revivification, and the more complex the model details are, thus, more detailed grouping and simplification of components can be carried out. Although simplification is an important way to reduce simulation cost, the rationality of simplification is also needed to be guaranteed. Each simplified simulation should be compared with the simulation results of the original model, and the data should be analyzed in detail. The simplification methods of components are classified (removal, detail processing, and cannot be removed), so as to guarantee the rationality for simplification. For the electromagnetic simulation of a whole aeroengine structure, whether the model is simplified reasonably or not will greatly affect the accuracy of the final results, otherwise the simulation will be meaningless. The flow chart is shown in Figure 1.