Hydrodynamic drag testing was conducted for eleven different configurations of IsoTruss® lattice structures. Flow visualization of prototypical IsoTruss® wind towers was also performed using Particle Image Velocimetry instrumentation. The drag test and flow visualization specimens included 6-node and 8-node configurations, single and double-grid geometries, thick and thin member sizes, smooth and rough surface finishes, a helical-only structure, and a smaller outer diameter test specimen. Three sets of hydrodynamic drag tests were conducted in a closed-circuit water tunnel: 1) orientation drag tests, 2) water velocity drag tests, and 3) height variation drag tests. The orientation drag tests measured the hydrodynamic drag force of the IsoTruss® test specimens at five different orientations with an average water velocity of 1.43 mph (0.64 m/s). The water velocity drag tests measured the maximum drag for each IsoTruss® test specimen at water velocities ranging from 0.0 to an average 1.43 mph (0.64 m/s). Based on the average outer structure diameter of the IsoTruss® specimens, the water velocities corresponded to a Reynolds number range of 7,000 to 80,000. Based on the average member diameter, the corresponding Reynolds number spanned from 600 to 3,000. In addition, the height variation drag tests were performed by vertically extracting the IsoTruss® test specimens from the test section at four different immersed height levels, with a maximum immersed height of 7.22 in (18.1 cm). The height variation testing corresponded to a Froude number range of 0.40 to 0.90. The IsoTruss® specimens exhibited an average lower drag coefficient based on the projected cylindrical area than the smooth circular cylinder data throughout the Reynolds number and Froude number ranges. The drag coefficient based on solid member area showed no correlation when shown as a function of the solidity ratio. However, for the drag coefficient calculated from the solid member projected area, the data for all IsoTruss® test specimens collapsed to a 2nd order polynomial when presented as a function of the Froude number, with an R2 of 0.99. Conversely, no significant relationship was shown when the drag coefficient based on projected cylindrical area was plotted versus the Froude number. The hydrodynamic data was compared to aerodynamic data, and the orientation testing results were identical. The hydrodynamic data differed by an average of 17% compared to the non-dimensional aerodynamic results. The flow visualization research revealed that the velocity returned to 2% of the freestream velocity at 1.24 diameters upstream from the prototypical IsoTruss® wind tower. Likewise, the velocity returned to a maximum 4% of the freestream velocity at 0.94 diameters sidestream of the model IsoTruss® wind tower.



College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering



Date Submitted


Document Type





hydrodynamic drag, solidity ratio, IsoTruss structures, lattice structures, aerodynamic drag, particle image velocimetry, flow visualization, drag coefficient, froude number