THE INFLUENCE OF LENGTH CUTS TRAILING EDGE ON FLOW CHARACTERISTICS IN THE RAILWAY HELM USING COMPUTATIONAL FLUID DYNAMICS

There are many important reviews about the flow characteristics in the body of the racing bike helmet caused by the relative motion of the air along the Trailing Edge shape. The lines formed in such a way in the speed field will form a streamline stream so that the lines are in line with the flow at each point in the flow field. Thus, the streamline will form a pattern of airflow around the helmet. This aerodynamic characteristic study was performed on time meter helmet body visualized numerically using Computational Fluid Dynamics (CFD) with Solid Work Flow Simulation software. With variation of Trailing Edge 25 mm, 75 mm, 125 mm. Urgency research about helm time trial is believed to provide information about the flow that occurred. The result shows that the drag coefficient reduction that occurs on the cut variation of 75 mm compared with other variations on the Reynolds number 1.16 x 105 of 0.395.


Computer Specifications
The thing that needs to be considered in conducting CFD simulations is the computer specifications used.The higher and better the computer specifications used so the time needed for the simulation process.In this study using computer specifications as shown in Table 1 below:

Results of Simulation of Various Model
Variations in Reynolds Numbers 1.00 x two parameters being the foundation for the development of concepts and applications of aerodynamics as well as the field of automotive(Fox et al., 2011).Currently, developing countries in the world much to make the technology grow and modern as in the world of cycling.The technology is widely used for research on aerodynamic flow and drag coefficient on racing bike helmets.Basically the aerodynamic characteristics that occur in the body of the bicycle racing helmet is caused by the relative movement of the air along the shape of the body helmet.The lines formed in such a way in the speed field will form a streamline so that the lines will be in the direction of the flow at each point in the flow field.Thus, the streamline will form a pattern of airflow around the helmet.Performance for racing bikes is intended to reduce the frontal area when the athlete's head is exposed to flow throughout the body that can significantly improve performance.Aerodynamic improvements apply aerofoil shapes with Trailing Edge modifications to the design of the helmet.One of the goals for knowing performance with cutting variations on Trailing Edge is to reduce the desired aerodynamic drag.A study conducted by Bradford and Peter (2011) on Trailing Edge cut variations on racing helmets indicates different cutting lengths of 0.5 m and 0.85 m resulting in the lowest drag coefficient.The length of the helmet affects the size and formation of the vortex.The helmet geometry at the intersection of about 0.5 m and 0.85 m forms a small vortex on the Trailing Edge.The optimal length to reduce the drag coefficient is obtained at a 0.5 m intersection.This length has a slightly higher drag coefficient but will present a reduced frontal area if the helmet is rotated 90 degrees into the airflow.In contrast to Bradford and Peter, the initial research conducted by Nash et al (1966) focused on the low pressure zone formed behind the trailing edge.This modified rear area of the body leads to increased pressure and substrate bottlenecks for splitter plates, wedges, cavities and other methods to reduce basic obstacles.An airfoil with a dull end is observed and produces the most effective characteristic with a rounded versus square trailing edge.Chabroux et al (2008) also studied the effects of ventilation on the drag force using three similar aerodynamic helmets.One helmet has open ventilation, one having a small vertical slit opening, and the other one has no ventilation.Their data showed no significant difference in the drag force between the three helmets.Van Dam, Kahn, and Berg (2008) saw the application of cut airfoils to the inboard region of wind turbine blades.The clipped form provides improved lift and better Vol.3, No.1, July 2018 ISSN 2528-2611, e-ISSN 2528-2700 structural characteristics but also shows a significant increase in drag compared to airfoils with sharp trailing edges.While in this study wanted to show the characteristics of aerodynamics performed on the body helm time trial by numerical visualization using CFD software with cut variations of Trailing Edge 25 mm, 75 mm, 125 mm.Urgency research about helm time trial is believed to provide information about the flow that occurred.METHODOLOGY This research was carried out by first describing the design in solidWorks Flow Simulation software.The geometry scheme can be seen in the figure below.

Figure 1 .
Figure 1.Cut Variations in trailing edge The pre-processing stage is the initial stage to analyze CFD modeling.This stage consists of making geometry using CFD software in pre-processing, among others as follows: 1. Making geometry models in the process of analyzing the flow characteristics, geometry models are made in advance with several stages: a.First determine the plane we will use to draw the geometry, here the author uses the top plane to start drawing.b.After determining the plane, based on the previous study which discussed the time-trial helmet, by Bradford W Sims, Peter E Jenkins (2011), the geometric shape planning was obtained which would later be used as a reference for taking points of plot coordinates x, y for the next point Vol.3, No.1, July 2018 ISSN 2528-2611, e-ISSN 2528-2700 are connected to a 2D model build.The following is a picture of a previous study by Bradford W Sims, Peter E Jenkins (2011) which will be used as a reference for taking points of plot coordinates x, y.

Figure 2 .
Figure 2. 2D model of time-trial helmet from a previous study by Bradford W Sims, Peter E Jenkins (2011) Based on the image above will be taken points on the software CFD, so that the geometry of time-trial helmet coordinates for the present study will be formed as shown in Figure 3 below.

Figure 3 .Figure 4 .Figure 5 .
Figure 3. Results of point coordinates in CFD software Figure 3, it is known the position of each point that has been adapted to the shape and dimensions of the Bradford W Sims

Figure 7
Figure 7 (a) is the flow visualization of the fluid flow across the helmet 2D time trial is shown above at Reynolds number 1.00 x 10 5 .In the figure shows the fluid flow trace when crossing the helmet body and it is seen that the flow will follow the body contour.But when the fluid will cross the

Figure 6 .
Figure 6.Flow visualization figure at Reynolds number 1.00 x 105 (a) Bradford W Sims, Peter E Jenkins (2011) (b) Results of the present study.

Figure 7 Figure 7 .
Figure 7 (c) for Reynolds number 1.00 x 10 5 with modification of Trailing Edge pieces as long as 75 mm, Flow Visualization of fluid flow across the 2D time-trial helmet appears above.for flow patterns on variations of 75 mm cut that are shown above the image turns away because