Laser metrology — a diagnostic tool in automotive development processes

Laser measurement techniques are widely used in automotive development processes. Applications at Volkswagen are presented where laser metrology works as a diagnostic tool for analysing and optimising complex coupled processes inside and between automotive components and structures such as the reduction of a vehicle's interior or outer acoustic noise, including brake noise, and the combustion analysis for diesel and gasoline engines to further reduce fuel consumption and pollution. Pulsed electronic speckle pattern interferometry (ESPI) and holographic interferometry are used for analysing the knocking behaviour of modern engines and for correct positioning of knocking sensors. Holographic interferometry shows up the vibrational behaviour of brake components and their interaction during braking, and allows optimisation for noise-free brake systems. Scanning laser vibrometry analyses structure-born noise of a whole car body for the optimisation of its interior acoustical behaviour.Modern engine combustion concepts such as in direct-injection (DI) gasoline and diesel engines benefit from laser diagnostic tools which permit deeper insight into the in-cylinder processes such as flow generation, fuel injection and spray formation, atomisation and mixing, ignition and combustion, and formation and reduction of pollutants. The necessary optical access inside a cylinder is realised by so-called ‘transparent engines’ allowing measurements nearly during the whole engine cycle. Measurement techniques and results on double-pulse particle image velocimetry (PIV) with a frequency-doubled YAG laser for in-cylinder flow analysis are presented, as well as Mie-scattering on droplets using a copper vapour laser combined with high-speed filming, and laser-induced fluorescence (LIF) with an excimer laser for spray and fuel vapour analysis.     

偏振-米散射激光雷达的研制

研制的偏振-米散射激光雷达（PML）,可用于探测卷云和沙尘气溶胶的后向散射光退偏振比以及研究流层大气气溶胶的消光特性。采用窄带滤光片和光阑,将接收到的激光大气回波信号谱线（米散射和瑞利散射光谱）从天空太阳背景噪声中分离出来,以提高系统的白天探测能力。介绍了偏振-米散射激光雷达的结构、技术参数、测量方法和数据处理方法。对偏振-米散射激光雷达的性能参数进行了测定,并对测定结果进行了分析与讨论,给出了偏振-米散射激光雷达对合肥市地区(117.16°E, 31.90°N)上空大气气溶胶的消光特性和卷云的结构、退偏振比垂直廓线以及光学厚度的典型探测结果,对这些结果进行了分析和讨论。结果表明：研制的偏振-米散射激光雷达性能可靠,能对大气气溶胶和卷云的物理和光学特性进行有效的探测。     

大气后向散射比对风速测量的影响

 采用同时测量Rayleigh散射和Mie散射混合信号的多普勒频移的单边缘技术,探测低空中（<12 km）的大气风速。由于大气后向散射比R_b值的变化,导致测量结果有很大的误差。详细分析了Rb值的变化对风速测量灵敏度及测量结果的影响,并做出了在不同Rb值情况下的风速测量校正曲线。结果表明：随着R_b值的增大,风速测量灵敏度有升高的趋势;随着Rb值偏差的增大,测量的风速误差有增大的趋势;同时,在相同的R_b值偏差情况下,随着径向风速的增大,测量的风速误差也有相应的增大。     

Flux-splitting dispersion-relation-preserving dual-compact upwind scheme for solving the Maxwell’s equations on non-staggered grids

This study proposes a flux-splitting Maxwell’s equations solver for modeling electromagnetic waves in two-dimensional non-staggered grids. A fifth-order spatially accurate dual-compact upwind scheme was developed in a three-point grid stencil to approximate the first-order derivative term. The integrity of the proposed finite-difference time-domain method for solving TM-mode Maxwell’s equations verified using two-dimensional test problems. The benchmark Mie-scattering problem was also shown to be in good agreement with the semi-analytic result.