Enforcing Bladed to Use Turbulent Wind Without Time Shift

In a case where users want Bladed not to apply any turbulent wind time shift in Bladed calculations, it is possible to do that using the guidance provided in the present article. This is relevant if one is interested in the exact time series of the wind itself, not just the statistics, for example when using Generate turbulence to match a measured wind time history at one grid point option, see advanced options in generating turbulent wind fluctuations. Two parameters need to be set in Bladed to enable this effect: by allowing turbulence wrapping and by setting the required turbulent wind start time.

Figure 1 depicts the mechanism to disregard the turbulent wind time shift in Bladed time domain calculations. It can be seen that the start of Bladed calculations can be matched with the start of the turbulent wind file by manipulating the starting time of turbulent wind file. This way, the "recycled" part of the turbulent wind will be used as the starting point of Bladed calculations.

Figure 1: Illustration an approach to disregard the turbulent wind time sift in Bladed time domain calculations. (a) A case where time shift is automatically applied and (b) mechanism for disregarding the time shift. The approach makes use of the the turbulence wrapping and turbulent wind start time functionalities.

Mathematically, the required value of the turbulent wind start time (\(t_{start}\) as described in the turbulent wind start time) to achieve the desired effect is formulated as:

\[ \begin{equation} \label{eq:NotUsingTimeShiftStartTime} t_{start} = T^{wind} - t_{shift}, \end{equation} \]

and

\[ \begin{equation} \label{eq:NotUsingTimeShiftBufferTime} t_{shift} = \dfrac{x_{shift}}{U_{ref}}. \end{equation} \]

The turbulent wind time shift, \(t_{shift}\), can be calculated by relating the Mean wind speed value (\(U_{ref}\)) with the length of time shift (\(x_{shift}\)), see again the description of the turbulent wind time shift. Variable \(T^{wind}\) represents the total length of the turbulent wind file (from the .wnd file) before the turbulence wrapping is done.

The procedure can be summarised in the following steps:

• Activate the turbulence wrapping in Bladed,
• Obtain the total duration of the turbulent wind file \(T^{wind}\),
• Calculate the length of time shift (\(x_{shift}\)) automatically added by Bladed as described in the turbulent wind time shift procedure,
• Calculate the time shift automatically added by Bladed using Equation \(\eqref{eq:NotUsingTimeShiftBufferTime}\),
• Set the appropriate value of turbulent wind start time in Bladed with \(t_{start}\) in Equation \(\eqref{eq:NotUsingTimeShiftStartTime}\).

Last updated 28-08-2024