Study on the influence of blade on electromagnetic scattering characteristics in the open-ended cavity

https://doi.org/10.1016/j.jocs.2022.101716Get rights and content

Highlights

  • The mean RCS of the open-ended cavity decreases with the increase of the blade number while the incident angle is in the -10° ~10° range, and reaches the minimum for the number of blades equals to 11.

  • The mean RCS of the cavity increases with the increase of the blade stages, and the mean for the incident angle -10° ~10°range is larger than the -30°-30° range.

  • The mean RCS of the cavity first decreases and then increases with the increases of the angle between the blades of the two stages, and reaches to the minimum while the angle of the blade is 6° and 9° for the horizontal polarization and the vertical polarization, respectively.

Abstract

The aero engine intake is the most important and strongest scattering source of the combat aircraft in the forward area. The incident electromagnetic wave will directly illuminate the fan/compressor blades which would change the forward radar cross section (RCS) distribution of the intake. The influence of the internal blade geometry parameter, including blade number, blade stages and the angle between two-stage blades on the RCS of the open-ended cavity was obtained by using the method of moment with the multi-layer fast multipole. The results show that the mean RCS of the cavity decreases with the increasing blade number in the smaller detection angle range. The mean RCS of the cavity increases with the increasing blade stage which changes the transmission path of the incident electromagnetic wave inside the cavity. And compared with the cavity with only one blade, the mean RCS with three-stage blades increases by more than 55%. With the angle between the two-stage blades increasing, the mean RCS of the cavity decreases first and then increases.

Introduction

The aircraft engine intake is a typically electrically large size cavity in computational electromagnetism and one of the main sources of electromagnetic scattering in the forward motion of the aircraft. The existing research shows that the single-engine aircraft inlet would contribute 40% of the radar scattering in the forward area. While the ratio of double-engine aircraft can reach 60% or higher. Therefore, whether the radar scattering of the intake can be effectively controlled is directly related to the RCS level of the whole flight in the forward motion. It is a guarantee to achieve omnidirectional stealth that analyzing and studying the electromagnetic scattering characteristics of the intake [1], [2], [3], [4].

At present, more researchers are focused on electromagnetic scattering characteristics of the open-end cavity such as the intake and nozzle of the aeroengine. Paknys R and others [5] have carried out numerical calculation and experiment test on the electromagnetic scattering characteristics of an electrically large size rectangular cavity. It’s been verified that the calculation accuracy of adaptive ray method and modal ray method in cavity calculation. Chan K K and others [6] have developed an auxiliary program based on the modal method to predict the scattering of electrically large and complex jet inlets and engines. Also the monostatic RCS measurements and the numerical simulation were carried out at X-band on a 0.706 m diameter test cylinder containing 30 skewed blades mounted on a center shaft with a conical hub. The results show that the numerical method had higher simulation accuracy compared with the experiment results. P.M.David and others [7] have carried out numerical simulation and experimental tests on the RCS of a simple cavity under different configurations which was considered that the influence of straight or curved blades, different fixed blades position, and free motion capability at adjustable speed. The result shows that the shape and position of the blade have obvious effect on the RCS of the cavity and the measurement dates could be used to analyze the response of cavities as well as radar cross section reference data for validating existing and future prediction codes. Vogel M [8] has presented an efficient three-step method to compute the RCS of an aircraft with engine inlets that include fan blades. The results shows that the method combines rigorous and asymptotic in a way that reduces total simulation time relative to other hybrid methods. A.Sabihi [9] studied the RCS of a cavity covered by a metallic grid net. The radar ray incident on a grid net installed on a cavity may create six types of propagation. It had been compared that the effects of three out of six properties to a cavity without grid net. This comparison shows that RCS prediction of cavity having a grid net is much more reduced than that of without one. Liu J and others [10] had extended the finite element-boundary integral(FE-BI) method to calculate the RCS of engine inlets with complex internal structures. The results obtained with relatively little memory and computational cost agree very well with the measured data for a curved cavity and an inlet terminated with an array of straight blades. Li Yuefeng and others [11] studied the influence of inlet shape on the electromagnetic characteristics of S-shaped inlet port. The RCS of the S-shaped inlet with five import shapes such as round, oval, rectangle, diamond, W shape,was calculated by iterative physical optics method.The results show that the inlet with W inlet shape can effectively reduce the RCS value of the S-shaped inlet. Deng Xuejiao and others [12] analyzed the influence of lip chamfering modification on the electromagnetic scattering characteristics of the S-shaped inlet with diamond import shape. The results show that the lip chamfering modification was an effective RCS reduction measure during the small detection angle range which could reduce the RCS of the edge diffraction field. Zhang Le and others [13] have studied the influence of three different shapes of conformality-design inlets on the electromagnetic scattering characteristics and aerodynamic characteristics of the double S-shaped inlet. The results show that the rectangular inlet has the best internal flow characteristics. Because the three inlet shapes have similar RCS mean distribution at 0° angle of attack; When the inlet terminal is open, the rectangular inlet model has the best stealth performance. Hang Haoran and others [14] studied the influence of bending distance of S-shaped inlet on the aerodynamic and electromagnetic scattering characteristics. Increasing the bend distance could effectively reduce the RCS, while reducing the total pressure recovery coefficient. The mechanism of this phenomenon was analyzed which has guiding significance for the integrated design of stealth aerodynamics of the inlet. Gao Xiang and others [15] studied the numerical calculation and analysis of the aerodynamic performance and radar scattering characteristics of four different inlets, which were elliptical, trapezoidal, D-shaped and rectangular double S-curved inlets. The results indicated that the elliptical inlet enjoys better aerodynamic performance, while the trapezoidal inlet has lower yaw detection surface RCS. Compared with the elliptical inlet, the maximum RCS can be reduced by 2.54 dBsm when the circumferential comprehensive distortion is less than 0.29%.

Above studies mainly centered on the influence of the main geometric characteristic parameters of the inlet on its own RCS distribution law. Instead, the influence on the internal structure of the inlet, especially the fan or compressor blade, on the electromagnetic scattering of the inlet have not been taken into account. Alongside that, Zhang Le and others [16] studied the effect of grille of different size on the electromagnetic scattering features of straight cavity inlet via experimental test and numerical simulation. In accordance with the results, under the typical incident frequency of X band, the efficiency of grid electromagnetic shielding is about 43% when the spacing of grille holes is λ/2. As such, the increase of grid thickness enables to increase the efficiency of grid electromagnetic shielding, but the amplitude of increase is relatively small.

To sum up, the research on the electromagnetic scattering characteristics of the inlet mainly focuses on the influence of the inlet lip shape and the RCS reduction method, while the study on the RCS is inefficient for the existence of the inner blade structure and the change of geometric parameters of the inlet cavity. Therefore, it has been carried out the research on the influences of the number of blades in the cavity, the number of blades and the angle of the stroke after the blade rotation on the electromagnetic scattering of the cavity.

Section snippets

Principle

Numerical simulation methods for EM scattering of cavities with multiple scales and complicity can be divided into two categories: for one thing, the methods of high frequency approximation, such as ray tracing method, iterative physical optics, optics and so forth; for another thing, the full-wave numerical method mainly refers to method of moments, finite element method and finite time domain method. As such, due to the fact that the blade size of the cavity is smaller than the geometric

Presentation of results

Fig. 6 shows the incident angle setting. The incident angle (θ) ranges from − 30–30°, and the angle interval is 1°. The calculate frequency is 10 GHz. The wall grid division scale is λ/8 according to the calculation requirement of MoM.

Conclusions

The method of moment combined with the multi-layer fast multipole method is used to study the effects of the number of blades, the number of stages and the angle between the two stages on the RCS of the cylindrical cavity with a boss.

  • (1)

    The mean RCS of the open-ended cavity first fluctuates and then decreases with the increasing blade number within the incident angle range of − 10° ~10°. When the number of blades in the cavity is 11, the mean RCS of the cavity is the smallest.

  • (2)

    The mean RCS of the

CRediT authorship contribution statement

Guo Xiao: Conceptualization, Methodology, Data curation, Writing – original draft preparation. Wen Zhenhua: Writing – review & editing. Li Shuhao: Data Visualization. Yang Qingzhen: Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This study was co-supported by the National Natural Science Foundation of China (51975539, 72001192), the Natural Science Foundation of Henan Province (202300410490), the Science and Technology R&D Program of Henan Province of China (202102210237, 222102210050), the Youth Talent Support Project of Henan Province (2021HYTP017) and the Aeronautical Science Foundation of China (2018ZD55008). The authors also wish to thank them for their financial support.

Guo Xiao, male, born in 1988, Lecture, Ph.D., main research direction is calculation and analysis of target characteristics of aerospace engine inlet / exhaust system.

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Guo Xiao, male, born in 1988, Lecture, Ph.D., main research direction is calculation and analysis of target characteristics of aerospace engine inlet / exhaust system.

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