SummaryExtensive research has been previously conducted on pressure distribution of cylindrical models under uniform and laminar flow conditions. However, typical civil structures such as high-rise buildings or towers are under the atmospheric boundary layer (ABL) conditions. Knowing this, the present research aims to quantify the effectiveness of surface patterns in reducing the suction zone under a simulated ABL condition. Two different surface patterns, U-grooved and V-grooved, were selected to be tested in wind tunnel. In addition to patterned cylinders, tests were also conducted on a smooth-surfaced cylinder, serving as the control of the experiment. An array of roughness elements was placed at the upstream end of the test section with the purpose of inducing ABL winds within the test section. Without the ABL wind, the cylinder covered in V-grooved riblets was most effective in reducing the suction zone followed by the U-grooved cylinder. With the simulated ABL condition, V-grooved cylinder continued to show decreased suction although the amount of decrease was less. Both grooved cylinders showed decreased peak pressure coefficients under the ABL condition compared to the non-ABL condition.KEYWORDS atmospheric boundary layer, cylinder, flow separation, pressure coefficient, surface pattern, wind tunnel 1 | INTRODUCTION High-rise buildings, categorized as any structure requiring the use of a mechanical vertical transportation system (i.e., elevators), can vary greatly in size, from a common 10-story office building to the 828-m-tall Burj Khalifa in Dubai. Although each structure faces its own design challenges, wind is a major determining factor in high-rise buildings.As wind strikes a structure, flow may remain attached or be separated from the surface of the structure. The windward side experiences a positive pressure whereas the leeward side experiences a negative pressure, often referred to as suction. [1] Flow separation typically causes an increase in pressure drag that is the form of drag caused by the pressure differences between the front (windward) and rear (leeward) surface of a structure. By delaying the separation point (occurring at a leeward point), pressure drag can be reduced.All experiments related to delaying the flow separation can be grouped into 2 major categories, passive or active. A passive mechanism is one that is related to the building architecture, where features are intentionally incorporated into a design in order to dictate fluid flow around a particular surface. Oppositely, an active mechanism requires that external energy be added into a particular system. [2] The current paper will deal strictly with passive mechanisms.The majority of techniques researched with cylindrical structures involves surface manipulation, such as added roughness or patterns. The following ideas have been previously tested: grooves, [3][4][5] bumps and dimples, [6][7][8] and screens, [9,10] among others. These studies showed that surface manipulation can effectively delay the separation point. Delay...