Measurements of Turbulence and Flow Structure in the Coastal Ocean using PIV

使用 PIV 测量沿海海洋的湍流和流动结构

• 批准号: 0526486
• 负责人: Thomas Osborn
• 金额: $ 33.99万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-09-01 至 2007-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0526486&HistoricalAwards=false
• 关键词: Measurements; Turbulence; Flow; Structure; Coastal

This project continues our effort to measure the flow structure and turbulence in the bottom 10 m of the water column of the coastal ocean, and study their dependence on elevation, circulation, wave field, bottom topography and stratification. The turbulence measurements were performed using a submersible Particle Image Velocimetry (PIV) system mounted on a telescopic profiling platform with a 10 m profiling range that can align the sample area in any desired direction. The data consist of time series of instantaneous, 2-D velocity distributions in two independent sample areas. The sample areas are spaced to obtain the Reynolds stresses with minimal wave contamination using structure functions. With varying magnifications, the PIV data resolve length scales ranging between 1.2 mm to 1 m, enabling direct calculation of dissipation rate. Preliminary results from the deployments that motivate the present analysis proposal include evidence of: a) Variations of Reynolds stresses and mean current with wave phase. b) Turbulence production lower than the dissipation rate, and variations of stresses with depth in the outer portions of the bottom boundary layer. The stresses seem to scale with the mean current. c) Turbulent energy spectra that increase in similarity to the universal spectrum with increasing Reynolds number, but still indicate anisotropy at all scales, including the dissipation range. e) At moderate, but typical tidal flows, the production is intermittent, occurring during periods of gusts, while the dissipation changes little.Proper modeling of oceanic circulation is essential for improvements in predictions of climate, weather and human impact on the coastal ocean. Transport of pollutants, nutrients and sediment in coastal waters affect many aspects of human life along the coast including the economy, health, tourism, fisheries and food production. It is essential to obtain the knowledge and understanding that leads to development of improved prediction of oceanic transport, circulation and mixing.

该项目继续对近海水柱底部10米处的水流结构和湍流进行测量，并研究它们对海拔、环流、波场、海底地形和层结的依赖关系。湍流测量是使用安装在可伸缩剖面平台上的潜水粒子图像测速(PIV)系统进行的，该平台的剖面范围为10 m，可以将样品区域沿任何所需的方向对准。数据由两个独立采样区的瞬时二维速度分布的时间序列组成。利用结构函数对样本区进行间隔，以获得最小波污染的雷诺应力。在不同的放大倍数下，PIV数据可以分辨1.2 mm到1 m的长度范围，从而可以直接计算耗散率。推动本分析建议的部署的初步结果包括：a)雷诺应力和平均流随波相的变化。B)湍流产生低于耗散率，底部边界层外部应力随深度变化。压力似乎随着平均电流的增加而扩大。C)随着雷诺数的增加，湍流能谱与普适能谱的相似性增加，但在所有尺度上仍显示各向异性，包括耗散范围。E)在温和但典型的潮流中，生产是间歇性的，发生在阵风期间，而消散变化很小。正确的海洋环流模拟对于改进气候、天气和人类对沿海海洋影响的预测至关重要。污染物、营养物和沉积物在沿海水域的运输影响到沿海人类生活的许多方面，包括经济、健康、旅游、渔业和粮食生产。必须获得知识和理解，以改进对海洋运输、环流和混合的预报。