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1.
A systematic analysis has been performed for many-years experimental data obtained in the wind tunnel T-203 (SibNIA) for testing
the models of passenger and transport aircraft for the case of harmonic oscillation at the pitch angle for low subsonic velocities.
The key features of behavior of aerodynamic derivatives coefficients and dependencies of current values of normal force coefficient
and longitudinal moment coefficient on the angle of attack have been demonstrated for the stalling modes of streamlining.
It was demonstrated that at near-critical angles of attack, we have a strong dependency of aerodynamic derivatives of pitch
moment on the normalized oscillation frequency for the range of natural values; this makes the traditional mathematical model
of aerodynamic loads (uses the aerodynamic derivatives at fixed frequencies of oscillation) unfit for the considered scope
of experimental tasks. 相似文献
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针对面对称高速飞行器滚转-偏航通道间存在的运动耦合、典型气动耦合和控制耦合,建立了耦合动力学模型,推导了耦合模态的数学描述;提出了基于滚转偏航/稳定比和副翼滚转/偏航操纵比的耦合模态分析方法,分析了副翼操纵对偏航通道的耦合影响程度;针对控制耦合引起的非最小相位特性,提出了基于偏航稳定力矩导数、副翼-偏航耦合力矩导数以及方向舵产生偏航力矩导数的控制耦合偏离边界条件,根据偏航稳定力矩导数、副翼-偏航耦合力矩导数的相对位置关系,确定控制耦合偏离区域,并分析了副翼控制滚转时的耦合失控特性.最后对失控特性进行了仿真验证,结果表明了耦合特性分析方法的有效性. 相似文献
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Yu. A. Mokin 《Thermophysics and Aeromechanics》2009,16(1):37-42
The influence of small attack and sweep angles on the rolling moment variation at a supersonic flow around the bodies close
to the bodies of revolution is considered. Based on the method of the differential hypothesis of locality the integral expressions
are obtained for the derivatives of the rolling moment coefficient with respect to the attack and sweep angles. The norm of
these derivatives is defined and the estimates for the norm are obtained. 相似文献
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Noise and vibration is a serious problem in all types of aircraft. Any techniques that lower cabin noise and vibration levels by even a few decibels with little or no weight or performance penalties are worth pursuing. Propeller synchrophasing is one such technique that has shown potential in aircraft with two or more propellers; however this technique is not being used to its full potential because the synchrophase angles are typically fixed. This paper provides a detailed examination of how the optimum synchrophase angles in a typical four-engine propeller aircraft vary with different altitudes and airspeeds, and how this information could lead to the design of new adaptive propeller synchrophasing systems and potentially yield improvements to other active noise control measures in propeller aircraft. 相似文献
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大飞机具有轻质大柔性特点,使得气动/结构耦合作用增强,在设计过程中需要考虑这种耦合效应,直接调用CSD/CFD方法计算周期长,无法满足工程需要.代理模型方法由于能显著提高工程优化设计的效率,已广泛应用于飞行器气动外形优化设计中.采用Kriging方法建立代理模型,通过求解EI函数最大值得到需添加的样本点以更新代理模型,提高代理模型的拟合精度,结合改进的粒子群最优化方法对大飞机的结构刚度进行了优化设计.结果表明,该优化方法能够处理复杂目标的全局优化问题,在保证升力系数及纵向稳定性能不恶化的前提下,降低飞机巡航状态的飞行阻力. 相似文献
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We investigate the effect of helix angles on polaron motion in poly-DNA in the framework of a tight binding model. A DNA molecule is supposed to have a uniform or a random distribution of the helix angles. It is found that a polaron moves faster along a DNA molecule with an overwinding helix than that with an unwinding one. In DNA molecule with randomly distributed helix angles, charge transport is suggested to be field-facilitated tunneling between spatial disordered potential wells. 相似文献
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采用气动力/热/结构耦合的方法对高速细长体飞行器结构热静气动弹性问题进行了研究.为保证耦合计算精度,达到准确预测热气动弹性特性的能力,气动力和气动热计算采用CFD数值模拟方法,热应力和热变形计算采用有限元方法并通过热考核试验验证.以该简单细长体飞行器模型为研究对象,对其热静气动弹性特性进行了计算与分析,计算结果表明:CFD/CSD耦合可准确模拟热气弹问题,且气动加热造成结构温升不均衡是结构变形的主导因素,力热耦合静气弹变形与单纯受力分析变形形式不同,对飞行器气动特性影响规律不同.准确预测飞行器热气动弹性特性对飞行器结构设计十分必要. 相似文献
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Ling-Fong Li 《Physics letters. [Part B]》1979,84(4):461-464
It is pointed out that Fritzsch's derivation of the mixing angles for a six-quark theory based on a SU(2)L × SU(2)R × U(1) model is in error. The correct formula for the mixing angles differs significantly from Fritzsch's results. 相似文献
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大攻角气动特性预测与气动建模是新型飞行器提升飞行性能的重要内容.以轴对称导弹简化模型为研究对象,首先采用计算流体力学方法,对70°大攻角状态的非定常气动特性进行数值模拟,计算方法基于RANS的N-S方程,湍流模型采用SA模型,对流场采用有限体积法离散,无黏项采用Roe通量差分分裂格式,黏性项采用中心差分,时间推进采用LU-SGS格式的双时间步法.飞行器运动模式采用强迫振荡的方式,对5种不同振荡频率进行了非定常数值计算,并记录每一内迭代周期最终的气动力和力矩数值.其次,以CFD预测结果作为气动建模的样本,采用动导数模型、多项式模型等传统方法,进行气动建模,并分析其有效性和精度.最后采用神经网络方法对大攻角非定常气动力进行建模,并和动导数模型、多项式模型进行精度对比.结果表明,基于神经网络的人工智能气动建模方法具有较高的精度和适应性.该方法为飞行器大攻角非定常非线性气动建模,大攻角飞行稳定性分析与控制提供理论参考. 相似文献
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Estimation of energetic efficiency of heat supply in front of the aircraft at supersonic accelerated flight. Part 1. Mathematical models 总被引:1,自引:1,他引:0
A. F. Latypov 《Thermophysics and Aeromechanics》2008,15(4):537-548
Fuel economy at boost trajectory of the aerospace plane was estimated during energy supply to the free stream. Initial and
final flight velocities were specified. The model of a gliding flight above cold air in an infinite isobaric thermal wake
was used. The fuel consumption rates were compared at optimal trajectory. The calculations were carried out using a combined
power plant consisting of ramjet and liquid-propellant engine. An exergy model was built in the first part of the paper to
estimate the ramjet thrust and specific impulse. A quadratic dependence on aerodynamic lift was used to estimate the aerodynamic
drag of aircraft. The energy for flow heating was obtained at the expense of an equivalent reduction of the exergy of combustion
products. The dependencies were obtained for increasing the range coefficient of cruise flight for different Mach numbers.
The second part of the paper presents a mathematical model for the boost interval of the aircraft flight trajectory and the
computational results for the reduction of fuel consumption at the boost trajectory for a given value of the energy supplied
in front of the aircraft. 相似文献
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利用改进的Ginder-Epstein模型计算了翠绿亚胺聚合物在参数V4,0取值于1.8~35.8 eV的自洽变分基态,并通过芳环扭角的变化来估算聚合物压强,给出了V4,0,芳环扭角及能隙与理论压强之间的最小二乘拟合.结果表明随此参数的增大,芳环扭角和能隙都缩减而理论压强升高.当理论压强由零压增至3.0 GPa左右时,能隙先快后慢从2.0 eV减小至最小值0.87 eV.这理论与该聚合物的高压电导测试结果一致. 相似文献
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利用改进的Ginder-Epstein模型计算了翠绿亚胺聚合物在参数V4,0取值于1.8—35.8 eV的自洽变分基态,并通过芳环扭角的变化来估算聚合物压强,给出了V4,0,芳环扭角及能隙与理论压强之间的最小二乘拟合。结果表明随此参数的增大,芳环扭角和能隙都缩减而理论压强升高。当理论压强由零压增至3.0 GPa左右时,能隙先快后慢从2.0eV减小至最小值0.87eV。这理论与该聚合物的高压电导测试结果一致。 相似文献
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N. P. Adamov L. N. Puzyrev A. M. Kharitonov E. A. Chasovnikov A. A. Dyadkin A. N. Krylov 《Thermophysics and Aeromechanics》2014,20(6):729-738
The model, experimental equipment, and test program are briefly described. A method of determining the aerodynamic characteristics of the model on the facility with free oscillations is presented. Aerodynamic derivatives of the pitching moment of the model are obtained for two positions of the axis of rotation and Mach numbers M∞ = 2, 4, and 6. At M∞ = 2, the model with the rear position of the axis of rotation is not balanced at low angles of attack, whereas irregular self-sustained oscillations of the model with the frontal position of the axis of rotation arise. 相似文献
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旋转飞行器具有独特的周期性非定常气动现象,其动态特性更加复杂,气流与旋转高度非定常关联,俯仰阻尼导数和Magnus力矩导数同等重要.文章从飞行器气动力建模的理论基础出发,考虑飞行器自转角速度非零的事实,将其作为基态影响参数,重新构建了旋转飞行器气动力数学表达式,并借鉴成熟的常规动导数强迫振动法,采用Fourier级数表征旋转影响,沿用旋转飞行器周期气动等效概念,建立了基于基态旋转流场的周期气动等效平均俯仰动稳定导数、纵向洗流时差导数和滚转动稳定导数获取的原理表达式,并设计了相应的运动模式,可供数值计算和风洞实验使用. 相似文献
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Real-time infrared radiation simulation technology can provide effective support for rapid design and evaluation of a system which integrates infrared imaging technology. Considering the aerodynamic heating effect, this paper presents a real-time infrared radiation characteristic simulation method of aircraft skin based on the panel element method, which can help to assess the infrared radiation impacts of different environment factors and materials. A 3-D model of an aircraft was established and its surface was divided into different parts and panel element meshes to attach material properties. For each mesh, its heat exchange equation is solved so as to obtain the whole skin’s temperature and infrared radiation distribution. The simulation results reveal the influence of different factors on the skin surface radiation, including environmental radiation, aerodynamic heating and material properties. And the credibility and efficiency of the proposed aerodynamic heating simulation method were confirmed by comparing to the CFD simulation results. 相似文献