Jakob Woisetschläger

The floating water bridge

When high voltage is applied to distilled water filled in two glass beakers which are in contact, a stable water connection forms spontaneously, giving the impression of a floating water bridge. A detailed experimental analysis reveals static and dynamic structures as well as heat and mass transfer through this bridge.

Dynamics of the floating water bridge

When high voltage is applied to distilled water filled into two beakers close to each other, a water connection forms spontaneously, giving the impression of a floating water bridge (Fuchs et al 2007 J. Phys. D: Appl. Phys. 40 6112–4). This phenomenon is of special interest, since it comprises a number of phenomena currently tackled in modern water science. The build-up mechanism, the chemical properties and the dynamics of this bridge as well as related additional phenomena are presented and discussed.

Neutron scattering of a floating heavy water bridge

When high voltage is applied to distilled water filled into two beakers close to each other, a water connection forms spontaneously, giving the impression of a floating water bridge (Fuchs et al 2007 J. Phys. D: Appl. Phys. 40 6112–4, 2008 J. Phys. D: Appl. Phys. 41 185502). This phenomenon is of special interest, since it comprises a number of phenomena currently tackled in modern water science. In this work, the first data on neutron scattering of a floating heavy water bridge are presented and possible interpretations are discussed. D2O was measured instead of H2O because of the very strong incoherent scattering of H. The obtained data support the ‘bubble hypothesis’ suggested earlier (Fuchs et al 2008).

Comparison of Different Methods of Abel Inversion Using Computer Simulated and Experimental Side-On Data

Abstract A recently devised new method for numerical Abel inversion is compared with four other commonly used methods. One of them, the convolution method, is employed in computer tomography for reconstructing asymmetrical objects. It is investigated whether this method can be adapted for the case of radial symmetry. As a first approach the comparison is performed by computer simulation. Special attention is given to the propagation of errors according to their origin. The result is a recipe for minimizing errors and for choosing the optimal method for reconstruction. The second step is a comparison of experimentally obtained radial profiles with functions resulting from Abel inversion of measured side-on data. Thus it is shown that the concept developed by computer simulation can be applied in practice

Investigation of Vortex Shedding and Wake-Wake Interaction in a Transonic Turbine Stage Using Laser-Doppler-Velocimetry and Particle-Image-Velocimetry

The current paper presents a time-resolved experimental flow investigation in a highly loaded transonic gas turbine stage operating continuously under engine representative conditions. The measurement was performed with a two-component laser-doppler-velocimeter (LDV) and a three-component stereoscopic particle-image-velocimeter (3C-PIV). Unsteady velocity data were obtained in axis perpendicular planes (LDV) and tangential planes (3C-PIV) between stator and rotor as well as downstream of the rotor. The results of the time-resolved investigation at several radii show the vortex shedding process from the trailing edges of nozzle guide vanes and rotor blades. This vortex shedding was found to be phase locked to higher harmonics of the blade passing frequency. Pressure waves evoked by reflection of the trailing edge shocks of the vanes on the passing rotor blades interact with the boundary layers on the rear suction side of the vanes and on the rotor blade surfaces while running upstream and downstream the flow. They are responsible for this phase-locking phenomenon of the shedding vortices. At midspan, the vortices shedding from stator and rotor blades were also observed by PIV. The in-plane vorticity distribution was used to discuss the wake-wake interaction indicating that wake segments from the nozzle guide vanes were chopped by the rotor blades. These chopped segments are still visible in the distributions as a pair of counter rotating vortices. The nozzle wake segments are transported through the rotor passages by the flow, influencing the vortex street of the rotor blades as they pass by with the higher velocity of the main flow. A comparison with a numerical simulation is also given.

Optical tomography of phase objects by holographic interferometry

Abstract Computer-aided optical tomography by laser probing performed on the basis of holographic interferometry is a powerful tool for the experimental determination of the spatially resolved distribution of the refractive index for distinct cross-sections through a phase object. In comparison with X-ray computer tomography there exist some complications in the optical domain, such as saturation effects in the case of resonance interferometry and the danger of ray bending because of refractive index gradients inside the object zone. Besides the discussion of the optical arrangements, of the evaluation of the interferograms by Fourier analysis and of the tomographic reconstruction algorithms used, the priority of this paper is set on a discussion of some experimental checks for the degree of possible falsifications of the reconstruction caused by ray bending.

Transition Modeling Using Two Different Intermittency Transport Equations

The accurate numerical simulation of the flow through turbomachinerydepends on the correct prediction of boundary-layer transitionphenomena. Especially heat transfer and skin friction investigationsdemand a reliable simulation of the transition process.Therefore, in this work two different one-equation transport modelsfor a transitional weighting factor are selected and modified for theimplementation into a Reynolds-averaged Navier–Stokes solver. Thisfactor is used to modify the eddy viscosity obtained from a turbulencemodel to simulate the transition process. The first model was originallydeveloped by Steelant and Dick [1] to simulate by-passtransition for high free-stream turbulence. The second model wasproposed by Huang and Suzen [2] as a blending of two modelsfor near-wall intermittency and cross-stream variation of intermittency.In contrast to one-dimensional transition models, the new approachesmodel the transition process not only in flow direction but also acrossthe boundary-layer and thus provide a more realistic prediction of thetransition process. Whereas the Steelant and Dick model (SD) allowsturbulent quantities in the free-stream prior and after transition, thesecond model by Huang and Suzen (HS) sets the free-stream turbulence tozero in the whole flowfield.The models are validated on transitional skin friction experimentson a flat plate (T3 test cases of ERCOFTAC SIG 10), on heat transfermeasurements in a linear turbine cascade done at the VKI and on laservibrometer measurements of a linear turbine cascade. Both models showgood agreement with the skin friction data, but the heat transfer canonly be predicted correctly by the Steelant and Dick model due to itsability to consider the free-stream turbulence.

Tomographic reconstruction of the temperature distribution in a convective heat flow using multidirectional holographic interferometry.

Multidirectional interferometric data of an inhomogeneous phase object are obtained by double exposure reflection type holography. The evaluation of the interferograms for a computerized tomographic reconstruction of the local index of refraction by the convolution method is performed with subfringe resolution. For testing purposes the phase object is made by careful modeling of a convective heat flow in air. The reconstructed refractive index field is converted into a temperature distribution and is compared with independently measured temperature values, thus providing a strict examination of the quality of the tomograms.

Mapping the Density Fluctuations in a Pulsed Air-Methane Flame Using Laser-Vibrometry

Laser vibrometry (LV) is originally a laser-based, line-of-sight measurement technique dedicated to the analysis of surface vibrations. It was lately adapted at TU Graz for monitoring the stability of an air-methane flame (Giuliani, et al., 2006, ASME Turbo Expo, ASME Paper No. GT2006-90413). This paper reports on the mapping of density fluctuations measured with LV in a premixed air-methane flame (free jet; swirl stabilized) with a forced flow modulation (quarter-wave resonator; amplification with a siren). In order to correlate the density fluctuations with the jet aerodynamics and turbulent flame shape, stereoscopic particle image velocimetry and high-speed schlieren visualizations were used. This paper addresses issues regarding the estimate of density fluctuations, the transform from line-of-sight to local measurement with tomographic methods, and the potential of the method for detailed description of thermoacoustic couplings. One emphasized application of LV is its ability to perform precise and low-cost benchmark stability tests on a combustor during the design phase (time-resolved measurement, high frequency and phase resolution on the 5 Hz―20 kHz range with the present equipment and settings, near-constant spectral sensitivity over a large bandwidth, and no seeding required ; measurement possible over the whole combustion volume).

Phase-shifting holographic interferometry for breast cancer detection

Using a mild pressure stressing device and a pulsed ruby-laser system, we apply phase-shifted holographic interferometry to the detection of breast cancer. We compare a four-step algorithm and a Carré algorithm for their ability to evaluate the interferograms. The results show the feasibility of holographic interferometry in the detection of anomalies in the human female breast.