Wind–tunnel testing is an integral part of the design process in many industries, typically used to verify and tune the aerodynamic properties of solid objects. Whether an object is stationary or mobile, wind tunnels provide insight into the effects of air as it moves over or around the test model.
To make models for wind–tunnel testing, automotive, aerospace and architectural firms have relied on traditional manufacturing processes including milling, turning and fabrication. Typical materials are metal, plastic and composites. These operations require programming, setup and operator supervision, which adds to lead time and cost.
3D printing (also called additive manufacturing) has rapidly gained acceptance as an alternative process for constructing durable, accurate wind–tunnel test models. Compared with machining and model making, 3D printing with either PolyJet or FDM Technology is faster, less expensive and more efficient.
Additionally, 3D printing can preserve small, inaccessible features that are difficult to make at scale with traditional methods. For example, internal passages are easy to produce, whereas these features would complicate the CNC milling process. 3D printing makes it possible to easily embed equipment into the model, such as pressure-measurement devices and vents for smoke discharge.
PolyJet or FDM is a best fit for wind–tunnel testing when:
- Designs are complex or intricate
- Challenging characteristics include internal cavities, organic shapes or fine feature detail
- Design changes are likely
- Designs are large or bulky
Benefits of PolyJet and FDM models for wind–tunnel testing include:
- Time and cost savings
- The option to embed inserts without drilling
- Availability of lightweight materials
- Ease of creating internal passages for smoke or ink dissipation
- With PolyJet, the option to create transparent models
Application Outline — PolyJet
Producing hollow models is easy with PolyJet technology. This makes the model lighter and reduces material consumption.
Inserts, often stock parts, can reinforce the model if needed, contributing greatly to its dimensional stability. Generally, it’s best to use the largest–diameter rod or thickest plate possible while reaching close to the tip of the model.
The transparent materials available with PolyJet 3D printing can be useful when evaluating the flow characteristics of internal structures. Combining these materials with the complex internal structures that additive manufacturing allows lets designers verify complex internal designs.
Application Outline — FDM
Distinguished by its durable materials, FDM is well suited for constructing wind-tunnel models. Soluble supports allow for complex models with internal cavities to be designed without considering traditional manufacturability. Inserts, including stiffening rods, sensors and fastening devices, can be embedded during 3D printing. The robust thermoplastics used in the FDM process make it possible to assemble the parts to functional assemblies or bond multiple sections together to produce large models. Internal structures can be manipulated to conserve material while maintaining structural integrity.
Customer Story — FDM
Joe Gibbs Racing (JGR), a premier NASCAR race team, regularly tests 40-percent scale models in a full–span, rolling-floor wind tunnel. Test results help improve performance characteristics, such as down force, side force and drag. In the tunnel, JGR simulates the aerodynamic loads on its race cars at conditions equivalent to 200 mph. Mark Bringle at JGR says, “The strength of the materials allows the FDM parts to be tested at high wind speeds without the risk of failure.” According to Bringle, most of these models go into the wind tunnels without any secondary finishing work.
With little direct labor needed and around-the-clock operation, FDM produces models in a few days that would take a week or more to produce with machining or sheet–metal fabrication. In a head–to–head comparison with the sheet-metal fabrication process to create a rear–wheel blower nozzle, JGR found that FDM reduced cost by 89 percent and lead time by 66 percent. The company estimated nine hours of labor to fabricate two halves of the nozzle, weld them together and join them with a machined flange, which would take an additional hour of labor. Conversely, it determined that the FDM process could be completed in three hours with only 30 minutes of direct labor. An added benefit was that the FDM model was significantly more accurate than the sheet metal nozzle (0.005 in. [0.13 mm] versus 0.070 in. [1.8mm]).
How did 3D printing compare with traditional fabrication for Joe Gibbs Racing?
|Traditional Fabrication||$750||3 days|
|SAVINGS||$665 (89%)||55.5 hours (66%)|