After identifying the ecological and economic drivers for use of laminar flow technology, we outline the mechanisms of laminarturbulent boundary layer transition and review the status of natural laminar flow (NLF) and hybrid laminar flow control (HLFC). New ways to reduce the complexity of HLFC systems are presented, and the remaining steps to achieve technology readiness are discussed.

287In this paper continuation methods are applied to the axisymmetric Navier-Stokes equations in order to investigate how the stability of spherical Couette flow depends on the gap size 0'. We find that the flow loses its stability due to symmetry-breaking bifurcations and exhibits a transition with hysteresis into a flow with one pair of Taylor vortices if the gap size is sufficiently small, i.e. if u ~ uB.In wider gaps, i.e. for CTB < u ~ CTF, both flows, the spherical Couette flow and the flow with one pair of Taylor vortices, are stable. We predict that the latter exists in much wider gaps than previous experiments and calculations showed. Taylor vortices do not exist if u > CTF. The numbers CTB and uF are computed by calculating the instability region of the spherical Couette flow and the region of existence of the flow with one pair of Taylor vortices. IntroductionWe consider a flow of a viscous incompressible fluid contained between two concentric spheres. The outer sphere is fixed while the inner one rotates. If the inner sphere rotates slowly the flow contains two large cells ranging from each pole to the equator. This flow is uniquely determined by the Reynolds number, and is called 'spherical Couette flow' ( cf. figure 1). By increasing the Reynolds number, Khlebutin to produce the Taylor-vortex flow by rotating both spheres and stopping the outer one when the vortices appeared. They observed a transition back into spherical Couette flow if the Reynolds number was decreased. However, the Taylor-vortex flow cannot be produced by rotating only the inner sphere. In that case, the spherical Couette flow remains stable until it encounters the so-called 'wide-gap instability'

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A flight test with a simplified HLFC system on the vertical tail plane of an A320 aircraft was performed in April/May 2018. The aerodynamic and system design is discussed and first results of the flight tests are presented. Subscripts: q c = Subscript 'c' denotes a quantity in a suction chamber q d = Subscript 'd' denotes a quantity in the plenum or duct q s = Subscript 's' denotes a quantity on the outer side of the microperforation q 0 = Subscript '0' denotes a reference quantity q ∞ = Subscript '∞' denotes a quantity in the oncoming freestream

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Within the European Project Telfona the Pathfinder Model was designed, analyzed numerically, constructed and tested with the aim of obtaining a laminar flow testing capability in the European Transonic Wind Tunnel (ETW). The model was designed for natural laminar flow (NLF) for transonic flow conditions with high Reynolds number.Results of pre-test numerical analysis demonstrated that the Pathfinder wing pressure distribution was adequate for providing calibration test points. The ETW tests provided pressure distribution data while transition positions were determined from images using the Cryogenic Temperature Sensitive Paint Method (cryoTSP). The evaluation of this data with several transition prediction tools was used to establish the transition N-factor values for ETW. In this work, after-test CFD solutions are obtained using numerical Navier-Stokes solutions. In the first part of this work, numerical results are given which verify the requirements of the Pathfinder wing as a calibration model. In the second part, it is shown that for selected flow conditions a good agreement is obtained between stability analysis based on experimental and numerical data. In the third part the correlation of experimental transition locations to critical N-factors is summarized for ETW Test Phases I and II. In the fourth part numerical analysis and experimental data are used complementarily.

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