Laminar Flow Control on a Swept Wing with Distributed Roughness

Roughness Based Crossflow Transition Control: A Computational Assessment

“…parallel to the leading edge) as a fraction of the freestream velocity. The combined evolution of the control and target modes with the initial amplitude of the 4.5 mm mode held fixed at 4 10 − (based on the preceding discussion for the 5 mm mode) is shown in Fig. 3(a).…”

“…Spanwise variations in the computed pressure distribution over the mid-span segment of the suction surface were relatively small, so that the region in between the rows of static pressure ports at 13 inch and 29 inch span locations outboard of the mounting plane approximated (locally) infinite span conditions. Transition measurements, both without and with the use of DRE, were reported in [4].…”

“…Flight observations under somewhat different conditions (Re c = 8.1x10 6 and AOA = -4 deg) [4] had shown that, with a painted leading edge (average roughness height of 1.0 µm rms and 3.8 µm average peak-to-peak), the natural onset of transition at the spanwise section of interest was near x/c ≈ 0.3, whereas transition was delayed beyond x/c ≈ 0.8 when the leading edge surface was unpainted and, therefore, was considerably smoother (r.m.s. roughness height of 0.3 µm rms and 2.2 µm average peak-to-peak).…”

“…The flow configuration examined herein corresponds to the SWIFT flight test article from [4]. A 30-degree swept airfoil was mounted vertically beneath the wing of a Cessna O-2A Skymaster aircraft and flown at chord Reynolds numbers of 7 to 8 million, in order to investigate the feasibility of DRE technology for SensorCraft applications.…”

“…One of those concepts involves the delay of crossflow-induced transition over a swept aerodynamic surface using control input in the form of appropriately positioned Discrete Roughness Elements (DREs) near the leading edge [3]. A bulk of the existing experimental and computational studies of the DRE concept have been carried out for either incompressible or supersonic configurations with modest wing-chord Reynolds numbers of up to approximately 8 million [4,5], and with pressure distributions that may or may not be optimal for wing designs for subsonic transport aircraft flying at Mach numbers between 0.75 to 0.90. Consequently, additional effort will be necessary to assess the potential capability of the DRE concept to control swept wing transition at transonic Mach numbers and substantially higher chord Reynolds numbers than previous applications.…”