G. Ramesh Babu

Experimental Determination of Wind-Induced Response on a Model of Natural Draught Cooling Tower

The detailed and well-publicized documented paper by Bamu and Zingoni in 2005 on cooling-tower collapses accentuates the effect of wind on the performance of cooling towers. As it is well established that wind-tunnel tests on tower models result in a more realistic assessment of wind-induced stresses, wind-tunnel tests are conducted on aero-elastic model of an isolated cooling tower and the cooling tower with surrounding structures. The details of the experimental programme, measurements, analysis, and results for both the isolated and interference cases are presented in this paper. Based on the analysis of experimental data, ring-resonance frequencies, and mode shapes of the model, meridional (Nϕ) and hoop (Nθ) stress resultants and interference factor due to the presence of surrounding buildings are evaluated. The values of Nϕ, Nθ, ring-resonance frequencies, and mode shapes for isolated model are further compared with the values obtained based on finite element analysis.

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.

CFD and Wind Tunnel Investigations on Rectangular Building with Corner Cuts

Aerodynamic modifications at corners are considered an effective countermeasure to minimize the wind-induced load and load effects. One of the effective corner modification measures is provision of corner cuts to reduce wind-induced along-wind loads and cross-wind vibrations of the building. However, the corner modifications are provided usually throughout the height of the building. The present study deals with the effect of providing corner cuts over limited heights from top of the building. A 1:2:5 rectangular building has been considered for the present study. A corner cut size of 7.5% has been considered. To study the effect of spread over of corner cut over the height of the building, a total number of four cases have been considered, viz. (i) building with full-height corner cut, (ii) building with half-height corner cut, (iii) building with one-third-height corner cut and (iv) building with no corner cut. The study is carried out by using both computational fluid dynamics and wind tunnel experiments. CFD studies included angles of wind incidence of 0° and 90° under open terrain condition. The wind tunnel investigations included pressure measurements on a rigid model with 1:300 geometric scale under simulated open terrain condition for angles of wind incidence of 0°, 45° and 90°. Using the measured pressures, pressure coefficients, drag and lift force coefficients have been evaluated. The effectiveness of the corner cut over different heights of the building model has been studied by comparing the evaluated aerodynamic coefficients. Further, numerical results are compared with experimental results for validation purpose.

Wind Tunnel Investigations on a Tall Building With Elliptic Cross Section

According to a statistics revealed by Council of Tall Building and Urban Habitat [1] that for every 11.5 millions of global population, there is one tall building with 200 m+ in height available globally. Tall building constructions are paving ways for rapid urbanization worldwide including India, especially during the last one decade and will be continued over next few decades. Wind loads are one of the most important loads that govern the design of tall buildings. Published data on pressure and force coefficients for 3-D building with elliptic cross section under boundary layer flows are very scanty. This paper presents the results on mean force coefficients obtained through wind tunnel pressure measurements carried out on a 3-D tall building with elliptic cross section for various angles of wind incidence under suburban terrain. It is found that the mean pressure distributions and force coefficients depend significantly upon the angle of wind incidence.

Evaluation of Mean Wind Force Coefficients for High-Rise Building Models with Rectangular Cross-Sections and Aspect Ratio’s of 6 and 8

Studies on measurement of wind loads on rigid models (geometric scale of 1:300) of tall rectangular high-rise buildings having plan dimensions of 7.5 cm (b) × 15 cm (d) with two different heights (h) of 45 cm and 60 cm, under simulated open terrain condition was carried out using Boundary Layer Wind Tunnel (BLWT) facility at CSIR-SERC, Chennai. The measurements of mean base forces (\( {\bar{\text{F}}}_{\text{x}} \), \( {\bar{\text{F}}}_{\text{y}} \) and \( {\bar{\text{F}}}_{\text{z}} \)) and torsions (\( {\bar{\text{T}}}_{\text{x}} \), \( {\bar{\text{T}}}_{\text{y}} \) and \( {\bar{\text{T}}}_{\text{z}} \)) were made using a six-component force/torque sensor for 8 different angles of wind incidence (θ), ranging from 0° to 90° and for 4 various mean wind velocities (\( {\bar{\text{U}}}_{\text{ref}} \)). Based on the analysis, mean base forces/torsions in three mutually perpendicular axes, mean force coefficients in body fixed axes X and Y, mean drag, lift force and torsion coefficients were obtained corresponding to reference mean pressures measured at top of the building. It is observed that the magnitudes of measured forces/torsions for model with h/b = 8 are found to be high when compared with forces for model with h/b = 6. The evaluated values of mean force coefficients obtained from the present study were compared with the values reported in IS: 875 and found that the values given in code are found to be conservative. Further, the % difference between them is observed to be within 5 %, especially for wind direction normal to longer width of models with h/b = 6 and 8, respectively.

Wind Induced Interference Effects on a Row of Three Buildings with Irregular Plan Shape

P. Harikrishna, A. Abraham, S. Selvi Rajan, G. Ramesh Babu, S. Chitra Ganapathi, and Nagesh R. Iyer Principal Scientist, CSIR-Structural Engineering Research Centre, Chennai, TN, India, hari@serc.res.in Senior Scientist, CSIR-Structural Engineering Research Centre, Chennai, TN, India, abraham@serc.res.in Chief Scientist, CSIR-Structural Engineering Research Centre, Chennai, TN, India, sselvi@serc.res.in Principal Scientist, CSIR-Structural Engineering Research Centre, Chennai, TN, India, gramesh@serc.res.in Scientist, CSIR-Structural Engineering Research Centre, Chennai, TN, India, chitrag@serc.res.in Director, CSIR-Structural Engineering Research Centre, Chennai, TN, India, nriyer@serc.res.in