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Abstract 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 data reduction method. This method compensates for sensor drift, angle dependence of surface emissivity and window transmissivity, heat flux inhomogeneity, and conductive losses. The 2D infrared images are mapped onto the 3D curved surfaces and overlapped, creating surface maps of heat transfer coefficient and film cooling effectiveness covering areas significantly larger than the window size. The measurement technique’s capability is demonstrated in a sector-cascade test rig of a turbine center frame (TCF), an inherent component of modern two-spool turbofan engines. The horseshoe vortices were found to play a major role for the thermal integrity of turbine center frames, as they lead to a local increase in heat transfer, and at the same instance, to a reduction of film cooling effectiveness. It was also found that the horseshoe vortices lift off from the curved surface at 50% hub length, resulting in a pair of counter-rotating vortices. The measurement technique was validated by comparing the data against flat plate correlations and also by the linear relation between temperature difference and heat flux. This study is complemented with an extensive error and uncertainty analysis. Article highlights This paper presents an accurate measurement technique for heat transfer and film cooling on 3D curved surfaces with limited optical access using flexible tailor-made heating foils, infrared thermography and a high-fidelity multistep calibration process. Graphical abstract

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 molecular data from the sample, but the sample cannot be tested under HV. Using MRI, the recording of magnetic relaxation times was possible while HV was applied to the glycerol. NMR spectroscopy was used to confirm that MRI provides a reasonably accurate estimation of temperature. The applied HV was observed to have a negligible effect on the spin–lattice relaxation time T1, which represents the energy release to the thermal bath or system enthalpy. In contrast to that, the spin–spin relaxation time T2, which does represent the local entropy of the system, shows a lower response to temperature while the liquid is electrically stressed. These observations point toward a proton population in electrically stressed glycerol that is more mobile than that found in the bulk, an observation that is in agreement with previously published results for water.

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 show that geometrically constrained vortices in a hyperbolic funnel are a promising aeration technique as they meet these criteria and allow oxygen transfer coefficients up to 50 h−1, a number significantly higher than that of comparable methods like air jets or impellers (−1).

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 changes did not occur on a day without a solar eclipse and are not correlated to changes in temperature, pressure, humidity of the environment. The effects are delayed by 20, 85, 30 and 37 min, respectively, compared to the maximum eclipse. Possible mechanisms responsible for this effect are presented, the most likely hypothesis being reduced water/muon interaction due to solar wind and cosmic radiation blocking during an eclipse. As an alternative hypotheses, we propose a novel neutrino/water interaction and overview of other, less likely mechanisms.

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 the use of Laser Interferometric Vibrometry (LIV) as an alternative or extension to chemiluminescence when detecting heat release fluctuations in the flame, convection of hot and cold spots in the non-reacting flow field and sound waves emitted from a 3.4 kW turbulent, unconfined swirl-stabilized methane/air flame under perfectly premixed conditions. For this discussion local temperatures, local ratios of heat release and local Gladstone-Dale constants are determined and their influence on the result discussed. Global and local fluctuations in heat release rate recorded by LIV and chemiluminescence are compared, resulting in the same global values if local temperature fields and local equivalence ratios are used for LIV data evaluation. In contrast, local fluctuations in OH* chemiluminescence emission are influenced by turbulence and strain in this type of flame.

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 line pattern placed in the background of the bridge, the light passing through is split into a horizontally and a vertically polarized component which are both projected into the image space in front of the bridge with a small vertical offset (shear). Apart from a 100 Hz waviness due to a resonance effect between the power supply and vortical structures at the onset of the bridge, spikes with an increased refractive index moving through the bridge were observed. These spikes can be explained by an electrically induced liquid–liquid phase transition in which the vibrational modes of the water molecules couple coherently.

The original published article contains error in equation and reference.

Abstract 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 influencing density are small. In this work a newly developed camera-based full-field LIV system (CLIV) was applied to a lean, confined, premixed and swirl-stabilized methane flame under atmospheric conditions. Instead of time-consuming pointwise scanning of the flame, CLIV records full-field line-of-sight density fluctuations with high spatio-temporal resolution. With a recording rate of 200 kHz, CLIV enables the visualization of highly unsteady processes in fluid dynamics and combustion research. As an example for an unsteady process, the propagation of the flame front through a lean, premixed gas volume is visualized during an ignition process. A discussion of algorithms and assumptions necessary to calculate heat release oscillations from density oscillations is presented and applied to phase-averaged data recorded with CLIV for this type of flame. As reference, OH* chemiluminescence data were recorded simultaneously. While density gradients travelling with the flow are recorded by LIV and CLIV, chemiluminescence imaging will show nothing in the absence of chemical reaction. Graphic abstract a Time-averaged density gradient within the combustor in lateral direction. b Density fluctuations along line-of-sight 7 ms after ignition. c Phase-averaged and local heat release fluctuations at 225 Hz perturbation frequency

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 requires the investigation of influence and interaction of several process and flow quantities. A simultaneous detection of these quantities is needed in order to analyze the interaction by means of correlation. We present a new approach for simultaneous measurement of density fluctuations and advection velocity inside a turbulent flow without any invasive treatment of the process. Our approach is based on recent developments in the fields of high-speed camera technique and digital processing power, enabling pixel-wise detection of line-of-sight density oscillations and digital signal correlation with a high spatio-temporal resolution of 140 μ m 2 using 79000 pixel at a frame rate of 120 kHz , where the velocity measurement is performed by correlation of density vortex movement. A comparison with particle-based velocity detection is made in order to achieve new insights towards the still complicated interpretation of density-based velocity estimation.

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 information must be judged with care. As already shown in previous work, Laser Interferometric Vibrometry (LIV) directly detects the line-of-sight values of density fluctuations along the laser beam axis. Neglecting friction, losses of thermal radiation and conduction and assuming only small fluctuations of pressure in the reaction zone, heat release fluctuations can be calculated directly from density fluctuations. With available LIV techniques only pointwise scanning was feasible, resulting in time-consuming traversing of the flame to cover the whole flame field. A new camera-based full-field-LIV-system, developed at Technische Universität Dresden, is capable to simultaneously determine spatial information of heat release within the whole field with only one measurement, lasting a few minutes. This leads to a dramatical reduction of measurement time and furthermore reduces experimental efforts. Since the system is able to measure the complete flame at once, it is also possible to get information about the transient behavior of the combustion process. In this work the full-field-LIV system was applied for the first time on a swirl stabilized, lean and premixed methane flame. The results of this newly developed technique were checked against those of a commercially available single-beam LIV-system. Finally, the flame transfer function (FTF) was recorded with full-field-LIV and OH*-chemiluminescence and compared against each other.

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 setup allowing to investigate water under high-voltage without high currents. From this experiment two proton populations were distinguished: one consisting of protons strongly bound to oxygen atoms (immobile population, elastic component) and a second one of quasi-free protons (mobile population, inelastic component) both detected by QENS. The diffusion coefficient of the quasi-free protons was found to be D = (26 ± 10) × 10(-5) cm(2) s(-1) with a jump length lav ∼ 3 Å and an average residence time of τ0 = 0.55 ± 0.08 ps. The associated proton mobility in the proton channel of the bridge is ∼9.34 × 10(-7) m(2) V(-1) s(-1), twice as fast as diffusion-based proton mobility in bulk water. It also matches the so-called electrohydrodynamic or "apparent" charge mobility, an experimental quantity which so far has lacked molecular interpretation. These results further corroborate the proton channel model for liquid water under high voltage and give new insights into the molecular mechanisms behind electrohydrodynamic charge transport phenomena and delocalization of protons in liquid water.

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.

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 that laser interferometry records density fluctuations in the flame quantitatively. In this work a swirl-stabilized, rotationally-symmetric unconfined methane flame at lean operation conditions and low air mass flow rate was scanned by laser interferometric vibrometry (LIV) in order to calculate the overall sound power emitted by the flame. To validate the outcome calculated from the LIV data, sound power was also measured in a half-hemisphere by microphones, using pressure-pressure-probes. These probes record the total sound power of the combustion noise emitted by the flame. To improve signal to noise ratio for this measurement, a siren was used to generate a reproducible excitation of the flame at 212Hz. Both measurement methods were in good agreement. With the LIV data detailed information about the local density fluctuations in the flame causing the sound emission was obtained. Also a preferred acoustic propagation direction between 40° and 80° to the burner axis in downstream direction was observed. This deviation from a uniform distribution is likely to be caused by temperature gradients in the flame. A discussion of systematic errors inherent to the LIV technique and data reduction concludes this publication.

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 field gradients counteracting gravity. Due to these gradients a permanent pumping of liquid from one beaker into the other is observed. At macroscopic scale several of the properties of a horizontal water bridge can be explained by modern electrohydrodynamics, analyzing the motion of fluids in electric fields. Whereas on the molecular scale water can be described by quantum mechanics, there is a conceptual gap at mesoscopic scale which is bridged by a number of theories including quantum mechanical entanglement and coherent structures in water – theories that we discuss here. Much of the phenomenon is already understood, but even more can still be learned from it, since such “floating” liquid bridges resemble a small high voltage laboratory of their own: The physics of liquids in electric fields of some kV/cm can be studied, even long time experiments like neutron or light scattering are feasible since the bridge is in a steady-state equilibrium and can be kept stable for hours. It is also an electro-chemical reactor where compounds are transported through by the EHD flow, enabling the study of electrochemical reactions under potentials which are otherwise not easily accessible. Last but not least the bridge provides the experimental biologist with the opportunity to expose living organisms such as bacteria to electric fields without killing them, but with a significant influence on their behavior, and possibly, even on their genome.

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 flame is presented. The burner produced a ‘M’-shaped flame which is excited by harmonic modulations of the flow at two forcing frequencies f = 51 and 101 Hz. Measurements were performed by a microphone to record the sound pressure radiated by the flame in the far field, a photomultiplier to collect the light emission from which the heat release rate was estimated, and a laser vibrometer to detect the rate of change of density fluctuations within the reaction region. As the latter technique is a novel approach in combustion analysis a detailed description of the fundamentals of laser interferometric vibrometry is presented. Laser vibrometry offers the advantage to be low-demanding in terms of instrumentation and settings and to be relatively straightforward to process for a broad frequency range. The different signals recorded are correlated. An interpretation of the measurement data is given and the potential of laser vibrometry to obtain time resolved data on density and heat release rate fluctuations in the flame region is demonstrated.

The characterization of modern jet engines or stationary gas turbines running with lean combustion by means of swirl-stabilized flames necessitates seedingless optical field measurements of the flame transfer function, i.e. the ratio of the fluctuating heat release rate inside the flame volume, the instationary flow velocity at the combustor outlet and the time average of both quantities. For this reason, a high-speed camera-based laser interferometric vibrometer is proposed for spatio-temporally resolved measurements of the flame transfer function inside a swirl-stabilized technically premixed flame. Each pixel provides line-of-sight measurements of the heat release rate due to the linear coupling to fluctuations of the refractive index along the laser beam, which are based on density fluctuations inside the flame volume. Additionally, field measurements of the instationary flow velocity are possible due to correlation of simultaneously measured pixel signals and the known distance between the measurement positions. Thus, the new system enables the spatially resolved detection of the flame transfer function and instationary flow behavior with a single measurement for the first time. The presented setup offers single pixel resolution with measurement rates up to 40 kHz at an maximum image resolution of 256 px x 128 px. Based on a comparison with reference measurements using a standard pointwise laser interferometric vibrometer, the new system is validated and a discussion of the measurement uncertainty is presented. Finally, the measurement of refractive index fluctuations inside a flame volume is demonstrated.

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 very beginning and apply all the theory learned in separate courses before. At first the students design the annulus and the blades. They determine the inlet and outlet velocity triangles for several channel heights and define the camber line of the profile before a thickness distribution is superimposed. Secondly, a 3d CAD model including a disk design is created to get a realistic blade root. Then the students perform a finite element analysis (FEA) of the rotor blade and evaluate mechanical stresses in distinct sections of the blade. Also, natural frequencies are determined and a Campbell diagram is calculated. If the students have proven that there design is free from mechanical problems a steady state simulation of the flow through one passage is performed. Due to the fact that there is one numerical simulation platform for FEA as well as for CFD, a coupling of the fluid structure interaction (FSI) can be realised as final step. In a 1 way FSI analysis the students evaluate basic aeroelastic characteristics. After finishing that theoretical part an experimental part follows in which the students measure the static wall pressure distribution on the suction and pressure surface of that particular mid span profile in a subsonic wind tunnel. Natural frequencies are also experimentally determined using laser vibrometers. At the end of the course students will “produce” their own rotor blade with a 3d-printer. The blade can be kept as a souvenir. This paper describes the content of the course in detail and presents some results of last year’s class and reports the feedback of the students.

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 important for the designer to understand the process of boundary layer transition and to determine the position of transition onset and the length of the transitional region. In order to get into the details of transition and relaminarization it is helpful to study simplified test cases first. Therefore, in this paper a relaminarization test case for a simple geometry is investigated: The boundary layer flow along a flat plate is exposed to acceleration with three different acceleration parameters, which is known as a crucial parameter for relaminarization. Measurements were performed for the inlet free-stream velocities of 5 m/s and 9 m/s. Several experimental techniques for detecting transition were tested at the institute before their application. In this work, Laser-Doppler anemometry (LDA) measurements were performed, since this optical technique is non-intrusive and does not disturb the flow. Therefore it can also be used in narrow flow passages where probe blockage can be crucial. As an outcome of this study, an insight into the process of relaminarization is presented. Although the key onset values for relaminarization stated in literature are fulfilled with the test setup, full relaminarization over the whole boundary layer has not been achieved. It seems, that using only the skin friction as indicator for relaminarization is not sufficient.

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 more assumptions. Now, by using interferometry, density fluctuations in the flame can be measured quantitatively. The advantage of this technique is that it measures the time derivative of density fluctuations directly. In this work laser interferometric vibrometry (LIV) was used to scan a two dimensional field in the flame in order to calculate the sound power emitted by the flame. Sound intensity was measured in a half-hemisphere by pressure-pressure-probes in order to record the total sound power of the direct combustion noise emitted by the unconfined flame. The goal of this study was to compare the measured sound power exhibited by the flame with the sound power predicted due to fluctuations of density within the flame. By using a siren to generate linear excitation, it was possible to qualitatively predict combustion noise with good agreement in trend. A quantitative comparison between both measurement techniques showed a deviation of a factor of six.

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 equivalence ratio waves and vortex rollup were found within those flames and were then investigated by means of time resolved planar CH*/OH*-chemiluminescence and Frequency modulated Doppler global velocimetry. This work is motivated by the difficulties chemiluminescence encounters when faced with partially premixed flames including equivalence ratio waves and flame stretching. LIV, recording the time derivative of the density fluctuations as line-of-sight data, is not affected by these flame properties.

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 important for the designer to understand the process of laminar-to-turbulent transition and to determine the position of transition onset and the length of the transitional region. In order to better understand transition and relaminarization it is helpful to study simplified test cases first. Therefore, in this paper the flow along a flat plate is experimentally studied to investigate laminar-to-turbulent transition. Measurements were performed for the different free-stream velocities of 5 m/s and 10 m/s. Several measurement techniques were used in order to reliably detect the transitional zone: the Preston tube, hot wire anemometry, thermography and Laser Interferometric Vibrometry (LIV). The first two measurement techniques are extensively in use at the institute ITTM and by other research groups. They are therefore used as a reference for validating the LIV measurement results. An advantage of the LIV technique is that it does not need any seeding of the fluid and that it is non-intrusive. Therefore this measurement technique does not influence the flow, and it can be used in narrow flow passages since there is no blockage, in contrast to probe-based measurement techniques. Further to the measurements, computational simulations were performed with the Fluent® and CFX® codes from ANSYS®, as well as with the in-house code Linars. The Menter SST k-ω turbulence model with the γ-ReΘ transition model was used in order to test its capability to predict the laminar-to-turbulent transition.

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, polarizes the surface and creates a downward moving electro-convective jet. A maximum temperature difference of 1 {\deg}C is measured in the immediate vicinity of the point electrode. Raman spectroscopy on water reveals an enhancement of the vibrational collective modes (3250 $cm^{-1}$) as well as an increase in the local mode (3490 $cm^{-1}$) energy. This bimodal enhancement indicates the spectral changes are not due to temperature. The intense field gradient thus establishes an excited subpopulation of vibrational oscillators far from thermal equilibrium. Delocalization of the collective vibrational mode spatially expands this excited population beyond the microscale. Hindered rotational freedom due to electric field pinning of molecular dipoles retards heat flow and generates a chemical potential gradient. These changes are responsible for the observed changes in refractive index and temperature. It is demonstrated that polar liquids can thus support local non-equilibrium thermodynamic transient states critical to biochemical and environmental processes.

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 permittivity. It is demonstrated that the Bioscope System can indeed measure differences between different substances in aqueous solution and between different concentrations of the same substance in aqueous solution. A qualitative explanation is provided. Possible improvements of the system are suggested.

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 properties of the phenomenon called a ‘floating water bridge’ can be explained by the gradient of Maxwell pressure, replenishing the liquid within the bridge against any drainage mechanism. It is also shown that a number of liquids can form stable and long horizontal bridges. The stability of such a connection, and the asymmetry in mass flow through such bridges caused by the formation of ion clouds in the vicinity of the electrodes, is also discussed by two further experiments.

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 2.5 cm length, this watery connection reveals a number of interesting phenomena currently discussed in water science. Focusing on optical measurement techniques, the flow through the bridge was visualized and data were recorded such as flow velocity and directions, heat production, density fluctuations, pH values, drag force and mass transfer. To provide a better understanding of the basic phenomena involved the discussion references related literature.

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 (stator-rotor), the second step extended the test rig to a one-and-a-half stage configuration (stator-rotor-stator). Measurements were carried out in the transonic test turbine at Graz University of Technology using Particle-Image-Velocimetry and Laser-Doppler-Anemometry. The main results of these experiments are discussed and compared to numerical simulations.

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” positions). Altogether, the measurements downstream of the second stator were performed for ten different clocking positions and upstream of the second stator for two different clocking positions. These different clocking positions have a significant influence on the flow field upstream and downstream of the second stator. Furthermore error estimation and a discussion of the tracer particle response are discussed.

International audience; 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” positions). Altogether, the measurements downstream of the second stator were performed for ten different clocking positions and upstream of the second stator for two different clocking positions. These different clocking positions have a significant influence on the flow field upstream and downstream of the second stator. Furthermore error estimation and a discussion of the tracer particle response are discussed.

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 on a two axis traverse. In flames with forcing the acoustic fluctuations can be extracted from the data by discrimination of all contributions from combustion noise, because it is not correlated with the excitation device. Assuming rotational symmetry of the fluctuations originating from excitation, planar phase-resolved and pseudo-local OH*-chemiluminescence and density fluctuation data is obtained from the measured line-of-sight integrated signals. In the study this technique is applied to a swirl burner configuration with FTFs from known multi-microphone measurements (MMM). In the first step, the externally premixed mode without equivalence ratio fluctuations is studied and in the second step the fuel is injected in the swirler in order to generate equivalence ratio waves. At selected frequencies the planar fields of the OH*-chemiluminescence and density fluctuations are compared to the FTFs in order to improve the understanding regarding the specific amplitude and phase values. In addition to heat release the vibrometer data reveals the periodic oscillation of the conical annular jet of the cold reactants in the combustor filled with hot products. On the global scale the amplitudes and phases of heat release expected from the MMM are satisfactorily reproduced by both methods for the premixed cases, whereas OH*-chemiluminescence data cannot be used as indicator for heat release if equivalence ratio fluctuations are present, because the amplitude of the FTF is significantly over-predicted due to the sensitivity of OH* on the local fuel-air mixture.

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 of the atmospheric model combustion chamber was excited at a frequency around 200Hz. Resonant and non-resonant flame conditions were investigated and compared by laser vibrometer interferometry, schlieren visualization and OH*/CH* chemiluminescence. Additionally, the velocity field was recorded with Particle Image Velocimetry, while the aerodynamics of the burner plenum was analyzed with Computational Fluid Dynamics.Copyright © 2015 by ASME

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 on interferometric techniques the derived signals are path integrals along the measurement beam. To derive local information on the frequency spectra of density fluctuations long-time averaged measurements from each of the two systems were treated using correlation functions and cross spectra. Results were compared to spectral data from a pitot-mounted pressure sensor.

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 second vane row at several different vane-vane positions. Additionally, a fast-response aerodynamic pressure probe was used to get the total pressure distribution downstream of the second vane row for the same positions. Altogether, the measurements were performed for ten different first vane to second vane positions (clocking positions) for measurements downstream of the second vane row and two different clocking positions for measurements upstream of the second vane row. The paper shows that different clocking positions have a significant influence on the flow field downstream of the second vane row. Furthermore, different measurement lines upstream of the second vane row indicate that clocking has nearly no influence on the flow field close to the rotor exit.

The PDA measurements in the downcomer tube of a gas cyclone provide the first in-situ experimental proof of agglomerated particles in a cyclone. The formation of agglomerates in the cyclone explains how particles of less than 20–50 μm are able to settle in the dust bin, in the presence of high velocities. The gas flow in the downcomer tube of the cyclone induces circulation of the particles in the downcomer tube and in the dust bin leading to agglomeration, and thus improves particle separation. The measurements confirm circulation of particles in the dust outlet geometry, as described earlier by Obermair. The particles transported upwards from the dust bin are centrifuged to the wall, and due to the increasing tangential velocities reach the downward flow at the wall. Due to the additional particle separation in the downcomer tube a cyclone with a downcomer tube obtains the best separation efficiency. Further, the measurements prove that due to the dust load there is a change in vortex from a potential vortex to a solid body vortex within the downcomer tube. While the effect of particles on velocity and the associated deceleration of the vortex was well-known in the literature, the change of vortex type had not been observed before.

For one and a half decade, software for interferometric fringe evaluation has been developed and used at Graz University of Technology. Within the framework of an awarded grant, these software packages on interferometric fringe evaluation were subsumed under Windows and Unix platforms and are accessibly under http://optics.tugraz.at . The software focuses on high-resolution digital fringe evaluation including phase stepping, Fourier domain evaluation as well as unwrapping techniques for regular and irregular fringe patterns. For phase objects, Abel-inversion and optical tomography also has been included. New developments on digital holography were taken into account. This paper describes the methods used and focuses on their implementation in such a universal software.

The separation process in a gas cyclone can be divided in three determining steps: (1) the movement of the particles in the cyclone chamber towards the cyclone wall due to centrifugal force, (2) agglomeration of particles at the wall and in the dust bin and (3) separation of the particles and/or agglomerates in the bin. For many years the dust outlet has been considered to be very important for the separation process. However, the actual geometry of the dust outlet was rarely investigated. Tests performed by the authors prove that different dust outlet geometries have significantly different separation efficiencies. Laser Doppler anemometry measurements in a cyclone equipped with three different dust outlet geometries show that both the gas flow in the dust outlet and the gas flow within the lower part of the cyclone change. By examining the different flows within the different dust outlet geometries the influence of the geometry on the separation efficiency can be explained. The best dust outlet of a cyclone is a downcomer tube, due to the “additional” separation process which takes place within it.

The vortex street of a turbine blade profile (VKI-1, 58 mm chord length) was investigated by particle image velocimetry (PIV) and laser vibrometry in a Mach number range between 0.26 and 0.78. While the laser vibrometer (LV) measured the frequency of the density fluctuations in the wake and around the profile, PIV helped to clarify the vortex shedding process. The recordings done by the LV resulted in detailed frequency data of vortex shedding when Mach number and Reynolds number were varied, while the results obtained by PIV enabled a phase resolved measurement of the flow field during vortex shedding.

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.

The aerodynamic behaviour of stator and rotor interaction in axial flow turbines is complex and highly unsteady. Particle image velocimetry (PIV) and laser vibrometry (LV) were used to investigate the phenomena observed in a transonic turbine stage operated continuously in a cold-flow test rig. While LV gave basic information on the frequency behaviour of the density fluctuations in the stator wake, stereoscopic PIV was used for investigations of the flowfield vorticity during rotor blade passing. Phase locking of the vortex shedding to the seventh and eighth harmonics of the blade passing frequency was observed.

In order to investigate the flow field in axial turbine stages, a continuously operating transonic test turbine facility for high pressure ratios was designed at Graz University of Technology, Austria. This test facility allows optical access to the rotor and to the stator trailing edge. The three-dimensional velocity distribution in the region of stator–rotor interaction was investigated by stereoscopic particle image velocimetry. To obtain the three-dimensional velocity vectors in one plane at the mid-section of the turbine blades, a calibration-based method was used. Light-sheet delivery, seeding and triggering to four pre-defined rotor–stator positions are discussed, and an insight into the rotor–stator interaction is given, including vortex shedding in the stator wake.

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-Planck infrared radiation. A number of common solvents can form such bridges as well as low conductivity solutions and colloidal suspensions. The macroscopic behavior is governed by electrohydrodynamics and provides a means of studying fluid flow phenomena without the presence of rigid walls. Prior to the onset of a liquid bridge several important phenomena can be observed including advancing meniscus height (electrowetting), bulk fluid circulation (the Sumoto effect), and the ejection of charged droplets (electrospray). The interaction between surface, polarization, and displacement forces can be directly examined by varying applied voltage and bridge length. The electric field, assisted by gravity, stabilizes the liquid bridge against Rayleigh-Plateau instabilities. Construction of basic apparatus for both vertical and horizontal orientation along with operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

The objective of this work was the application of laser vibrometry as a tool for non-intrusive measurement of frequency spectra in turbulent flows. A laser vibrometer system together with a signal analyser was used to obtain frequency spectra of density fluctuations across a turbulent free jet. Since laser vibrometry is based on interferometric techniques, the derived signals are path integrals along the measurement beam. Frequency spectra recorded in the rotational symmetric flow were then treated using Abel inversion in order to derive information on local density fluctuations. Results for two different flow conditions were compared to spectral data from a constant temperature anemometer and a pitot-mounted pressure sensor.