S. Arunachalam

Interference Factors for Natural Draught Cooling Towers Based on Wind Tunnel Experiments

Wind tunnel experiments were conducted under simulated terrain category 2 for evaluating interference factors using pressure models on four sets of cooling tower models, each when located in tandem. The full-scale dimensions of the cooling towers are 180 m, 165 m, 173m, and 143 m heights with diameters at throat, Dth, of 79 m, 71 m, 70 m and 61 m, respectively. The tower corresponding to 165 m height had a geometric scale of 1:500 and the rest of the models corresponded to 1:300 scale. The model of 165 m tall cooling tower was additionally tested under increased turbulence intensity corresponding to terrain category 3. The tests were conducted for various non dimensionalised spacing, r=a/Dm, ranging from 1.4 to 10, where a is the c/c distance between the models and Dm is the mean diameter, defined as the mean of bottom diameter and Dth. Measurement of pressures was carried out at 30 interval at four levels for all the models. The paper consolidates the data base of experiments conducted at CSIR-SERC to see whether there is a discerning pattern in interference factors that can be recommended for design.

Correlations of aerodynamic pressures for prediction of across wind response of structures

Abstract Correlation length is one of the four important aerodynamic parameters, which is required for prediction of across-wind response of a structure subjected to vortex shedding. Pressure measurement studies on models of three structures with different plan shapes- a circular, an octagonal and an irregular shape, were conducted under simulated open terrain conditions using the boundary layer wind tunnel. This paper presents experimental details and test results on pressure distributions and measurement of correlation lengths. It is shown that for the circular and octagonal models studied, the modified value of rms lift coefficient, C L , V ′ is found to be close to 0.088. Further, for the irregular shaped tower block model also, for the wind angle where the mean across wind force is very small, the value of C L , V ′ is found to be around 0.088. Further research is necessary for validating the value of 0.088 for structures with other cross-sectional shapes.

A Method for Evaluation of Across-Wind Response of a Circular Chimney Including Lock-in Effects and Comparison with ACI Code of Practice

An empirical method for evaluating the across wind response of a tall circular chimney was earlier proposed by authors and a closed form solution was developed for computing the across wind tip deflection. Based on closer review of our earlier equation, it was realized that the suggested equation for computing the overall modal lift force needs to be modified in order to appropriately account for the correlation of forces, and the modification can be brought in the form of a correction factor. After incorporating the correction factor, the across-wind response values are in good agreement with corresponding values obtained by using ACI 307-2008, when applied to three typical chimney examples.