Jakob Woisetschläger

• Dr.techn. , ao.Univ.-Prof.
• Graz University of Technology

This study investigates the removal of per- and polyfluoroalkyl substances (PFAS) using a hyperbolic vortex plasma discharge under various plasma-atmospheric conditions demonstrating varied degradation times for PFAS of different chain lengths. Experiments with spiked long-chain perfluorooctane sulfonic acid in deionized (DI) water show that bipola...

This paper presents an experimental study comparing the aeration efficiencies of hyperbolic funnels and a cylindrical reactor, focusing on key parameters such as dissolved oxygen (DO) concentration, standard oxygen transfer rate (SOTR20), and standard aeration efficiency (SAE). The unique geometry of the hyperbolic funnel induces a helical water fl...

In aircraft engines, thermoacoustic oscillations in the combustion chamber contribute significantly to noise emissions, which, like all other emissions, must be drastically reduced. Thermoacoustic oscillations are not only a concern, they can also be beneficial in hydrogen combustion. This work demonstrates that thermoacoustic density oscillations...

Experimental investigations into the characterization of vortices in hyperbolic funnels have shown efficient aeration properties. Certain regimes of vortices have been observed to exhibit high gas dissolution rates. This phenomenon has prompted inquiries into the underlying physical mechanisms at both micro and macroscopic scales. The present study...

Planar velocity measurements using the particle image velocimetry technique have been performed at a repetition rate of 10 kHz in the prechamber of a large bore gas engine mounted on a rapid compression machine (RCM), to visualize the velocity fields in the non-reacting gas flow during a compression stroke. The prechamber investigated in this work...

Thermoacoustic oscillations are well known to combustion engineers. They are not only a cause of concern, but also give hope to be able to operate aircraft engines with hydrogen, due to flame stabilization and significant reduction of NOx emissions when thermoacoustically excited. The aim of this work is to investigate the potential of using a hete...

Achieving stable, low-emission combustion with green hydrogen is crucial for climate-neutral ground-based power generation in turbomachinery. Lean combustion modes with green hydrogen reduce fuel consumption but increase unsteadiness. Thus, multimodal detection techniques for parameters like density and flow velocity are essential to understand the...

The present study focuses on the characterization of a hyperbolic vortex plasma reactor through the comparison of various plasma-atmospheric regimes for the production efficiency of reactive nitrogen (RNS) and reactive oxygen (ROS) species. The research also explores effectiveness in the removal of micropollutants, including pharmaceuticals and per...

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The urgent need to reduce the emission of greenhouse gases, in combination with high fuel expenses, motivates manufacturers to design more efficient civil aircraft engines. In the case of directly driven jet engines, this is possible through the increased by-pass ratios for high propulsive efficiencies. This tendency implies a change in the operati...

Reducing greenhouse gas emissions and high fuel expenses motivates manufacturers to design more efficient aircraft engines. Efficiency can be improved for directly driven jet engines through increased by-pass ratios for high propulsive efficiencies. This measure implies a change in the operating condition of the low-pressure turbine (LPT) towards l...

Aeration is one of the most cost intensive steps in water and wastewater treatment due to the large energy requirement for the creation of large surfaces for sufficient gas exchange as well as for providing efficient liquid transport in order to exchange saturated liquid elements at the surface with unsaturated ones from the bulk. In this work we s...

Lean premixed combustion technology became state of the art in recent heavy-duty gas turbines and aeroengines. In combustion chambers operating under fuel-lean conditions, unsteady heat release can augment pressure amplitudes, resulting in component engine damages. In order to achieve deeper knowledge concerning combustion instabilities, it is nece...

A measurement technique for recording convective heat transfer coefficient and adiabatic film cooling effectiveness in demanding environments with highly curved surfaces and limited optical access, such as turbomachinery, is presented. Thermography and tailor-made flexible heating foils are used in conjunction with a novel multistep calibration and...

A horizontal electrohydrodynamic (EHD) liquid bridge (also known as a “floating water bridge”) is a phenomenon that forms when high voltage DC (kV·cm⁻¹) is applied to pure water in two separate beakers. The bridge, a free-floating connection between the beakers, acts as a cylindrical lens and refracts light. Using an interferometric set-up with a l...

Environmental protection is today’s major issue in the development of turbomachines. Especially, the reduction of pollutant and noise emission of aero engines and ground based gas turbines for power plants is a central task. Therefore, an improved understanding of the occurring complex flow phenomena in such turbomachines is necessary, which requir...

This work discusses nuclear magnetic relaxation effects in glycerol subject to a strong electric field. The methods used are 1.5 T magnetic resonance imaging (MRI), referenced by 9.4 T nuclear magnetic resonance (NMR). While MRI allows a glycerol probe to be sampled with a high voltage (HV) of 16 kV applied to the probe, NMR provides precise molecu...

The original published article contains error in equation and reference.

Modern, lean and premixed gas turbine combustion concepts for low NOx emissions are prone to combustion instabilities. In a previous work it was shown that laser interferometric vibrometry (LIV) can be used to record global as well as local heat release fluctuations in swirl-stabilized premixed methane flames quantitatively, if other effects influe...

During four solar eclipse events (two annular, one total and one partial) a correlation was observed between a change in water surface tension and the magnitude of the optical coverage. During one eclipse, evaporation experiments were carried out which showed a reduction in water evaporation at the same time as a rise in the surface tension. The ch...

In this work we expand on findings previously reported [Wexler et al., PCCP, 2016, 18, 16281] on the experimental observation of a phase transition in a hydrogen bonded liquid manifesting in long range dipole-dipole interactions. The studied system, liquid water stressed by an electric field, exhibits collective oscillations brought about through s...

In a horizontal electrohydrodynamic bridge experiment, protons are created at the anode via high-voltage electrolysis. The hydrated protons can be observed both optically using shadowgraphy and Raman spectroscopy. If the system is taken out of its electrochemical equilibrium by a sudden disruption of the bridge, excess protons remain in the anolyte...

In modern gas turbines for power generation and future aircraft engines, the necessity to reduce NOx emissions led to the implementation of a premixed combustion technology under fuel-lean conditions. In the combustion chamber of these systems, extreme pressure amplitudes can occur due to the unsteady heat release, reducing component life time or c...

Fluctuations in heat release, hot and cold spots convected by the flow and sound waves are all related to density fluctuations, a number easily detected by interferometry. Same as chemiluminescence, interferometry is a line-of-sight method and therefore needs optical access and tomographic reconstruction of density fields. In this work we discuss t...

Information about heat release can be used to discuss the flame dynamics and stability behavior of turbulent combustion systems. The most common experimental approach to determine heat release fluctuations is the recording of OH*-chemiluminescence. Since there is a strong dependence of chemiluminescence on strain rate and mixture gradients, spatial...

Flow in turbomachines is generally highly turbulent. Nonetheless, boundary layers may exhibit laminar-to-turbulent transition, and relaminarization of the turbulent flow may also occur. The state of flow of the boundary layer is important since it influences transport phenomena like skin friction and heat transfer. In this paper, relaminarization i...

Modern gas turbines rely more and more on premixed combustion systems. While they produce less emission, they are more prone to combustion instabilities. The combustion noise emitted by turbulent swirl-stabilized flames can be calculated directly if density fluctuations in the flame are known as a function of time and space. Recently it was shown t...

For turbulent swirl-stabilized flames combustion noise can be directly calculated, if density fluctuations as a function of time and space are known. It is however not easily possible to assess the density fluctuations directly. Therefore, in the past, combustion noise has been expressed as a function of chemiluminescence, an approach bringing in m...

The goal of this study was to measure the Flame Transfer Function of a perfectly and a partially premixed turbulent flame by means of Laser Interferometric Vibrometry. For the first time, this technique is used to detect integral heat release fluctuations. The results were compared to classical OH*- chemiluminescence measurements. Effects of equiva...

This 5 day-course is offered to undergraduate students at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. Goal of the course is to give students an holistic education and to train a “understanding of systems function as wholes”. Within this course students are designing an axial turbine stage from the...

For turbulent swirl-stabilized flames combustion noise can be directly calculated, if density fluctuations as a function of time and space are known. It is however not easily possible to assess the density fluctuations directly. Therefore, in the past, combustion noise has been expressed as a function of chemiluminescence, an approach bringing in m...

Flow in turbomachines is generally highly turbulent. The boundary layers, however, often exhibit laminar-to-turbulent transition. But also relaminarization of the turbulent flow may occur. The state of the boundary layer is important, since it strongly influences transport phenomena like skin friction and heat transfer. It is therefore vitally impo...

Flow in turbomachines is generally highly turbulent. The boundary layers, however, often exhibit laminar-to-turbulent transition. Relaminarization from turbulent to laminar flow may also occur. The state of the boundary layer is important since it strongly influences transport processes like skin friction and heat transfer. It is therefore vitally...

In this experiment liquid water is subject to an inhomogeneous electric field (${\nabla}^2 E_a {\approx} 10^{10} \frac{V}{m^2}$ ) using a high voltage (20 kV) point-plane electrode system. With interferometry it was found that the application of a strong electric field gradient to water generates local changes in the refractive index of the liquid,...

Here we report on the feasibility and use of magnetic resonance imaging based methods to the study of electrohydrodynamic (EHD) liquid bridges. High speed tomographic recordings through the longitudinal axis of water bridges were used to characterize the mass transfer dynamics, mixing, and flow structure. By filling one beaker with heavy water and...

Here we report on the feasibility and use of magnetic resonance imaging based methods to the study of electrohydrodynamic (EHD) liquid bridges. High speed tomographic recordings through the longitudinal axis of water bridges were used to characterize the mass transfer dynamics, mixing, and flow structure. By filling one beaker with heavy water and...

In this experiment liquid water is subject to an inhomogeneous electric field (${\nabla}^2 E_a {\approx} 10^{10} \frac{V}{m^2}$ ) using a high voltage (20 kV) point-plane electrode system. With interferometry it was found that the application of a strong electric field gradient to water generates local changes in the refractive index of the liquid,...

In a floating water bridge the total radiation scattering of water stressed by a moderately strong electric field (1mV/nm) was compared to water without an applied electric field using X-ray and small angle neutron scattering. Structure refinement was carried out using the EPSR method and the TIP4P/2005 water model. These results did not reveal a s...

Excess positive and negative Bjerrum-defect like charge (protonic and 'aterprotonic', from ancient Greek ατερ, 'without') in anolyte and catholyte of high voltage electrolysis of highly pure water was found during the so-called 'floating water bridge' experiment. The floating water bridge is a special case of an electrohydrodynamic liquid bridge an...

We have measured the quasi-elastic neutron scattering (QENS) of an electrohydrodynamic liquid bridge formed between two beakers of pure water when a high voltage is applied, a set-up allowing to investigate water under high-voltage without high currents. From this experiment two proton populations were distinguished: one consisting of protons stron...

This work reports on proton production, transport, reduction and neutralization in floating aqueous bridges under the application of a high dc voltage (‘floating water bridge’). Recently possible mechanisms for proton transfer through the bridge were suggested. In this work we visualize and describe the production of protons in the anolyte and thei...

The goal of the study presented in this paper is to analyze flame transfer functions with a new approach based on the combination of-line-of sight OH*-chemiluminescence and density fluctuation data. The OH*-chemiluminescence is acquired with a photomultiplier and an intensified camera, the density fluctuations are measured with a Laser vibrometer o...

In this work, an atmospheric model combustion chamber was characterized employing Laser Vibrometry, chemiluminescence and Particle Image Velocimetry. The test object was a variable geometry burner enclosed with a liner, with the flame optically accessible through four fused silica windows. In this burner with adjustable flame conditions the cavity...

A novel technique for time- and space-resolved measurement of density fluctuation is presented. It is nonintrusive and based on laser Doppler vibrometry. The density fluctuations reveal information on dynamic heat release and fluid velocity. The significance of this technique is proven by recording thermo-acoustic oscillations in a model combustor.

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and polar dielectric liquids. These bridges are unique from capillary bridges in that they exhibit extensibility beyond a few millimeters, have complex bi-directional mass transfer patterns, and emit non-...

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 pe...

Modern aircraft engines operate with a reduced core air mass flow, which is challenging regarding an efficient and most of all stable combustion of fuel. A variable geometry burner investigated here allows a stable lean combustion with lower air mass flow rate than with a fixed geometry. In order to optimize such burners further, the occurring flam...

In this work, investigations of thermo-acoustic oscillations by means of density fluctuation measurements, are presented. For this, laser-vibrometers were used. Although these systems were initially developed for highly accurate detection of surface vibration, they are also capable of measuring the integral gas density fluctuation along the line of...

When a high-voltage direct-current is applied to two beakers filled with water or polar liquid dielectrica, a horizontal bridge forms between the two beakers. This experiment was first carried out by Lord Armstrong in 1893 and then forgotten until recently. Such bridges are stable by the action of electrohydrodynamic (EHD) forces caused by electric...

Introducing a new measurand, namely the rate of change of density in line-of-sight, can be of great interest for people working on thermoacoustics and combustion noise. In this work the relationship between the radiated acoustic pressure, the time rate of change of unsteady heat release and of density fluctuations in a laminar pulsated premixed fla...

We report on the infrared emission of aqueous bridges under the application of high dc voltage ('floating water bridge') over the range between 400 and 2500 cm −1 (4.0–10.3 µm). Comparison with bulk water of the same temperature reveals an additional broad peak at ∼2200 cm −1 as well as water vapour emission lines. Two complementary explanations ar...

A study on innovative gas turbine core concepts supported by the NEWAC project (NEW Aero-engine Core concepts, Integrated Project co-funded by the European Commission within the Sixth Framework Programme under contract No. AIP5-CT-2006-030876) focused on the ability of the combustor to maintain combustion during a drastic reduction of the main air,...

When a high-voltage direct-current is applied to two beakers filled with polar liquid dielectrica like water or methanol, a horizontal bridge forms between the two beakers. By repeating a version of Pellat’s experiment, it is shown that a horizontal bridge is stable by the action of electrohydrodynamic pressure. Thus, the static and dynamic propert...

When a high-voltage direct-current is applied to two beakers filled with water or polar liquid dielectrica, a horizontal bridge forms between the two beakers. In this work such bridges made of methanol, ethanol, 1-propanol and 2-propanol are investigated with polarimetry and thermography. Whereas methanol, ethanol and 1-propanol bridges become warm...

Abatract—A novel device called the Bioscope System is investigated for feasibility as sensor for chemicals in aqueous solutions. Thereby a sample is examined by a pulsed voltage and electrical properties of that sample are measured. These electrical properties can be considered as a sum parameter of the sample in terms of conductivity and permittiv...

When high voltage is applied to distilled water filled into two beakers close to each other, a watery connection forms spontaneously, giving the impression of a floating water bridge [1-8]. In this work we present the first inelastic ultraviolet scattering data of such an electrohydrodynamic bridge revealing radial gradients of Stokes-and Anti-Stok...

When high voltage is applied to pure water filled into two beakers close to each other, a connection forms spontaneously, giving the impression of a floating water bridge (Armstrong 1893 The Electrical Engineer pp 154–45, Uhlig W 2005 personal communication, Fuchs et al 2007 J. Phys. D: Appl. Phys. 40 6112–4, Fuchs et al 2008 J. Phys. D: Appl. Phys...

Experimental measurements of spatially- and frequency-resolved density fluctuations in two different types of flames, a non-premixed methane-jet flame and a premixed swirlstabilized methane-air flame were performed in this work. A novel interferometric measurement technique was applied for this purpose. Two laser vibrometers together with a signal...

When high voltage is applied to pure water filled into two beakers close to each other, a connection forms spontaneously, giving the impression of a floating water bridge 1-8 . This phenomenon is of special interest, since it comprises a number of phenomena currently tackled in modern water science. In this work, the charge and mass transfer throug...

A validation of a novel interferometric measurement technique for the frequency-resolved detection of local density fluctuation in turbulent combustion analysis was performed in this work. Two laser vibrometer systems together with a signal analyser were used to obtain frequency spectra of density fluctuations across a methane-jet flame. Since lase...

This paper presents an experimental investigation of the flow field in a high-pressure transonic turbine with a downstream vane row (1.5 stage machine) concerning the airfoil indexing. The objective is a detailed analysis of the three-dimensional aerodynamics of the second vane for different clocking positions. To give an overview of the time-avera...

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., ASME Turbo-Expo 2006, GT 2006-90413). This paper reports on the mapping of density fluctuations measured with...

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 phe...

The current paper presents the final results of an extensive experimental and numerical clocking investigation performed in a high-pressure transonic turbine with a downstream vane row (1.5 stage machine). A transient 3D-Navier Stokes calculation was performed for two clocking positions and the three dimensional results are compared with Laser-Dopp...

In a high-voltage direct-current experiment, a watery connection formed between two beakers filled with deionized water, giving the impression of a ‘floating water bridge’. Having a few millimeters diameter and up to 2.5cm length, this watery connection reveals a number of interesting phenomena currently discussed in water science. Focusing on opti...

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...

The current paper presents the results of numerical and experimental clocking investigations performed in a high-pressure transonic turbine with a downstream vane row. The objective was a detailed analysis of shock and wake interactions in such a 1.5-stage machine while clocking the vanes. Therefore, a transient 3D Navier-Stokes calculation was don...

The paper presents an experimental investigation of the flow field in a high-pressure transonic turbine with a downstream vane row (1.5 stage machine) concerning the airfoil indexing. The objective is a detailed analysis of the three dimensional flow field downstream of the high pressure turbine for different vane clocking positions. To give an ove...

The unsteady and fully three-dimensional aerodynamics of HP turbines represent a relevant research branch for future aero-engine design. When stator-rotor interaction mechanisms and clocking effects are of concern, advanced measurement techniques as well as unsteady CFD codes are required. An extensive study on this topic was carried out in a one a...

This paper focuses on the visualization of both experimental and numerical results and presents research in a highly-loaded cold-flow transonic turbine under continuous and engine-representative conditions. Special focus was placed on blade row interaction at app. 10600 rpm. While the first step was the investigation of a single stage machine (stat...

During the past decade particle image velocimetry(PIV) has become a versatile tool in the investigation of flow fields in turbomachinery. In this overview a short summary on recent applications ofPIV in these machines is given, with a focus on rotating turbine and compressor test rigs and the developments within the PivNet network funded by the Eur...

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.

A one and a half stage transonic turbine was tested using a two component laser–doppler–velocimetry system. The measurements were carried out in order to record rotor phase resolved velocity, flow angle and turbulence distributions upstream and downstream of the second stator row at several different angular stator–stator positions (“clocking” posi...

The current paper presents the results of numerical clocking investigations performed in a high-pressure transonic turbine with a downstream vane row (1.5 stage machine). A transient 3D-Navier Stokes calculation was done for four clocking positions and the three dimensional results are compared with Laser-Doppler-Velocimetry measurements at midspan...

The current paper presents experimental clocking investigations of the flow field in midspan in a high-pressure transonic turbine with a downstream vane row (1.5 stage machine). Laser-Doppler-Velocimetry measurements were carried out in order to record rotor phase resolved velocity, flow angle and turbulence distributions upstream and downstream of...

The current paper presents steady and unsteady flow data of a transonic test turbine stage operating under flow conditions similar to modern highly loaded gas turbines. Measurements were performed between stator and rotor as well as downstream of the rotor in planes perpendicular to the rotor axis. Time-resolved axial and tangential velocities were...

Laser vibrometry (LV) is originally a laser-based measurement technique dedicated to the analysis of surface vibrations. This technique was adapted at TU Graz as a line-of-sight measurement technique for the observation of coherent vortices in a turbulent flow, and then lately as a technique for monitoring the stability of an air-methane flame usin...

The objective of this work was the application of interferometry as a tool for non-intrusive measurement of frequency spectra in turbulent flows. Two laser vibrometer systems together with a signal analyser were used to obtain the frequency spectra of density fluctuations across a fully developed turbulent free jet. Since laser vibrometry is based...

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 v...

Laser-based diagnostics for combustion monitoring are promising sensing techniques for the upcoming generation of build-in gas turbines measurement and control devices. Their principles are usually based on direct measurement of line-of-sight transmission, absorption, scattering or re-emission of laser light through the flame. We discuss here how a...