Transition Delay with Cylindrical Roughness Elements in a Laminar Water Channel

Transition delay using biomimetic fish scale arrays

“…To prove their existence also on the real fish skin, oil flow visualisation was done on sea bass and common carp, which indeed confirmed their presence in a regular manner along their real body, with the same arrangement relative to the scale array as observed along the biomimetic surface. These results let the authors hypothesize about a possible mechanism for transition delay, inspired by various previous fundamental transition studies, where streaky structures generated by cylindrical roughness elements or vortex generator arrays have shown a delay of transition [18][19][20] .…”

“…The experiments were conducted in the Laminar Water Channel of the Institute of Aerodynamics and Gas Dynamics in Stuttgart, Germany. The test section dimensions are 10 m in length (streamwise direction: X -axis), 1.2 m in width (spanwise direction: Z -axis) and 0.2 m in height (wall-normal direction: Y -axis) with a turbulence intensity value less than 0.05% 20 . Hot-film anemometry was used to measure the velocity of the flow inside the water channel.…”

“…Location of the wire within the boundary layer and the vibration frequency are adapted to the theoretical instability diagram of the Blasius solution for a laminar 2D boundary layer 27 . A wire of 0.1 mm diameter is located at from the leading edge of the flat plate 20 at a wall-normal distance of 5 mm from its surface and vibrating at a physical frequency of (the corresponding normalised frequency is ) with an amplitude of 0.25 mm.

Figure 3 Comparison of CFD with experimental results ( A ) Velocity variation of streaky base flow in plane at a distance of 1.2 m from the leading edge (Left—CFD result, Middle—Hot-film result, Right—Blasius).

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Transition Delay Using Biomimetic Fish Scale Arrays

“…To prove their existence also on the real fish skin, oil flow visualisation was done on sea bass and common carp, which indeed confirmed their presence in a regular manner along their real body, with the same arrangement relative to the scale array as observed along the biomimetic surface. These results let the authors hypothesize about a possible mechanism for transition delay, inspired by various previous fundamental transition studies, where streaky structures generated by cylindrical roughness elements or vortex generator arrays have shown a delay of transition 18,19,20 . The main purpose of this study is to prove this hypothesis with experiments in a well-established low-turbulence water channel facility, where the transition process can be studied under well-defined boundary conditions with controlled excitation of the fundamental instability of the Tollmien Schlichting waves.…”

“…The experiments were conducted in the Laminar Water Channel of the Institute of Aerodynamics and Gas Dynamics in Stuttgart, Germany. The test section dimensions are 10m in length (streamwise direction: X-axis), 1.2m in width (spanwise direction: Z-axis) and 0.2m in height (wall-normal direction: Y -axis) with a turbulence intensity value less than 0.05% 20 . Hot-film anemometry was used to measure the velocity of the flow inside the water channel.…”