水滴粒径散射测量中的快速反演方法研究

A Fast Inversion Method for Water Droplet Size Determination in Scattering Light Measurement

针对汽轮机低压缸中水滴的平均尺度的实时测量问题,提出了一种用于从水滴散射光强分布中快速反演水滴粒径参数的半经验理论方法。根据米氏(Mie)散射理论,数值计算了不同水滴尺度对应的散射相函数曲线,并在前向小角度范围内,通过高斯函数拟合得到Mie散射理论的近似解析解,进而拟合得到水滴粒径随高斯函数参数变化的半经验理论公式。在不同条件下,用CCD相机测量得到模拟低压缸内湿蒸汽的散射光强分布图像,通过半经验理论公式快速反演得到水滴群的特征尺寸。结果表明,该方法通过约束水滴特征尺寸的有效范围,得到了散射比与水滴粒径之间简化近似的半经验理论模型,在一定置信范围内可以解决蒸汽湿度的在线测量问题,具有一定的应用价值。

A semi-empirical theoretical method for water droplet size fast calculation is presented to resolve the problem confronted with the measurement of wet steam scattering light distribution in steam turbine.Phase function for different droplet size is numerically calculated based on the Mie scattering theory,and by Gaussian fitting of the phase function curves in the forward small angles,we get an analytic approximation resolution for Mie scattering function.At last,a semi-empirical function for light scattering ratio with the droplet parameters is obtained by further curve fitting.Light scattering experiment for water droplets size measurement is carried out in a simulated steam turbine under various work conditions.Scattering light intensity distribution is received using a CCD camera,and the droplet radium is real-time inversed by means of the semi-empirical function.Because of the restriction of the range of the droplet size distribution and the approximation of the theory,the improved model can well resolve the problem of wet steam droplet parameters online inversion.