风成沙纹发育过程中形态变化的风洞实验研究

Wavelength and Height of Aeolian Ripple in a Wind Tunnel

在四种风速条件下,对沙纹形成过程中的形态变化进行了风洞实验研究,讨论了沙纹宽度、沙纹迎风坡宽度、沙纹背风坡宽度、沙纹高度和沙纹指数与风速和输沙量的关系.研究发现沙纹发育呈现阶段性特点,沙纹宽度变化与输沙量的对数值成正比,沙纹迎风坡宽度和背风坡宽度与沙纹宽度成线性关系,沙纹稳定高度与沙纹高度之差和输沙量与风速之比成负指数关系.随着风速的增大沙纹稳定高度减小.沙纹稳定高度与沙粒蠕移距离随高度变化的幅度有关.沙纹指数综合反映了沙纹宽度及沙纹高度与输沙量和风速的关系.文中给出了上述形态参数与输沙量或风速的具体函数表达式.

Controls on the shape of aeolian ripple during its development are investigated experimentally in a wind tunnel. The experiments were conducted with one test sand and four different stream velocities. For each wind velocity, the shape parameters of ripples, including wavelength, height, stoss length and lee length, were measured during the processes of ripple development. The measured data exhibit that ripple wavelengths increase logarithmically with cumulated rate of sand transport rather than with directly wind velocity. There is linear relationship between wavelength and stoss length or lee length. The differences of ripple waveheight and its maximum (steadystate waveheight) decay exponentially with the ratio of cumulated rate of sand transport to wind velocity. The steadystate waveheight of sand ripple, depending on change in the length of grain repation with height on the stosssurface of ripple, decrease with the rise of wind velocity, which is different at large from the existing views and offers an explanation for different results of ripple in the literature. Ripple index reflects the compound relationship of ripple wavelength and height to the cumulated rate of sand transport and wind velocity. The specific expressions for shape parameter can be found in the text.