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DMR effect on drag reduction of a streamlined body measured by Magnetic Suspension and Balance System

Aiko Yakeno, Hiroyuki Okuizumi, Kento Inokuma, Yoshiyuki Watanabe

Abstract

This study experimentally investigates the aerodynamic drag reduction capabilities of distributed micro-roughness (DMR) coatings on a streamlined model, utilising the 1-m magnetic suspension and balance system (MSBS) at Tohoku University. Previous direct numerical simulations (DNS) indicated that DMR can mitigate turbulent-energy growth by suppressing Tollmien--Schlichting (TS) waves and influencing the breakdown of streamwise vortices. The present work provides the first experimental validation of these effects using an interference-free MSBS, which is essential for accurate measurement in the laminar and transitional regimes. A streamlined model was tested with two rows of artificial tripping tape to induce transition; the DMR height was approximately 1% of the local boundary layer thickness, significantly smaller than typical roughness elements. Direct aerodynamic drag measurements using the MSBS revealed a substantial reduction of up to 43.6% within the transitional flow regime. Crucially, integrated analysis using wall-resolved large-eddy simulations (LES) and dynamic oil-flow visualisation confirmed that this benefit does not mainly originate from the suppression of flow separation. The LES drag decomposition established that the total pressure-drag budget is subordinate to skin friction, a finding complemented by oil-flow observations, which revealed qualitatively similar flow patterns regardless of the surface condition. Consequently, the observed drag reduction is primarily ascribed to friction drag reduction achieved through the modification of the boundary layer state. These findings provide compelling experimental evidence for the efficacy of DMR and offer valuable insights for optimising surface designs for passive flow control.

DMR effect on drag reduction of a streamlined body measured by Magnetic Suspension and Balance System

Abstract

This study experimentally investigates the aerodynamic drag reduction capabilities of distributed micro-roughness (DMR) coatings on a streamlined model, utilising the 1-m magnetic suspension and balance system (MSBS) at Tohoku University. Previous direct numerical simulations (DNS) indicated that DMR can mitigate turbulent-energy growth by suppressing Tollmien--Schlichting (TS) waves and influencing the breakdown of streamwise vortices. The present work provides the first experimental validation of these effects using an interference-free MSBS, which is essential for accurate measurement in the laminar and transitional regimes. A streamlined model was tested with two rows of artificial tripping tape to induce transition; the DMR height was approximately 1% of the local boundary layer thickness, significantly smaller than typical roughness elements. Direct aerodynamic drag measurements using the MSBS revealed a substantial reduction of up to 43.6% within the transitional flow regime. Crucially, integrated analysis using wall-resolved large-eddy simulations (LES) and dynamic oil-flow visualisation confirmed that this benefit does not mainly originate from the suppression of flow separation. The LES drag decomposition established that the total pressure-drag budget is subordinate to skin friction, a finding complemented by oil-flow observations, which revealed qualitatively similar flow patterns regardless of the surface condition. Consequently, the observed drag reduction is primarily ascribed to friction drag reduction achieved through the modification of the boundary layer state. These findings provide compelling experimental evidence for the efficacy of DMR and offer valuable insights for optimising surface designs for passive flow control.
Paper Structure (21 sections, 21 figures, 5 tables)

This paper contains 21 sections, 21 figures, 5 tables.

Table of Contents

  1. Background
  2. Method
  3. Wind Tunnel Facility
  4. 1-m Magnetic Suspension and Balance System (1-m MSBS)
  5. Test Model Description
  6. DMR Coating
  7. Phase I
  8. Phase II
  9. Computational Methodology: Large Eddy Simulation (LES)
  10. Validation of Measurements
  11. Measurement Error
  12. Stability of the Model Position and Attitude
  13. Comparison of LES Results with Experimental Results without Tripping (Phase I)
  14. Results and Consideration
  15. Results for Cases with Tripping Tape 1 (Phase I)
  16. ...and 6 more sections

Figures (21)

  • Figure 1: The streamlined model in 1-m Magnetic Suspension and Balance System (1-m MSBS) installed in the low-turbulence wind tunnel. The system uses electromagnetic forces to suspend the test model without physical supports, allowing for highly accurate, interference-free aerodynamic measurements.
  • Figure 2: A photograph of the streamlined test model.
  • Figure 3: Geometry of parts of the streamlined test model.
  • Figure 4: Colouring of the streamlined test model as a side view cross-section.
  • Figure 5: Trip tapes.
  • ...and 16 more figures