A Comparison of Turbulence Generated by 3DS Sparse Grids With Different Blockage Ratios and Different Co-Frame Arrangements

Effects of blockage, arrangement and channel dynamics on performance of turbines in a tidal array

The performance and economics of turbines in a tidal array are largely dependent on the power per turbine, and so approaches that can increase this power are crucial for the development of tidal energy. In this paper, we combine a two-scale partial array model and a one-dimensional channel model to investigate the effects of blockage, turbine arrangement, and channel dynamics on tidal turbines. The power per turbine is obtained as the product of two parameters: a power coefficient measuring the power acquired from the instantaneous flow and an environment coefficient showing the response of th…

Beyond the Betz Theory - Blockage, Wake Mixing and Turbulence

Recent analytical models concerning the limiting efficiency of marine hydrokinetic (MHK) turbines are reviewed with an emphasis on the significance of blockages (of local as well as global flow passages) and wake mixing. Also discussed is the efficiency of power generation from fully developed turbulent open channel flows. These issues are primarily concerned with the design/optimization of tidal turbine arrays; however, some of them are relevant to wind turbines as well.

风电场整体阻塞作为逆压梯度问题：模型风电场感应区的湍流增强与频谱修正

Wind farm global blockage as an adverse pressure gradient problem: turbulence amplification and spectral modification in the induction region of a model wind farm

本研究通过实验将风电场感应区视为逆压梯度湍流边界层问题，发现风电场引起的大尺度湍流增强主要源于逆压梯度，且与转子尺度相当的湍流能量对涡轮疲劳载荷有重要影响。

A turbulent premixed flame on fractal-grid generated turbulence

A space-filling, low blockage fractal grid is used as a novel turbulence generator in a premixed turbulent combustion experiment. In contrast to the power law decay of a standard turbulence grid, the downstream turbulence intensity of the fractal grid increases until it reaches a peak at some distance from the grid before it finally decays. The effective mesh size and the solidity are the same as those of a standard square mesh grid with which it is compared. It is found that, for the same flow rate and stoichiometry, the fractal generated turbulence enhances the burning rate and causes the fl…

Turbulence without Richardson-Kolmogorov cascade

We present an experimental investigation of intense turbulence generated by a class of low-blockage space-filling fractal square grids. We confirm the existence of a protacted production region followed by a decaying region, as first reported by Hurst & Vassilicos (Physics of Fluids, 2007). We show that the centerline streamwise variation of most of the statistical properties of the turbulent flow can be scaled by a wake interaction length-scale $x_*$. We also confirm the finding of Seoud and Vassilicos (Physics of Fluids, 2007) that the ratio of the integral length-scale $L_u$ to the Taylor m…

The decay of turbulence generated by a class of multi-scale grids

A new experimental investigation of decaying turbulence generated by a low-blockage space-filling fractal square grid is presented. We find agreement with previous works by Seoud & Vassilicos (2007) and Mazellier & Vassilicos (2010) but also extend the length of the assessed decay region and consolidate the results by repeating the experiments with different probes of increased spatial resolution. It is confirmed that this moderately high Reynolds number Reλ turbulence (up to Reλ {\simeq}350 here) does not follow the classical high Reynolds number scaling of the dissipation rate ε ~ u'^3/L and…