Designs of buildings are changing with emerging demands of several aesthetical features and efficient design based on geometry. Development of new building materials and construction techniques have enabled us to build new buildings which are tall and unsymmetrical, but unfortunately such structures are more susceptible to wind loads. Thus it becomes necessary to estimate wind loads with higher degree of confidence. Although ample information regarding wind load on symmetrical and regular structure is available in various international codes, they lack the study of effect of wind forces on unsymmetrical structures. This paper presents experimental and numerical studies of the wind effect on commonly used C-shaped buildings with varying aspect ratio and its optimization caused by the alteration of angle of incidence. Furthermore, results obtained by numerical analysis have been validated with the experimental one. For this study, numerical analysis has been carried out using ANSYS Fluent with
Gradual increase of demand of tall and unsymmetrical buildings with efficient geometric design and planning needs futuristic visionary and scientific estimates of various kinds of forces. Wind force is one of them, which plays a crucial role in case of unsymmetrical buildings. Shortage of land and demand of good aesthetical view have forced us to construct nonconventional plan-shaped building. Although ample information regarding wind load on symmetrical structure (conventional plan-shaped structure) is available in various international codes, for example, IS: 875 (Part 3): 1987(code of practice for wind loads for buildings and structures) [
Though now a days nonconventional plan shapes are very common building configurations, experimental as well as numerical data for such shapes for different wind directions are very limited. Various literatures provide the study of effect of wind pressure on tall and irregular shape of buildings. Paterson and Apelt [
In present study, numerical as well as experimental analysis has been carried out on irregular shape, i.e., C-shaped of the building for wind incidence angle of 0° to 180° at the interval of 30°. ANSYS FLUENT is used to numerically model the domain and study the wind flow, and experimental data were obtained by using wind tunnel. The main purpose of this paper is to assess the change in wind pressure on different faces of C-shaped model due to change in wind angle and aspect ratio (height) of the building by experimental analysis and numerical analysis, and then those results were validated. Validation of results is necessary because there is no such direct reference from where wind pressure on the irregular shape of the building could be calculated. So, it becomes necessary to compare the experimental and numerical data.
Experiments are carried out in an open circuit subsonic wind tunnel in the Aerodynamics Laboratory of the Department of Aerospace Engineering, Indian Institute of Technology Kharagpur, India. The wind speed is kept constant at 12.9 m/s. The wind tunnel with a bottom surface made up of plywood, a test section is 1.83 m long, and cross-sectional dimensions of 0.61 m × 0.61 m. Models are placed within the boundary layer zone, centrally in the test section at a distance of 1.2 m from the beginning of the test section. To ascertain models within the boundary layer zone, wooden cubic blocks of 25 mm size, and clear spacing of 50 mm in all directions are fixed on a 4 mm thick plywood sheet as shown in Figure
The schematic diagram of wind tunnel.
The experimental models are made of transparent Perspex sheet of 3 mm thickness. Details of the two C-shaped models, as C-1 and C-2 of varying height ratios configurations, are shown in Figures
(a–c) Isometric view of C-1- and C-2-shaped building model and pressure-tapping locations along the periphery of models.
Details of building models with different aspect ratios.
Sl. No. | Overall depth, |
Depth, |
Overall breadth, |
Breadth, |
Height, |
Plan area, (mm2) | Radius of curvature, |
(1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) |
|
|||||||
C-1 | 120 | 90 | 120 | 60 | 70 | 11613 | 30 |
C-2 | 120 | 90 | 120 | 60 | 60 | 11613 | 30 |
Photograph of C-shaped building model in the test section.
The models are fitted with 90 to 120 numbers of pressure-tapping points in 4-5 rows and 3–5 columns on the surfaces. The pressure-tapping points are kept at less spacing near the wall boundaries to tap the sharp pressure variation due to flow separation and at larger spacing in the middle of the surfaces.
Free stream velocity during the experiment is measured with the help of the pitot tube. The models are fitted with 90 to 120 numbers of pressure-tapping points in 4-5 rows and 3–5 columns on the surfaces. The pressure-tapping points are kept at less spacing near the wall boundaries to tap the sharp pressure variation due to flow separation and at a larger spacing in the middle of the surfaces. The free ends of tubes are connected to Digital Sensor Array (DSA) to record the fluctuating wind pressure at the corresponding tapping points. All data are measured by a DSA scan valve corporation, model DSA 3217/16 pox, USA. This DSA device is set to give an average pressure of 5 s duration. At the same time, for greater accuracy, a pressure measurement at each tapping point is repeated for three times, and the mean of three pressure data are obtained. The pressure coefficient
Numerical simulations have been carried out in this study using ANSYS Fluent using the computational fluid dynamic (CFD) technique, based on the control volume method. The RNG
It is advantageous to use the ( The first transported variable determines the energy in the turbulence and is called turbulent kinetic energy ( The second transported variable is the turbulent dissipation (
The
For numerical analysis, the models of C-shaped buildings of different aspect ratios have been created in ANSYS and then analysed by using the
Data considered in numerical analysis: Types of fluid: air Density of air: 1.225 Kg/m3 Viscosity of air: Turbulence model: Solver: pressure-based
The domain size as shown in Figures
(a, b) Domain for the plan and elevation.
The finite volume discretization approach is used to discretize the whole domain so that separation of wind flow, upwash, and downwash mechanisms can happen similar to the experimental study. The discretization (meshing) of the C-shaped model is shown in Figure
Meshing of C-shaped model.
For completing numerical modelling and simulation, there are several boundary conditions which are considered. The flow parameter at inlet, outlet wall, and surface are needed to be considered. At inlet, the velocity of flow is 12.9 m/s, and the same velocity is provided for experimental procedure so that the result could be compared. The flow velocity at inlet is along the positive
Pressure variation on the building is directly influenced by wind flow pattern. Vortex generation and different types of mechanism such as separation of flow, upwind, and downwind happen due to dynamic behavior of wind flow. To investigate such mechanisms more accurately, wind flow patterns around the C-shaped building are being studied for different angle of incidences varying from 0° to 180° at an interval of 30° using the CFD technique. Flow pattern for different angles of incidences are shown in Figures
Wind flow pattern for different wind incidence angles. (a) 0°. (b) 30°. (c) 60°. (d) 90°. (e) 180°.
Wind is directly affecting Face C for wind incidence angle 0° to 180°, respectively, so the pressure distribution is symmetrical about vertical axis, and vortices generated at the wake region are also symmetrical for both the cases (Figure
The study of pressure coefficient is necessary in every unconventional-shaped building which is designed under wind excitation. Chakraborty et al. [
Pressure contour on different faces are plotted for every angle of incidence. Some pressure contours are shown in Figures
Pressure contour on different faces of the C-1 model at different wind angles. (a) Face A 90°. (b) Face B 45°. (c) Face C 0°. (d) Face G 90°. (e) Face H 180°. (f) Face I 90°.
Pressure contour on different faces of the C-2 model at different wind angles. (a) Face A 90°. (b) Face B 45°. (c) Face C 0°. (d) Face G 90°. (e) Face H 180°. (f) Face I 90°.
Mean pressure coefficients for all the faces of the C-1 model. (a) Experimental study. (b) Numerical study.
Mean pressure coefficients for all the faces of the C-2 model. (a) Experimental study. (b) Numerical study.
Figures
Pressure variation and mean pressure coefficients of all the faces of C-1 and C-2 models are also studied numerically in detail by CFD for different wind incidence angles. It can be seen clearly that numerically predicted pressure contours are converged well with the experimentally predicted results. But, very less variation in mean pressure coefficients are observed with respect to the experimental results (Figures
Error analysis is also performed by obtaining mean percentage error (ME), standard deviation (SD), coefficient of determination (
Percentage of mean error for different faces of the building.
Error analysis of predicted
Face |
|
MAE | RMSE | MAPE |
---|---|---|---|---|
A | 0.99 | 0.234 | 0.238 | −9.212 |
B | 0.86 | 0.232 | 0.241 | −7.812 |
C | 0.99 | 0.178 | 0.182 | −6.739 |
G | 0.83 | 0.208 | 0.210 | −18.488 |
H | 0.87 | 0.211 | 0.212 | −21.818 |
I | 0.86 | 0.200 | 0.200 | −15.976 |
Error analysis of predicted
Face |
|
MAE | RMSE | MAPE |
---|---|---|---|---|
A | 0.95 | 0.223 | 0.228 | −11.369 |
B | 0.92 | 0.196 | 0.197 | −3.718 |
C | 0.95 | 0.198 | 0.198 | −21.524 |
G | 0.95 | 0.096 | 0.099 | −6.717 |
H | 0.96 | 0.094 | 0.128 | −14.053 |
I | 0.89 | 0.195 | 0.197 | −13.872 |
The current study shows that pressure induced on the model building is significantly affected by the model geometry, configuration, aspect ratios, and angle of incidence. The significant outcomes of the present study are summarized as follows: Mean pressure coefficients are the main objective of this study. Maximum positive mean pressure coefficients occur at the front face of C, and maximum negative pressure occurs at the inner face of the model. The study has been conducted with a C-shaped model experimentally as well as numerically using the wind tunnel test and CFD technique, respectively. Pressure variation on the building is directly influenced by wind flow pattern. Vortex generation and different types of mechanism such as separation of flow, upwash, and downwash are happened due to dynamic behavior of wind flow. The predicted values of the error analysis are measured by four accuracy measurement procedures such as
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that they have no conflicts of interest.
The authors express deep sense of gratefulness to Head of the Department of Aerospace Engineering, Indian Institute of Technology Kharagpur, India, for permitting and providing facilities to carry out the experiments. The authors are also thankful to Head of the Department of Civil Engineering, NIT Rourkela, and the National Institute of Technology Rourkela for the support.