The transition of the cylinder wake is investigated experimentally in a water channel and is computed numerically using a finite-difference scheme. Four physically different instabilities are observed: a local "vortex-adhesion mode," and three near-wake instabilities, which are associated with three different spanwise wavelengths of approximately 1, 2, and 4 diam. All four instability processes can originate in a narrow Reynolds-number interval between 160 and 230, and may give rise to different transition scenarios. Thus, Williamson's [Phys. Fluids 31, 3165 (1988)] experimental observation of a hard transition is for the first time numerically reproduced, and is found to be induced by the vortex-adhesion mode. Without vortex-adhesion, a soft onset of three-dimensionality is numerically and experimentally obtained. A control-wire technique is proposed, which suppresses transition up to a Reynolds number of 230.

A coupled Landau model describing the Strouhal-Reynolds number profile of a three-dimensional circular cylinder wake Phys. Fluids 15, L68 (2003);

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The identification of laminar-turbulent boundary layer transition on wind tunnel models provides essential data for modem wing design. However, simulating true flight Reynolds numbers with scaled models requires the use of cryogenic wind tunnels. Transition detection in 'war" wind tunnels can be realized using commercially available IR cameras. In parallel, the temperature sensitive paint (TSP) technique is well established as an additional tool. In cryogenic testing IR i m g n g becomes more difficult because of the reduction in radiated energy and the shift to longer wavelengths. Therefore, the TSP technique has become a promising alternative here. However, applying temperature sensitive paint in a large-scale cryogenic wind tunnel like the EuropeanTransonic Wind tunnel (ETW) needs specific modification of existing TSP formulations. Cooperative tests in the ETW therefore were performed by DLR and NAL (Japan). In these measurements, NAL's paint and DLR's mobile PSP/TSP system for data acquisition and evaluati~n'.~.' were used. Some efforts were m d e to adapt the system to specific conditions given at the ETW wind tunnel. So for the first time it was successfully realized to perform a TSP luminescent paint test at cryogenic temperatures in a commercial wind tunnel. Nomenclature Re =Reynolds number Ma =Machnumber p,, T AT 6T a =angle ofattack CL =lift coefficient x*,y*,z* =wing coordinates S = half wing span of model rl =normalized spanwise coordinate (y*/s) x/c =normalized chordwise coordinate = stagnationpressure/temperature in tunnel =total a m u n t of temperature change = temperature difference on wing THE CRYOGENIC WIND TUNNELThe European Transonic Wind tunnel (ETW) sited in Cologne, Germny, i s an industrial cryogenic pressurized facility. It provides the capability for achieving full scale flight Reynolds numbers of transport aircrafi by testing at pressures between 125 and 450 !@a and at temperatures between 110 and 310 K, using nitrogen as the test gas. The tunnel started operation in 1994, and, after a phase of commissioning and evaluation, it is available for productive testing since 19964. Aerodvnarrdc CircuitThe ETW has a closed aerodynamic circuit contained inside an intemally insulated pressure shell. The two stage, fixed blade compressor are driven by a 50 MW synchronous motor. To achieve the desired low tem perahues of the test gas, liquid nitrogen is injected continuously into the tunnel upstream of the compressor. The corresponding gaseous nitrogen exhaust upstream of the stilling chamber is contmlled by valves for the accurate maintenance of tunnel pressure. From the settling chamber equipped with a honeycomb and anti-turbulence screens, the flow enters the test section via a flexible nozzle of contraction ratio 1 : 12 (&I). Figure 1: Aerodynamic circuit of the ETW wind tunnel. LN2: liquid nitrogen, GN2: gaseous nitrogen. 0-7803-8 149-1/03/$17.0002003 IEEE 77The test section has slots in the top and bottom wall for full span model tests and slotted side walls for half model tests. Mach number...