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A near-field analysis is carried out to obtain the level of modulation interference due to rotating blades in a helicopter-borne pulse Doppler radar system. The interference power spectra are calculated for different values of antenna depression angle and helicopter (radar) speed at a constant helicopter altitude of 300 m. Numerical results for the case of 1 kW radiated power show that blade interference level is about 5 to 8 dBW/Hz less than that of the direct ground clutter in the clutter region. It extends, however, into the clutter-free region which may cause false alarms and degradation of the radar performance. 相似文献
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Radio interference generated in a helicopter-borne continuous wave (CW) Doppler radar system due to the rotating blades is analyzed. This problem has been previously treated for the case of pulse Doppler radar systems with very narrow (near zero) beamwidth. In this case the strong interference component returning directly from the blades (with no ground reflection) need not be considered as it reaches the receiver when it is still blinded. In the case of a CW Doppler radar, however, this interference component must be included. Numerical calculations show that the total blade interference power level, dominated by the direct component, is higher than that of the direct ground clutter in the radar clutter region. It decreases approximately as (f - fo)-4 in the radar clear region. It stays, however, well above the thermal noise level which might cause false alarm and degrade the radar performance. 相似文献
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将共轴对转螺旋桨气动噪声快速预测理论与气动载荷快速预测方法相结合,对共轴对转螺旋桨远场气动噪声进行预测。分析了BWI辐射效率对共轴对转螺旋桨BWI干扰噪声的主控影响。对从低至高的(单排6-12)前后等桨叶数对转桨进行了研究。结果表明虽然低桨叶数与高桨叶数对转桨的气动噪声特性不同,但是总体上前后指向性的高声压区仍然是由BWI噪声控制。同时等桨叶数的设计只是使高声压区更集中,却无法对其进行降低。随后,对比了不同桨叶数共轴对转螺旋桨远场气动噪声的表现,认为不等桨叶数对转桨气动噪声普遍优于等桨叶数情况。得出了总桨叶数相同情况下对转桨前后桨叶数的搭配方案。对近场噪声高精预测方法将在未来的研究中对辐射效率的具体机理进行研究。 相似文献
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复合材料在桨叶上广泛应用的同时使桨叶的受力、刚度特性比传统的桨叶更为复杂。为了降低桨叶工作时动应力和旋翼的振动水平,有必要对旋翼桨叶进行动力学特性分析。对旋翼总体参数及桨叶气动参数进行设计,采用CFD 方法对旋翼悬停状态进行气动特性分析,将桨叶三维非线性弹性模型分解为二维线性剖面模型和一维非线性梁模型进行动力学特性分析。结果表明:该旋翼能够成功拉起230 kg 级无人直升机,悬停效率大于0.65,工作转速下桨叶的固有频率与8 阶以下的气动激振力频率保持一定的范围,避开了转速共振区,满足桨叶动力学设计要求。 相似文献
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Field measurements of a modified Sikorsky S-55 helicopter target were carried out to investigate rotary-wing aircraft Doppler radar signature phenomenology. The results of the data analysis with regard to classification and identification of the aircraft based on its signature are presented. It was found that using the Doppler radar return and appropriate feature extraction techniques, the helicopter's design features can be estimated. Target backscatter from the main rotor blades, tail rotor blades, or hub can be used for target detection, acquisition, and classification as a rotary-wing aircraft. The extraction of configuration and blade count features can further define the helicopter for identification 相似文献
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If modern airborne radar systems are to function properly, the radar antenna radiation patterns must meet certain specifications. Until recently, most radar antennas were designed and tested in a clean antenna environment, i.e., there is no near field scattering from host structures or radome effects. However, these higher order effects are the matter of increasing concern with added performance demands in the ever-increasing jammer and clutter interference environments. We investigated the capabilities and limitations of currently available analysis techniques and computer codes for installed performance of airborne radar antenna systems. Then we developed an extended ray-optical technique that could predict total installed performance of airborne radar antenna systems, i.e., the near field scattering from aircraft structures and radome effects. The new analysis technique utilized a ray-tracing method in both airframe and radome simulation. Thus, it can efficiently predict the total installed performance of large radar antenna systems on an aircraft structure 相似文献
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透平叶片疲劳强度可靠性设计的研究 总被引:3,自引:1,他引:3
本文提出了透平叶片疲劳强度的可靠性设计方法。该方法把透平叶片的静应力、动应力和叶片疲劳强度处理为随机变量,使用疲劳应力分布和疲劳强度分布的干涉模型,在设计阶段确定透平叶片的可靠度。文中给出了透平叶片可靠性设计的实例。 相似文献
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透平叶顶泄漏能量损失的数值计算 总被引:1,自引:1,他引:1
商用N S求解器已经被用于透平动叶顶部空隙的非定常流场的模拟和研究。本文介绍了一种新的用于透平动叶片顶部空隙区域流场计算的能量损失方法 ,可以方便地用于各种流场。发现高黏度效应区域位于上端壁附近而不是在叶片顶部。研究表明对于不同的动叶片其顶部泄流的能量时均损失是不一样的。该结果提供了一个有用的线索 ,可以通过叶片设计者设计出不同几何和空气动力学参数的非统一的动叶片 ,从而减小能量损失 相似文献
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对带有周向前弯和周向后弯叶片的低压轴流风机,采用PIV技术测量小流量工况下叶顶区域瞬态速度场。基于小流量压力峰值工况下的瞬态测量结果,详细阐述了周向弯曲叶片叶顶泄漏涡的演化过程。结果表明:小流量压力峰值工况下,周向弯曲叶片叶顶泄漏涡存在瞬态特性,泄漏涡起源向前缘方向迁移,涡核在向下游发展的过程中不断破碎,沿端壁向通道中部迁移,并发生径向迁移;周向后弯叶片的泄漏涡较周向前弯叶片迁移明显,涡核破碎过程剧烈;周向前弯叶片有利于叶顶泄漏涡的控制。 相似文献
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《IEEE transactions on aerospace and electronic systems》1990,26(5):792-803
Signal or target detection is sometimes complicated by the presence of strong interference. When this interference occurs mainly in the sidelobes of the antenna pattern, a solution to this problem is realized through a sidelobe canceler (SLC) implementation. Since the false-alarm probability is a system parameter of special importance in radar, an interference-canceling technique for radar application should maintain the false-alarm probability constant over a wide range of incident interference power. With the requirements of sidelobe interference cancellation and constant false alarm rate (CFAR), a new algorithm for radar detection in the presence of sidelobe interference is developed from the generalized likelihood ratio test of Neyman-Pearson. In this development, the received interference is modeled as a nonstationary but slowly varying Gaussian random process. Cancellation of the sidelobe interference is based upon a `synchronous' estimate of the spatial covariance of the interference for the range gate being tested. This algorithm provides a fixed false-alarm rate and a fixed threshold which depend only upon the parameters of the algorithm 相似文献
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Waters William M. Eikenberg Andrew F. 《IEEE transactions on aerospace and electronic systems》1968,(6):886-892
This paper describes the design, construction, and performance of an experimental radar, in which an electronically scanned X-band array is employed as the receiving antenna. Backscatter from targets uniformly illuminated from a separate transmitting antenna is intercepted by 128 horn antennas, unequally spaced over a nine-foot circular aperture. The received signals are processed electronically to provide a complete scan of a 30X30 degree field every ten milliseconds. Resulting target images were displayed on a cathode ray tube and recorded on 16-mm motion picture film, for varying conditions of target motion using monochromatic and frequency-modulated X-band illumination. Sequences of motion picture frames obtained from a rotating copper cone are presented, which demonstrate significant changes in the image and side-lobe interference patterns for small changes in target aspect angle. Side-lobe interference effects were reduced by integrating many antenna scans as the target rotated; a clear image of a foil letter R is presented that demonstrated this result. The main objective of this work was to test this radar technique as an approach to target recognition. 相似文献
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对带有周向前弯和周向后弯叶片的低压轴流风机,采用双丝热线技术实验研究了周向弯曲叶片出口三维流动随流量降低变化规律。基于测量结果,详细阐述了周向弯曲叶片流道内三维流动结构的演化发展过程,分析非设计工况下叶片弯掠对流动的影响规律,结合径向平衡方程讨论了周向弯曲叶片对变工况边界层迁移的控制。结果表明:小流量工况下,周向弯曲叶片显著改变了流道内流动结构,且明显改善上下端壁区域的流通性,对于扩大稳定工作范围有着积极的作用;由于旋转离心力的增大,Fr对于径向压力梯度影响也发生变化,从而改变边界层的迁移方向和速度。 相似文献
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微小整体叶轮作为微型发动机的重要组成部分,其加工质量直接影响微型发动机的使用性能。针对微小整体式复杂叶轮流道狭窄、叶片扭曲大和长厚比大等特点,开展了微小复杂扭曲整体式叶轮五轴联动微细铣削加工方法研究。针对微小叶轮加工过程极易发生变形、过切和碰撞干涉等问题,对微小叶轮的加工过程进行工艺规划,建立了微小叶轮流道加工刀具选择的约束方程,计算出叶轮加工刀具的最大理论直径。通过CAM软件对叶轮进行切削仿真,验证了刀具选择和工艺规划的正确性。通过五轴联动微细铣削试验,得到了具有6个直径10mm的叶片、叶片最小厚度0.15mm、叶片最小相邻间距0.58mm的7075铝合金微小整体叶轮。 相似文献
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