# Wind Loads on Overhead Sign Structures: A Comparative Study
## 2 Literature Review  
Most current studies dealing with fluid/air flow experiments can complement their findings using CFD through various software. These flows follow partial differential equations representing conservation laws for mass, momentum, and energy [14]. CFD uses algebraic equations to replace these partial differential equation systems to be solved by a computer. Visual representations such as pressure distributions, velocity vectors, and path lines of airflow are obtained through CFD, giving an insight into flow patterns that are challenging to study using conventional techniques such as wind tunnel testing [15]. The accuracy of the CFD analysis depends on the efficiency of finite element and finite volume methods; in other words, the accuracy and quality of the results depend on the mesh [16]. [PERSON] (2008) studied a sign support structure to calculate the pressure, stress, and bending moments using CFD. The investigations involved simulations under different flow conditions that consisted of steady laminar, transient laminar, and steady turbulent flows at a velocity of 5 m/s. [PERSON] (2008) obtained the bending moment by applying the resulting forces at the center of the horizontal beam of the sign support structure. A comparison of the different flow cases shows that the steady laminar flow drag is higher than its turbulent counterpart. The reason is that, in turbulent flow, all parts of the structure are not under simultaneously uniform pressures (lack of correlation). Additionally, the drag under transient-laminar flow is less than that of steady-laminar flow; the transient flow had a limited time. However, the drag force under the transient-laminar flow would be equal to that of the steady laminar flow if analyzed for an infinite amount of time [11]. An in-depth study considered 16 simulations of single panels of varying sizes: side-by-side signs and back-to-back [17]. Through the simulations, they obtained non-dimensional and dimensional mean pressure differences and the total wind force for each panel. CFD simulations revealed that the characteristics of the flow around the sign panel were relatively the same for all the simulations studied. High pressures on the windward face are due to the decelerating approaching flow. The leeward face shows that the pressure distribution was not uniform, but the pressure levels inside the vorticity region were lower than the ones observed upstream. Pressure values slowly recovered in the vortex region while the streamwise velocity gradually reduced as it continued downstream. The separation of the boundary layer around the panel resulted in amplified turbulent kinetic energy [17]. [PERSON] et al. (2007b) conducted an additional experimental study that put air holes in the sign panel with an aspect ratio of 1:2. The holes' area represented only 2.5% of the total surface area. They generated a high-quality mesh with millions of elements and prism layers and compared the simulation results to those for a solid panel under the same conditions. The results revealed the flow field remained symmetrical, vertically and horizontally, with two large vortices forming on both sides of the symmetry plane. The presence of holes created the formation of two small vortices on the leeward face. The pressure contours show the larger values on the windward face. Behind the panel, the presence of holes increased the mean pressure levels in the vortex region. The lowest pressure levels are observed just behind the openings due to the increased velocity of the airflow coming through these holes. This flow resulted in a smaller force on the panel [17]. When it comes to wind engineering and discussing the airflow around objects, streamlined bodies and bluff bodies are two of the most common examples. These two bodies are classified based on the features of the field they produce when introduced to airflow. A streamlined body, such as an airfoil, is characterized by a thin boundary layer attached to the entire surface, with a narrow and generally steady wake.