Clustering techniques are of main interest for separation of partial discharge (PD) sources. The separation is achieved if it is possible to extract from the PD pulses specific information related to the source. In this sense, this paper explores the capability of fundamental quantities derived from PD current pulses such as the peak amplitude Ipeak, the apparent charge Q, and the energy E as parameters intended for source separation. For this purpose, an unconventional PD measuring circuit is used to acquire PD pulses from several laboratory test objects. Once the pulses are digitized and stored, the values of Ipeak, Q, and E are computed according to the proposed methods in time and frequency domain. A theoretical analysis is presented to illustrate how values of Ipeak, Q and E can be related to the pulse shape so that they can be used as source separation parameters. Then, the IpeakQE clusters are computed for laboratory measurements. The results showed that these parameters are suitable for separation of sources provided that the pulse shapes are different. This cluster technique was also proved to be independent of the change of the acquisition parameters that are relevant for unconventional measuring systems. In addition, the easiness of the quantities computation makes the clustering technique introduced in this paper feasible for practical applications.@en

The acquisition parameters of an unconventional Partial Discharge (PD) measuring system affect the way the PD pulses are recorded and in turn, the results of the data processing. The noise based on the oscilloscope's vertical resolution is a feature of the sampled signal that is always present when a digital acquisition system is used. In PD unconventional systems, several parameters such as the sampling frequency Fs, the acquisition time T, the number of samples N and the vertical resolution VR of the digitizer result in a wide oscilloscope-based noise variation, that could be quantified by the signal to noise ratio (snr). The classification map is a tool that came available with the development of unconventional systems, that due to their wide bandwidth are able to resolve PD pulses in time and apply clustering techniques for PD source separation. The equivalent time T_eq and equivalent bandwidth W_eq, used to plot the classification map, attempts to extract features of the PD pulses to form clusters so that classification of sources can be achieved. The classification map is based on the ability of separating PD sources by resorting to the parameters T_eq and W_eq, that are believed to show significant differences for distinct PD sources, while they are clearly consistent for the same source. This paper conducts a set of theoretical analysis and laboratory measurements to evaluate the influence of the oscilloscope-based noise on the results of T_eq and W_eq. The results proved that the classification map is heavily influenced by the signal to noise ratio.

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The current paper presents the effort, in the EU AVATAR project, to establish the necessary requirements to obtain consistent lift over drag ratios among seven CFD codes. The flow around a 2D airfoil case is studied, for both transitional and fully turbulent conditions at Reynolds numbers of 3 × 10⁶ and 15 × 10⁶. The necessary grid resolution, domain size, and iterative convergence criteria to have consistent results are discussed, and suggestions are given for best practice. For the fully turbulent results four out of seven codes provide consistent results. For the laminar-turbulent transitional results only three out of seven provided results, and the agreement is generally lower than for the fully turbulent case.

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