Development of Wind Tunnel and Prototype Testing of Structures

Abstract

Study of wind effect on structure is important for analyzing and designing various components of the structure. Wind effect on structure can be static, dynamic and aerodynamic depending upon dimension and shape of the structure. As wind is dynamic in nature it offers many challenges in its estimation for design of various types of structures. For flexible structures dynamic effect of wind is considered. To understand dynamic effect of wind, it is important to study behaviour of wind under different conditions. A wind tunnel test is performed to characterize wind and its effect on the structures. A wind tunnel is a device which creates a strong, fast and controlled steam of air to study the effect of wind flow on the scaled structure. A wind tunnel has five numbers of basic elements that includes; settling chamber, contraction cone, straight section, test section and diffuser. There are variety of wind tunnel developed to test different types of structures under wind effect. Out of these suction-type wind tunnel is preferred by researchers since it occupies less space and utilize natural air available near the wind tunnel. Development of wind tunnel is quite challenging due to involvement of numerous parameters. Wind tunnel facility becomes a necessity nowadays due to surge in construction of tall buildings, chimneys, suspension cable stayed bridges and flexible towers which requires accurate estimation of wind load on the structures. Though wind tunnel facility is important, but it is a costly facility and then such facility are uncommon. The main objective of the present study is to design and develop an atmospheric boundary layer suction-type wind tunnel to study wind effect on structural models. Civil Engineering Department had a prototype wind tunnel facility made from PVC sheet for qualitative study of structures under wind. A basic understanding about proportioning, functioning and testing requirement was developed from the said facility. A pilot study was conducted to understand functioning, velocity measurement and qualitative testing of structural model. Various literatures; research papers, testing reports, books and guidelines were studied to design various components of the wind tunnel facility. The wind tunnel components designed are; Settling Chamber 1200mm X 1400mm, Contraction Cone 1200mm X 1400mm, Straight Section 450mm X 600mm, Test Section 450mm X 600mm, Diffuser outlet 900mm X 900m. The overall length of the wind tunnel designed is 4.52m. In order to develop low cost wind tunnel facility low cost materials like PVC sheet and acrylic sheet are used to develop diffuser section and straight \& test section, respectively. Only contraction cone is made up of MS sheet material. All sections are assembled seamlessly utilizing rubber gasket to avoid air leakage. An industrial fan is used to circulate air flow in the wind tunnel. Test section of wind tunnel facility is developed to simulate variable wind speed by selecting appropriate exposed area desired using similitude relationship between prototype building and the model. Various relationship in terms of exposed area to corresponding wind speed specified in IS 875(Part-III)-2015 are desired through dimensional analysis. In the current study deformable foam material is used to prepare model of the prototype buildings. Few qualitative studies on the tall buildings are performed to establish functionality of the wind tunnel facility. The spires are one of the element used to simulate atmospheric boundary layer effect on the testing model. The developed wind tunnel facility can further improved for measurement of pressure co-efficient from structural model. A dedicated pressure measurement system is required to be develop for pressure measurement at a point in the wind tunnel. Behaviour of various structural models under the effect of wind can be studied quantitatively.