Turbulence analysis and multiscale correlations between synchronized flow velocity and marine turbine power production

Abstract

The correlation between the flow turbulence and the performances of a marine current turbine is studied. First, the incoming flow encountered in the flume tank is characterized in the framework of fully developed turbulent cascades in the inertial range. The Reynolds number, the Kolmogorov dissipation scale and the integral scale, are estimated from flow measurements. The intermittency of the turbulence is characterized in the lognormal multifractal framework, and the influence of the turbulent flow on the turbine power is assessed. The rotor speed control unit characteristics used for the turbine regulation induces non-negligible effects on the turbine behavior under fluctuations loads. Even if the power spectrum does not reveal any scale invariance, a multiscale analysis allows us to show the correlations between the turbulence time series and the power produced. The classical Mean Square Coherency function shows that for scales larger than 10 s, the upstream velocity and power have large correlations. In the framework of the Empirical Mode Decomposition method, such correlations are studied using the time-dependence intrinsic correlation analysis method. This method allows to zoom into time-frequency scales where the flow perturbations induced some modifications in power production. Highlights ► A high sampling rate of a turbulent flow velocity highlights its multiscale properties. ► There is no power law in the power production Fourier spectrum. ► The intermittency degree of flow velocity increases behind the marine current turbine. ► The coherency is higher in the lower frequencies and reach its minimum at 1 Hz. ► Local correlation analysis spotted a pattern on the loss of correlation.

Three tidal turbines in interaction: An experimental study of turbulence intensity effects on wakes and turbine performance

“…In a previous study [17], Finally, table 2 summarizes these upstream main flow characteristics used in the following sections. .…”

“…where FT (g) means the Fourier transform, FT * (g) its complex conjugate and γ g the auto-correlation function of the signal g(t). The present results are computed from the second part of equation (10), similarly to Durán-Medina et al [17]. The graphics of the left (respectively right) hand side of figure 15 depict S QQ (respectively S T T ) for each of the three configurations and for selected T SR down ∈ [0; 2; 4; 6].…”

“…The same author has previously shown in [15] that the ambient turbulence has a huge impact on the thrust coefficient of the machine, using actuator disc. Durán-Medina et al studies [16,17] have proven the existence of a strong correlation between the fluctuation of velocity due to the ambient turbulence and the fluctuation of the energy production of a turbine. Frost et al [18] also compared power performances for tests performed at laboratory scale and in situ.…”

A stochastic method to account for the ambient turbulence in Lagrangian Vortex computations

“…This PSD appears to converge with respect to the variation σ ( λ) as of σ (λ) = 75% , towards a quasi-linear energy decay. The quality of the PSD curves obtained with sufficient variation on the size of the turbulent structures is further validated by comparison with experimental spectra provided by Medina et al [41] . While the correspondence between numerical and experimental data is not complete, the similarities between these curves is sufficient to conclude that the bering that the smaller the variation σ ( λ), the better the convergence of the numerical TKE towards the target value (see Fig.…”

Susane, a device for sampling chemical gradients in the benthic water column

“…c,d) was determined by the use of a 2D laser Doppler velocimetry (LDV) that acquires point velocity values ( u , v ) in the X and Y directions from the mast (Fig. b) with a sampling rate of at least 100 Hz that detects events of 10 μ m seeding particles (Duran Medina et al ). Automatic displacement tables with a resolution of up to 1 mm are used to place the LDV measurement head at the appropriate positions for velocity profiles in both directions.…”