Coherence characteristics of fluctuating lift forces for rectangular shape with various fairing decks

This paper presents improved empirical functions for the coherence of wind forces that can be applied in gust response analysis under any conditions. Earlier studies pointed out the discrepancy between the coherence model that is usually used in gust response analysis and measured coherence, which is affected by the girder shape and turbulence properties. Although a multichannel pressure measurement test is required for evaluating coherence in an individual condition, it needs sophisticated experimental equipment. Therefore, a coherence function that can be used regardless of the conditions is strongly needed. In order to provide such a coherence function, multiple pressure measurement tests are conducted for rectangular shape with various fairing decks in smooth flow and grid turbulence, and the coherence characteristics are investigated using considerable experimental data. Universal characteristics have been found that are independent of the girder shape and turbulence properties, and empirical functions are proposed based on these characteristics. Parameters in the empirical function have uniform distributions over the properly non-dimensionalized axis, and they can be defined only by the two types of flow patterns around girders. The proposed empirical functions offer significant improvements over coherence as proposed in earlier studies in this area.