Assessing Aerodynamic Performance by Exploring the Role of Trip Wires with the Latest Release of Ansys Discovery and Its New Capabilities.
Challenges
Aerodynamics is the study of how gases, particularly air, interact with solid objects in motion. It plays a critical role in various engineering fields, influencing the design and performance of vehicles, buildings, and industrial systems. One of the key forces in aerodynamics is drag, the resistance experienced by an object moving through a fluid. Drag force arises from friction and pressure differences around an object, directly affecting its speed, efficiency, and energy consumption. In many industries, minimizing drag is essential for improving performance and reducing operational costs. Sectors that benefit from low drag include:
- Automotive. Electric vehicles, high-performance sports cars.
- Aerospace. Aircraft, drones.
- Renewable energy. Wind turbine blades, solar panel aerodynamics.
- Marine engineering. Ships, submarines.
To reduce drag, engineers use flow control techniques [1] such as streamlining shapes, adding vortex generators, using riblets, and applying boundary layer suction. Another effective method is the trip wire, a small protrusion placed on a surface to trigger early transition from laminar to turbulent flow. While turbulence typically increases drag, a well-positioned trip wire can help delay flow separation, reducing pressure drag on bluff bodies like spheres, cylinders, and airfoils.
Engineering Solutions
Engineers have studied the effects of trip wires using analytical, experimental, and numerical techniques to understand their impact on flow behavior and drag reduction.
- Analytical models rely on boundary layer theory and empirical correlations to predict how trip wires influence transition from laminar to turbulent flow. These models help estimate critical Reynolds numbers and the resulting changes in drag and pressure distribution. While analytical methods provide valuable initial insights, their accuracy is limited for complex geometries and flow conditions.
- To validate and refine these models, researchers conduct experimental studies using wind tunnels, water channels, and pressure sensors to measure flow characteristics around trip wires. Techniques such as particle image velocimetry (PIV) and hot-wire anemometry allow for detailed visualization and quantification of velocity fields and turbulence.
- Complementing these experiments, numerical simulations using Computational Fluid Dynamics (CFD) provide deeper insights by solving the Navier-Stokes equations for various trip wire configurations. CFD studies help engineers analyze different trip wire sizes, placements, and operating conditions, enabling optimized designs for applications in aerospace, automotive, and industrial systems.
Ansys present a series of validated cases for Discovery 2025 R1 that can be found in the Help Manual. One of them is the Ahmed body drag coefficient simulation. The picture below shows the results using the Explore mode with good results. In the next section, another application of external aerodynamics flows is presented using the 2025 R1.
Methods
Case Study: Trip Wire Effects on a Sphere
Part of the experiment conducted by Son et al in 2011 [2] has been replicated numerically in Ansys Discovery. Usually, the Refine mode is recommended for more accurate results, but in this Demo the results are obtained in the Explore mode to show a new capability of the 2025 R1 release. This capability refers to the enhanced force monitors, which now include viscous shear force in addition to pressure force, which is the nature of the drag force (See Chapter 7 in [3]). Therefore, the drag coefficient (CD) is given by:
Some of the geometry details are mentioned as follows:
- Sphere Diameter, D = 150 mm
- Trip wire Diameter and location, d = 2 mm & q = 50° from the stagnation point
- Wind tunnel, cross section area (L1): 600 mm x 600 mm (Blockage ratio: 4.9%)
- Fluid: Air (Density = 1.16 kg/m3, Viscosity = 1.832x10-5 Pa.s)
- Reynolds Number, Re = 5x104 (velocity = 5.24 m/s)
The mesh can be visualized during the solution process in Explore Mode, either in 3D view or through cutting planes. By default, the mesh includes refinement at the inlet and outlet sections to improve accuracy. To ensure precise results, surface refinement is applied, with a local fidelity of 0.4 mm on the sphere surface and 0.1 mm on the trip wire. The simulations are performed using an NVIDIA T1000 8GB GPU working at top capacity.
Results
The picture below compares the flow over the sphere with and without the trip wire. As expected, the trip wire delays flow separation, reducing the low-pressure wake and thereby decreasing pressure drag. The drag coefficient determined from the experiments (see Fig.4 in [1]) for d/D = 1.33x10-2 and Re = 5x104 is 0.42. The validation is achieved based on the Drag force calculation. The value reported by the monitor in the Explore Mode is 0.118 N. Then, by using this result, the numerical drag coefficient is calculated as follows:
Ansys Solution Benefits
Ansys Discovery is an interactive simulation tool that integrates 3D modeling, design, and real-time analysis to streamline engineering workflows. It combines direct modeling technology with instant physics simulation, enabling users to modify designs, optimize topology, and explore multiple variations efficiently. Supporting structural, fluid, thermal, and electromagnetic simulations, it provides rapid insights for data-driven decisions.
The platform operates in three stages: Model for intuitive geometry creation, Explore for real-time analysis and quick iterations, and Refine for high-fidelity simulations using Ansys Fluent and Mechanical. Designed for efficiency and innovation, Ansys Discovery helps engineers tackle complex challenges and enhance design performance. Some top capabilities are listed below:
- Parametric Studies. Parameter sweeps enable engineers to evaluate multiple design options simultaneously, revealing trade-offs between different configurations. By analyzing how geometry or physics variations impact results, designs can be optimized for the best solution. In Ansys Discovery, this process is automated, allowing efficient modification of geometric and simulation parameters.
- Optimization. Whether you're accelerating design exploration with cloud-connected burst compute or optimizing designs seamlessly with optiSLang, these latest enhancements make engineering workflows faster and more intuitive than ever. Visit the dedicated website for more information about these topics.
Ozen Engineering Expertise
Ozen Engineering Inc. leverages its extensive consulting expertise in CFD, FEA, optics, photonics, and electromagnetic simulations to achieve exceptional results across various engineering projects, addressing complex challenges like multiphase flows, erosion modeling, and channel flows using Ansys software.
We offer support, mentoring, and consulting services to enhance the performance and reliability of your systems. Trust our proven track record to accelerate projects, optimize performance, and deliver high-quality, cost-effective results for both new and existing water control systems. For more information, please visit https://ozeninc.com.
References
[1] Wang, J. & Feng, L. (2018) Flow control techniques. Cambridge University Press.
[2] Son, K., Choi, J., Jeon, W.P. & Choi, H. (2011) Mechanism os drag reduction by a surface trip wire on a sphere. J. Fluid Mech (Cambridge University Press), Vol. 672, 411-427.
[3] White, F. (2011). Fluid Mechanics. McGraw-Hill series in Mechanical Engineering, 7th Edition.
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