大气扰动及其对飞行的影响

 大气紊流和风切变等现象会影响飞机的飞行品质,并且可能引起严重的飞行事故。本文简要回顾和评述了目前国外研究大气紊流和风切变问题的情况。包括近年来国外在低空大气扰动对飞行影响方面的研究,在改进数学模型、计算与分析方法以及研究与大气扰动有关的飞行品质规范等方面取得的进展。文中同时回顾了我国研究大气扰动对飞行的影响方面的情况。     

Wingtip generated wake vortices as radar target

Previous radar wake vortex detection experiments have resulted in measured beam averaged values of radar reflectivity from wake vortices in clear air. We have employed average wind and thermodynamic variable output from a two dimensional wake vortex model in clear air and fog to predict radar reflectivity in a wake vortex on a one meter grid. The results agree well, compared to data in the literature. In the clear air case, scales of turbulence were analyzed at each grid point to determine the appropriate maximum radar frequency for detection, initial wake structure, transport, and vortex persistence are related to atmospheric winds, atmospheric stability, and generating aircraft characteristics     

Dryden大气紊流模型的数字仿真技术

本文为如何利用电子计算机产生符合Dryden模型的三维大气紊流信号（包括三个速度分量和三个角速度分量）提出了一个比较严格和完整的方法。所得结果的可靠性可以通过相关函数来检验。最后还对飞行模拟器中如何使用这一数学模型提出了一些看法。     

Atmospheric Science with InSight

In November 2018, for the first time a dedicated geophysical station, the InSight lander, will be deployed on the surface of Mars. Along with the two main geophysical packages, the Seismic Experiment for Interior Structure (SEIS) and the Heat-Flow and Physical Properties Package (HP³), the InSight lander holds a highly sensitive pressure sensor (PS) and the Temperature and Winds for InSight (TWINS) instrument, both of which (along with the InSight FluxGate (IFG) Magnetometer) form the Auxiliary Sensor Payload Suite (APSS). Associated with the RADiometer (RAD) instrument which will measure the surface brightness temperature, and the Instrument Deployment Camera (IDC) which will be used to quantify atmospheric opacity, this will make InSight capable to act as a meteorological station at the surface of Mars. While probing the internal structure of Mars is the primary scientific goal of the mission, atmospheric science remains a key science objective for InSight. InSight has the potential to provide a more continuous and higher-frequency record of pressure, air temperature and winds at the surface of Mars than previous in situ missions. In the paper, key results from multiscale meteorological modeling, from Global Climate Models to Large-Eddy Simulations, are described as a reference for future studies based on the InSight measurements during operations. We summarize the capabilities of InSight for atmospheric observations, from profiling during Entry, Descent and Landing to surface measurements (pressure, temperature, winds, angular momentum), and the plans for how InSight’s sensors will be used during operations, as well as possible synergies with orbital observations. In a dedicated section, we describe the seismic impact of atmospheric phenomena (from the point of view of both “noise” to be decorrelated from the seismic signal and “signal” to provide information on atmospheric processes). We discuss in this framework Planetary Boundary Layer turbulence, with a focus on convective vortices and dust devils, gravity waves (with idealized modeling), and large-scale circulations. Our paper also presents possible new, exploratory, studies with the InSight instrumentation: surface layer scaling and exploration of the Monin-Obukhov model, aeolian surface changes and saltation / lifing studies, and monitoring of secular pressure changes. The InSight mission will be instrumental in broadening the knowledge of the Martian atmosphere, with a unique set of measurements from the surface of Mars.     

大气边界层风洞流场特性的模拟

风洞中大气边界层模拟的准确度是保证风洞试验结果准确度的重要因素。本文采用了一种新型曲边梯形尖塔,并结合粗糙元等被动装置对风洞大气边界层模拟进行了研究,模拟出我国规范中的A、B、C和D类四种地貌并将结果和已有的研究结果进行比较。结果显示：所采用新型结构尖塔可以显著提高风洞大气边界层中部以上高度的湍流度,整个湍流度剖面基本覆盖了西方主要国家规范对此项指标的建议值。文中还调试出平均风速剖面不变而湍流度分布可变的流场,为开展相关的结构抗风研究奠定了基础。     

风洞模拟近地面大气边界层

本文通过大气边界层风洞的模拟实验，介绍一种在风洞中模拟近地面大气边界层的方法。根据大风地区的现场实测资料，对大气的风剖面及湍流度等有关参数，提出了一些特殊的要求。常规的模拟方法难以保证与实际风环境的相似，为此专门研制了一种在保证平均风剖面相似的前提下，可使气流产生大湍流度的装置，简称湍流度调节器。通过对模拟边界层的平均风速，湍流度及风速谱的测量分析，证明与实际风区大风环境的风结构相当一致。为解决实     

Measurement and assessment of wind tunnel flow quality

For decades, wind tunnel testing has been conducted in test section environments that have not been adequately or consistently documented. Since wind tunnel flow quality can adversely affect test results, accurate and consistent flow quality measurements are required, along with an understanding of the sources, characteristics, and management of flow turbulence. This paper will review turbulence measurement techniques and data obtained in subsonic, transonic, and supersonic test facilities as they relate to the determination and assessment of wind tunnel flow quality. The principles and practical application of instrumentation used in the measurement and characterization of wind tunnel turbulence will be described. Techniques used for the identification of the sources of wind tunnel disturbances, and the performance of turbulence suppression devices will be outlined. These test techniques will be illustrated with extensive measurements obtained in a number of test facilities. The measurements will provide comprehensive turbulence data that are vital to the assessment and management of flow quality. Procedures designed to assess the potential influence of adverse flow quality on wind tunnel model test performance will also be discussed.     

二维紊流场对飞艇水平面内运动影响研究

大气紊流是影响高空飞艇水平面内巡航的重要原因,传统Dryden模型采用谱分解定理,只能生成一维大气紊流模型,对于高空飞艇复杂的飞行运动来说,生成二维紊流风场模型是必要的.基于紊流场的空间相关特性,采用离散自递归方法构建风场模型,然后结合风速矢量三角形关系式,建立扰动下的飞艇动力学模型,再对该模型进行水平竖直解耦.仿真结果表明,大气紊流作用在飞艇上的力会使飞艇较大程度地偏离其运动航迹,呈不稳定的随机波动状态.因此,构建高空飞艇动力学模型时,要充分考虑大气紊流的影响.     

封闭式薄膜屋盖的参数共振分析

膜结构的非线性风振响应是流固耦合的共同作用问题,当脉动风频率与结构频率满足一定关系时,就有可能出现大幅参数共振。本文首先假定风为无粘性势流,利用室内外空气速度势函数、屋面涡旋以及尾流涡旋来模拟屋面与风场之间的大气湍流边界层。针对封闭式薄膜结构受纵向脉动风荷载作用下,推导了屋面所受的气动力表达式,建立了薄膜屋盖参数振动的非线性力学模型。然后通过数值计算分析,证明了薄膜屋盖在达到临界颤振风速之前有参数共振的可能性。因而,在实际工程中应该考虑出现参数颤振的可能性,通过调整结构参数或预应力,以降低参数共振的频率范围。     

Multi-Scale Plasma Turbulence in the Diffuse Interstellar Medium

I discuss how radioastronomical observations can provide information on the turbulence that governs the propagation of cosmic rays in the Galaxy. Interstellar radio wave propagation effects, collectively referred to as interstellar scintillations, yield information on the spatial power spectra of fluctuations in plasma density and magnetic field. Results of relevance to cosmic-ray physics are the existence of interstellar turbulence over a wide range of spatial scales (which can thus interact with a wide range of cosmic ray energies), the detection of magnetic field fluctuations in association with this turbulence, and a change in the nature of the turbulence on spatial scales of about 3.5 parsecs. A number of mysteries remain, such as the apparent suppression of Fast Magnetosonic wave generation by the interstellar turbulence.     

Statistical Analysis of Velocity Measuring Systems Employing the Photon Correlation Technique

Velocities of fluid flows and solid objects can be measured by performing photon count correlations on laser light scattered from the measuring region, the most common optical configuration being the laser Doppler system. A statistical analysis for the counting process is presented for both the constant velocity case and for turbulent fluid flows with formulations for specific laser Doppler configurations. For turbulent flow, relationships are derived for the shape of the count correlation in terms of the mean velocity and rms turbulent intensity, taking into account the shape of the turbulence correlation curve. Experimental results recorded for both a constant velocity solid object and for an unseeded turbulent air flow in a wind tunnel are presented, and, in the latter case, comparisons are made with hot-wire measurements.     

A long-range laser velocimeter

A long-range laser velocimeter (LV) developed for remote operation from within the flow fields of large wind tunnels is described. Emphasis is placed on improvements in optical hardware as well as additions to data acquisition and processing techniques. The method used for data reduction of photon resolved signals is outlined in detail, and measurement accuracy is discussed. To study the performance of the LV and verify the measurement accuracy, laboratory measurements were made in the flow field of a 10-cm-diameter, 30-m/s axisymmetric jet. The measured velocity and turbulence intensity surveys are compared with measurements made with a hot-wire anemometer. Additionally, the LV was used during the flow calibration of the 80-ft×120-ft wind tunnel to measure the test-section boundary layer thickness at the maximum wind tunnel speed of 51.5 m/s. The requirements and techniques used to seed the flow are discussed, and boundary-layer surveys of mean velocity and turbulence intensity of the streamwise component and the component normal to the surface are presented. The streamwise component of mean velocity is compared with data obtained with a total pressure rake     

Retrieval of a wind profile from the Galileo Probe telemetry signal

Ultrastable oscillators onboard the Galileo Probe and Orbiter will permit very accurate determinations of the frequency of the Probe's telemetry signal as the Probe descends from a pressure level of several hundred mb to a level of about 20 bars. Analysis of the time-varying frequency can provide, in principle, a unique and important definition of the vertical profile of the zonal wind speed in the Jovian atmosphere. In this paper, we develop a protocol for retrieving the zonal wind profile from the Doppler shift of the measured frequency; assess the impact of a wide range of error sources on the accuracy of the retrieved wind profile; and perform a number of simulations to illustrate our technique and to assess the likely accuracy of the retrieval.Because of unavoidably large uncertainties in the absolute frequencies of the oscillators, we use time-differenced frequencies in our analysis. Nevertheless, it is possible to recover absolute wind speeds as well as wind shears, since the Orbiter/Probe geometry changes significantly during the Probe relay link. We begin with the full relativistic Doppler shift equation. Through the use of power series expansions and a basis function representation of the wind profiles, we reduce the basic equation to a set of linear equations that can be solved with standard linear least-squares techniques.There are a very large number of instrumental and environmental factors that can introduce errors into the measured signal or to the recovery of zonal winds from the data. We provide estimates of the magnitudes of all these error sources and consider the degree to which they may be reduced by a posteriori information as well as the results of calibration tests. The most important error source is the a posteriori uncertainty in the Probe's entry longitude. The accuracy of the retrieved winds is also limited by errors in the Probe's descent velocity, as obtained from atmospheric parameters measured by several Probe experiments, and in the a posteriori knowledge of secular drifts in the oscillators' frequencies during the relay link, due, for example, to aging and radiation damage.Our simulations indicate that zonal winds may be retrieved from the Doppler data to an accuracy of several m s^-1. Therefore, it may be possible to discriminate among alternative models for the basic drive of the zonal winds, since they differ significantly in the implied zonal wind profile.     

MHD structures, waves and turbulence in the solar wind: Observations and theories

A comprehensive overview is presented of recent observational and theoretical results on solar wind structures and fluctuations and magnetohydrodynamic waves and turbulence, with preference given to phenomena in the inner heliosphere. Emphasis is placed on the progress made in the past decade in the understanding of the nature and origin of especially small-scale, compressible and incompressible fluctuations. Turbulence models to describe the spatial transport and spectral transfer of the fluctuations in the inner heliosphere are discussed, and results from direct numerical simulations are dealt with. Intermittency of solar wind fluctuations and their statistical distributions are briefly investigated. Studies of the heating and acceleration effects of the turbulence on the background wind are critically surveyed. Finally, open questions concerning the origin, nature and evolution of the fluctuations are listed, and possible avenues and perspectives for future research are outlined.     

网格湍流CAARC模型风洞实验

对大气湍流边界层的真实模拟是风工程风洞模拟实验所要满足的基本条件之一，平均速度剖面，湍流度剖面，积分尺度和风谱是反映大气湍流边界层流动的四个最基本的因素。本文首先研究了不同孔隙率的均匀网格湍流场的流动特性，得到湍流度，积分尺度以及风谱的变化规律，然后在变化基中某一个因素而保持另外三个因素不变的条件下，研究了处于均匀网格湍流场中的CAARC模型风荷载响应的变化，从而确定每个因素的独立变化对模型所受风荷的影响。实验结果表明湍流度和积分尺度对结构物所受风载都有很重要的影响，在风洞大气湍流边界层模拟中应该予以充分的考虑，否则将会引起风荷载实验结果的偏差。     

正弦型来流条件下大气表面层特性的研究

导出了正弦来流条件下的大气表面层平均风速及湍流强度的计算式。在环境风洞中使用粒子图像速度仪（PIV）对正弦来流条件下的大气表面层平均风速廓线和湍流强度进行了测量。结果表明：正弦型来流条件下所模拟的大气表面层在不同高度上风速均呈正弦规律波动,测量得到平均风速与导出计算式结果一致,相当于在定常风速廓线基础上叠加一个周期与主流风速一致、振幅随高度变化的正弦波动函数。每一个相位的湍流强度沿高度的分布均与定常来流条件下的湍流强度有着相似的变化规律,且湍流强度的大小随相位变化呈现一定的波动性。     

The consequences of micropulsations on geomagnetically trapped particles

Non-adiabatic radiation belt dynamics is largely controlled by interactions between geomagnetically trapped particles and various modes of plasma turbulence. Long period electric field fluctuations act as a major source mechanism for the inner zone through the process of inward radial diffusion of particles injected into the convection dominated outer zone. Higher frequency turbulence provides a major loss mechanism by pitch-angle scattering into the atmospheric loss cone. The wave particle interactions may take the form of self induced instabilities or parasitic scattering. Examples of each will be given in this review.     

Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI): Instrument Design and Calibration

The Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument was built for launch and operation on the NASA Ionospheric Connection Explorer (ICON) mission. The instrument was designed to measure thermospheric horizontal wind velocity profiles and thermospheric temperature in altitude regions between 90 km and 300 km, during day and night. For the wind measurements it uses two perpendicular fields of view pointed at the Earth’s limb, observing the Doppler shift of the atomic oxygen red and green lines at 630.0 nm and 557.7 nm wavelength. The wavelength shift is measured using field-widened, temperature compensated Doppler Asymmetric Spatial Heterodyne (DASH) spectrometers, employing low order échelle gratings operating at two different orders for the different atmospheric lines. The temperature measurement is accomplished by a multichannel photometric measurement of the spectral shape of the molecular oxygen A-band around 762 nm wavelength. For each field of view, the signals of the two oxygen lines and the A-band are detected on different regions of a single, cooled, frame transfer charge coupled device (CCD) detector. On-board calibration sources are used to periodically quantify thermal drifts, simultaneously with observing the atmosphere. The MIGHTI requirements, the resulting instrument design and the calibration are described.     

The Huygens Doppler Wind Experiment ' Titan Winds Derived from Probe Radio Frequency Measurements

A Doppler Wind Experiment (DWE) will be performed during the Titan atmospheric descent of the ESA Huygens Probe. The direction and strength of Titan's zonal winds will be determined with an accuracy better than 1 m s⁻¹ from the start of mission at an altitude of ∼160 km down to the surface. The Probe's wind-induced horizontal motion will be derived from the residual Doppler shift of its S-band radio link to the Cassini Orbiter, corrected for all known orbit and propagation effects. It is also planned to record the frequency of the Probe signal using large ground-based antennas, thereby providing an additional component of the horizontal drift. In addition to the winds, DWE will obtain valuable information on the rotation, parachute swing and atmospheric buffeting of the Huygens Probe, as well as its position and attitude after Titan touchdown. The DWE measurement strategy relies on experimenter-supplied Ultra-Stable Oscillators to generate the transmitted signal from the Probe and to extract the frequency of the received signal on the Orbiter. Results of the first in-flight checkout, as well as the DWE Doppler calibrations conducted with simulated Huygens signals uplinked from ground (Probe Relay Tests), are described. Ongoing efforts to measure and model Titan's winds using various Earth-based techniques are briefly reviewed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Geology and Physical Properties Investigations by the InSight Lander

Although not the prime focus of the InSight mission, the near-surface geology and physical properties investigations provide critical information for both placing the instruments (seismometer and heat flow probe with mole) on the surface and for understanding the nature of the shallow subsurface and its effect on recorded seismic waves. Two color cameras on the lander will obtain multiple stereo images of the surface and its interaction with the spacecraft. Images will be used to identify the geologic materials and features present, quantify their areal coverage, help determine the basic geologic evolution of the area, and provide ground truth for orbital remote sensing data. A radiometer will measure the hourly temperature of the surface in two spots, which will determine the thermal inertia of the surface materials present and their particle size and/or cohesion. Continuous measurements of wind speed and direction offer a unique opportunity to correlate dust devils and high winds with eolian changes imaged at the surface and to determine the threshold friction wind stress for grain motion on Mars. During the first two weeks after landing, these investigations will support the selection of instrument placement locations that are relatively smooth, flat, free of small rocks and load bearing. Soil mechanics parameters and elastic properties of near surface materials will be determined from mole penetration and thermal conductivity measurements from the surface to 3–5 m depth, the measurement of seismic waves during mole hammering, passive monitoring of seismic waves, and experiments with the arm and scoop of the lander (indentations, scraping and trenching). These investigations will determine and test the presence and mechanical properties of the expected 3–17 m thick fragmented regolith (and underlying fractured material) built up by impact and eolian processes on top of Hesperian lava flows and determine its seismic properties for the seismic investigation of Mars’ interior.