The background-oriented schlieren technique was used to visualize the blade-tip vortices of a Eurocopter AS532UL Cougar helicopter in maneuvering flight. The test program covered a large part of the flight envelope, including maneuvers such as hover flight, fast forward flight, flare maneuvers, and high-speed turns. For selected flight conditions, the aerodynamic results are presented here. It is shown that, with the reference-free background-oriented schlieren method, the detection of vortex filaments up to vortex ages of ψ v 540 deg is possible. The visualization of the vortex system is used to detect aerodynamic phenomena such as blade-vortex interactions, vortex-airframe interactions, and the occurrence of smooth sinuous disturbances. A detailed description of the applied reference-free background-oriented schlieren setup is given, and the suitability of different natural backgrounds for the background-oriented schlieren method is analyzed. Nomenclatureof vortex above tip path plane, m I = intensity count K = Gladstone-Dale constant, m 3 · kg −1 M = optical magnification factor Ma = Mach number n = refractive index of air N b = number of rotor blades R = rotor radius, m T = rotor thrust, N t = time, s u, v, Δy = image displacements, m x, y, z = coordinates, m Z B= distance background -camera lens, m Z D = distance background-phase object, m Z i = distance camera lens-camera sensor, m ϵ y = deflection angle, rad ρ = density of air, kg · m −3 σ = solidity; N b · c · πR −1 Ψ = azimuth; Ωt, rad ψ v = vortex age, rad Ω = rotor rotational frequency, rad · s −1 ω z = rotation of the image displacement; ∂v∕∂x − ∂u∕∂y

free shear flows [circular jets Scarano 2011), wakes (Scarano andPoelma 2009)] and boundary layer flow (Atkinson et al. 2010). Recently a number of timeresolved tomo-PIV measurements of unsteady flows have been conducted using high speed cameras (Elsinga and Marusic 2010;Schröder et al. 2008Schröder et al. , 2011. It was shown that the obtained spatio-temporal data can be used to identify dynamic modes of the flow field (Schmid et al. 2012). The first application of tomo-PIV to internal flows in complex geometries is due to Buchmann et al. ( 2011) who studied the flow in the human carotid artery, comparing stereoscopic to tomographic PIV results under steady flow conditions. Buchmann et al. (2011) reported bias errors due to ghost particles in tomo-PIV measurements and discrepancies in the RMS error between stereo and tomo-PIV in certain regions of elevated velocity gradients of up to 10 %. Furthermore, RMS errors where found to be higher for thicker light sheets used in the tomo-PIV measurements. Overall a good agreement between the stereo PIV and the tomo-PIV results was found with RMS errors varying in the range of 0.1-0.3 pixels. A detailed presentation of tomographic PIV, its background and a wide range of applications is given in the topical review paper by Scarano (2012).This study presents the first tomo-PIV measurement of the flow past a bioprosthetic heart valve. In contrast to socalled mechanical heart valves (e.g., made of titanium and pyrolytic carbon), bioprosthetic valves are fabricated from biological tissue (e.g., bovine pericardium). Prostheses are used to replace diseased native heart valves (e.g., stenotic or insufficient valves) most often in aortic position.The design of bioprosthetic heart valves is motivated by the anatomy of native aortic heart valves with three cusps. It is believed that this biomimetic design leads to blood flow which is similar to the physiological flow

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The anomalous dispersion of an atomic line filter near a resonant transition is exploited for full-field frequency measurements. The influence of the line shape function on the dispersion in atomic vapors near resonance and the possibilities to increase sensitivity are discussed. From the model-calculated absorption of iodine vapor at frequency-doubled Nd:YAG laser wavelengths, the corresponding refractive index is obtained through the Kramers-Kronig relations. Both variables are used to assess the performance of a iodine vapor cell as a dispersive element in an interferometric setup for Doppler frequency shift detection. With good agreement, the predicted sensitivity of the setup is compared to an experimental calibration. Observed discrepancies are attributed to the assumption of a Gaussian line shape in the absorption model. The full-field Doppler frequency measurement capacity of the technique is demonstrated in a rotating disk experiment, and the measurement performance is assessed.

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