Flight experiments carried out with a motorized glider yield insights into the aerodynamic processes acting on a laminar wing section under varying on-coming flow conditions. Measurement data are obtained on a laminar wing glove equipped with pressure transducers and wall microphones to detect transition and investigate the boundarylayer instabilities. The on-coming flow, including the instantaneous angle of attack and the turbulence characteristics, is measured with hot-wire sensors. The flight tests were carried out under calm and moderately turbulent conditions. Characteristic results for both on-coming flow conditions are presented and differences are analyzed. Selected comparisons of the experimental results with steady boundary-layer and linear stability computations are provided. The effects observed in the experiments cannot be described solely by quasi-steady theory. Unsteady changes of the pressure distribution are identified as one source for the modification of the transition development. A conclusion on the observed superimposed effect of increased levels of atmospheric small-scale turbulence on boundary-layer receptivity cannot yet be drawn from the present experiments.
Nomenclature= turbulent kinetic energy density spectrum, m∕s 2 ∕m −1 E xx = one-dimensional energy density spectrum, m∕s 2 ∕m −1 F = dimensionless stream function, -k = wave number, 1∕m k x = streamwise wave number, -k z = spanwise wave number, -L I = integral length scale, m L ref = reference length, m l k = Kolmogorov length scale, m m = dimensionless pressure gradient, -N = N factor, -P = pressure, Pa P = mean pressure, Pa p 0 = pressure fluctuation, Pa q 0 = dimensionless disturbance vector, -q = dimensionless disturbance amplitude function, -Re = Reynolds number, -Tu xy = two-component turbulence intensity, -U = velocity vector U; V; W T , m∕s U = mean velocity vector U; V; W T , m∕s U e = edge velocity, m∕s U eff = effective velocity, m∕s U ref = reference velocity, m∕s U TAS = true airspeed (U ∞ ), m∕s U ∞ = freestream velocity, m∕s u 0 = fluctuation velocity vector u 0 ; v 0 ; w 0 T , m∕s x = streamwise coordinate, m y = wall-normal coordinate, m z = spanwise coordinate, m α = angle of attack, deg β = sideslip angle, deg ε = energy dissipation rate, m 2 ∕s 3 η = dimensionless Falkner-Skan variable, -θ = probe axis inclination to the flow, deg ν = kinematic viscosity, m 2 ∕s ρ = air density, kg∕m 3 Ψ = stream function, m 2 ∕s ψ = yaw angle, deg ψ = wire slant angle for θ equal to zero, deg ψ eff = effective yaw angle, deg ω = angular frequency, 1∕s
