Computational Fluid Dynamics for Biomimetics

THE CANADIAN SCIENCE FAIR JOURNAL ARTICLE Computational Fluid Dynamics For Biomimetics: Springtails Are Not a Drag! Harini Karthik Age: 16 | Montreal, Quebec Online STEM Fair Regionals Ribbon (2020) | Youth Science Canada Ribbon (2020) Drag is a true annoyance for many industrial sectors around the world. Drag force is produced by the friction of a flowing fluid flowing on the surface that lowers the energy efficiency of the system. This experiment attempts to minimize the drag force by testing theoretical biomimetic coatings. This approach was proven efficient using the digital method known as Computational Fluid Dynamics (CFD) for solving this fluid-flow problem. The morphological structures of different organisms were modeled using software tools such as Salome, OpenFOAM, and ParaView for further comparison. According to the results generated by the simulations, the drag reduced significantly for moderate Reynolds’ Number ranges. This technique can be applied to fabricate hydrophobic coatings to maximize the energy efficiency of various systems like solar panels. INTRODUCTION Drag is an invisible resistive force that challenges the performance of various industrial sectors. In the scientific world, drag measures the system’s energy efficiency in reference to the surface topography and the rate of the flowing fluid. Flat surfaces are observed to cause flow instabilities, thereby increasing the friction (drag). The morphological structures of biological organisms (Tetrodontophora Bielanensis, Rosaceae, and Morpho Peleides) were modeled using software tools such as Salome, OpenFOAM, and ParaView. Computational Fluid Dynamics (CFD) was a digital method that was applied to solve this fluid-flow problem. Results indicated that streamlined surfaces are better at vortex shedding compared to planar surfaces. Vortex shedding avoids producing flow instabilities by creating a lower pressure region for more energy. By varying the velocity of the upcoming fluid and patterns of the morphological structures, the drag force reduced significantly (NASA HYPOTHESIS Glenn Research Center, 2015). Comparatively, researchers have If a fluid flows over a surface which exhibits a lot of vortex shed- altered the geometric models in macroscopic applications such as ding, the drag will be reduced, as compared to a planar surface. automobiles, planes, and swimsuits. By modifying the surface to- This was assumed by nature of vortex shedding process that prop- pography on a microscopic scale, drag reduction will prevent the agates the pressure of upcoming fluid at a direction perpendicular adhesion of fluid-like particles on the surface. This biomimetic ap- to the fluid flow (Fu, 2018). proach is environmentally-friendly, efficient, biodegradable, and METHODOLOGY copiously available. Salome, OpenFOAM and Paraview were used to analyze the PURPOSE identified specimen through geometric, mathematical, and visual This experimentation focuses on adopting nature’s microscopic de- modelling. For the purpose of experimentation, CFD’s fluid-flow formities as a surface coating to reduce drag (Fig.1.1). Theoretical package was utilized to generate external factors that influence biomimetic coatings were assessed based on their geometries in drag, while the pressure was kept constant and numerical solu- reference to the performance of flat surface. tions are driven through the Finite Volume Method (Wolfram MathWorld, 2001). This method discretized the mesh to solve the fluid-flow equations. Exterior factors such as freestream velocity of fluid and morphological geometry will only affect the results, This work is licensed under: whereas the pressure of the fluid remained the same as it is in- https://creativecommons.org/licenses/by/4.0 CSFJ | Volume 3 | Issue 4 © Karthik 2020 1 THE CANADIAN SCIENCE FAIR JOURNAL ARTICLE STAGE 3: POST-PROCESSING compressible. Flat surface was a constant model in this experi- In ParaView, the results for pressure, velocity, and vorticity were mentation to compare the overall reduction with the methods that viewed in a cross-sectional perspective that is perpendicular to the are used today. The temperature remained constant throughout direction of fluid-flow. This tool enabled the usage of stream-trac- the simulation. The governing equations of incompressible fluids ers to present the velocity field aesthetically. The post-processing are Navier-Stokes Equations in which the conservation of mass file contained the data for drag coefficients. states that the mass increase is equal to the total inflow of mass RESULTS (Tryggvason,G., 2011). This concept applies to the inflow of fluid coming at a higher velocity and passes by the microstructure to create a higher drag. STAGE 1-PRE-PROCESSING The geometries of identified morphological structures were con- structed in Salome. The cross-sections of morphological structures were traced on a coordinate plane and the points were cop- ied to Salome to create a two-dimensional outline. A revolution around 360 degrees was applied for curved models such as Rosa- ceae and Tetrodontophora Bielanensis. The outline was extruded along the z-axis to create deep tunnels for the Morpho Peleides model. A bounding box was installed around the geometry to lo- cate the simulation (Pluralsight, 2014). The mesh used was tetra- hedrons generated using Netgen 1D-2D-3D algorithm. STAGE 2: SOLVER In OpenFOAM, the standard configuration of fluid properties in- cluded viscous, incompressible, laminar, and Newtonian. These characteristics were chosen for this assessment and the calcula- tions were measured down to micrometers. The fluid flowed in a horizontal (+x) direction from inlet to outlet. The drag reduction was monitored by varying the freestream velocity between 0.001 to 1 m/s and designs of geometric bodies. The boundary conditions were defined in all regions of the solid to connect the geometric model with the environment. The velocity and pressure values were kept constant at multiple solid faces (SimScale, 2020). No slip and zero gradient conditions were applied at the walls which include the peak and bottom. After setting up the files, the simulation was executed in which iterations through timesteps generated solutions (Fig.2.3). The final solution is when the velocity profile stops changing for this steady-state fluid-flow. CSFJ | Volume 3 | Issue 4 © Karthik 2020 2 THE CANADIAN SCIENCE FAIR JOURNAL ARTICLE 1-Tetrodontophora Bielanensis data of drag coefficients resulted from the mesh variation and the According to the data provided in table 3.1, Tetrodontophora Biel- bending point was created by the curved structure difference as anensis had the lowest drag coefficient of 98.4. In comparison with to a linear plane calculation. The external factors that were set the flat surface (control model) which amounted to 593, the drag before modelling resulted in internal results that showed diversity coefficient was reduced by 83% for a freestream velocity of 1 m/s in pressure, velocity, and vorticity in the region. Standard fluid (Fig.3.2). The Reynolds Number remained small for all the geome- properties of incompressible water were used as a test incoming tries to maintain a laminar flow and predict future results according fluid to lessen the impact of adhesion on the surface. The bound- to the pattern (Fig.3.3). There was a steady fluid flow that avoided ary conditions of certain geometric faces set to zero velocity and the waste of energy. The amount of vortices formed near the struc- pressure was justified by lessening the boundary layers, maintain- ture lowered leading to a smaller drag coefficient. ing a laminar flow, and lowering pressure near morphology. Higher pressure, increasing vortices, and low velocity near 2- Rosaceae Other surface topographies such as Rosaceae have the second the curve contributed to maximize the drag. This factors are det- smallest drag coefficient of 250. The parabolic shape of Tetrodon- rimental to the vortex shedding of the geometry by concentrating tophora Bielanensis and Rosaceae reduce drag force significantly the vortices closer to the curve. Therefore, the prediction that because they lower the amount of pressure in front of the surface. lower freestream velocity will create a smaller drag was proven This results in less energy dissipation. They possess more surface wrong as they tend to form boundary layers to have a negative curves that eliminate flow separation and thin the boundary lay- influence on drag. Moderate freestream velocity decreased the er for a lower pressure drag (Aerospace engineering blog, 2018). friction applied on the morphological structure and results in a Their rough surface topography and high freestream velocity re- low Reynolds’ Number for minimized drag. duced skin-friction drag. The Reynolds Number is calculated using FUTURE IMPROVEMENTS the freestream velocity, characteristic length, fluid density, and dy- I would like to improve my project by testing the drag reduction namic viscosity of fluid. Rosaceae had the second smallest Reyn- for the entire topography instead of a single prototype. Nano-scale olds Number of 155 for a freestream velocity of 1 m/s which indi- grooves and layering could be added to the micro-scale morpho- cates that it has thinner boundary layer compared to other models. logical structure to generate solutions mimicked from real-life This will result in a pressure of 5 m2/s2 closer to the curve as the structures. I would like to extend the research on various physical fluid flows at a speed of 1 m/s. conditions. 3-Morpho Peleides REAL-WORLD APPLICATIONS On the other hand, Morpho Peleides structure has a higher drag This biomimetic approach used in this computational sciences re- coefficient of 285 because of its sharp edges and flat rectangular search supports that planar surfaces are detrimental to the drag bars that create vortices. The morphological structure of Rosaceae coefficients. Since water’s kinematic viscosity was programmed has a closer drag force compared to Morpho Peleides because they in the simulation, hydrophobic surfaces could be fabricated to re- possess smoother surfaces that contribute to more vortices for a pel the flow of water molecules. For instance, the hydrophobic higher drag.

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