Christian Oliver Paschereit

Christian Oliver Paschereit
Technische Universität Berlin | TUB · Department of Fluid Dynamics and Technical Acoustics

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729
Publications
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10,306
Citations

Publications

Publications (729)
Article
Full-text available
This paper presents the results of an advanced control strategy that employs active trailing edge flaps to reduce the fatigue loads of an experimental wind turbine. The strategy, called repetitive model predictive control, is a multiple‐input multiple‐output controller that aims at the alleviation of out‐of‐plane blade root bending moments. The str...
Conference Paper
Blending of natural gas with hydrogen is a viable pathway for the decarbonization of industrial gas turbines for combined heat and power applications. Very high blending ratios of hydrogen are needed to achieve significant CO2 emission reductions. However, burning high hydrogen contents in the gas turbine is challenging in terms of NOx emissions an...
Conference Paper
Full-text available
Lean premixed combustion is the state of the art technology to achieve ultra low NO X emissions in stationary gas turbines. However, lean premixed flames are susceptible to thermoacoustic instabilities, lean blowout and flashback. The design of such a combustion system is thus always related to the balancing between the levels of emissions and flam...
Article
Full-text available
This wind tunnel study investigates the aerodynamic effects of mini Gurney flaps (MGFs) and their combination with vortex generators (VGs) on the performance of airfoils and wind turbine rotor blades. VGs are installed on the suction side aiming at stall delay and increased maximum lift. MGFs are thin angle profiles that are attached at the trailin...
Article
Full-text available
Lifting-line based solvers could supersede the blade element momentum (BEM) method as the industry standard in the near future as rotor sizes of modern wind turbines and computational resources continue to increase. A comparison study between both methods is presented where the IEA 10 MW wind turbine is evaluated in the aero-servo-elastic simulatio...
Article
Operation under stable conditions is an important prerequisite for gas turbine safety. While recent studies have focused primarily on acoustic design to avoid thermoacoustic instabilities, in the present study we shift the focus to improving stability margins by flame transfer function (FTF) modification. The flame transfer function of premixed fla...
Article
Full-text available
This study describes the impact of postprocessing methods on the calculated parameters of tip vortices of a wind turbine model when tested using particle image velocimetry (PIV). Several vortex identification methods and differentiation schemes are compared. The chosen methods are based on two components of the velocity field and their derivatives....
Article
Kiel probes have the potential to be a versatile tool for determining stagnation pressure gain in rotating detonation combustors (RDCs), accompanying the commonly used equivalent available pressure method. Although average pressure gain values determined with Kiel probes are comparable to those from thrust stand experiments, one can expect several...
Article
Full-text available
Mitigation of pressure pulsations in the exhaust of a pulse detonation combustor is crucial for operation with a downstream turbine. For this purpose, a device termed the shock divider is designed and investigated. The intention of the divider is to split the leading shock wave into two weaker waves that propagate along separated ducts with differe...
Conference Paper
Full-text available
This study describes the experimental characterization of an RDC across a broad parameter range. The operation and stagnation pressure gain of this device are quantified while varying the air injector area, the fuel injector area, the annulus width, the outlet throat area, the mass flow rate, and the equivalence ratio. It is shown that a reduction...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2022-0278.vid This paper presents the experimental results of an active flap controller on the recently updated Berlin Research Turbine. The three blades of the horizontal axis wind turbine are equipped with active trailing edge flaps. The fatigue load reduction capabilities of a repetitive model p...
Article
Full-text available
In order to determine the flame transfer function of a combustion system, different mechanisms have been identified that need to be modeled. This study focuses on the generation and propagation of one of these mechanisms, namely, the swirl fluctuations downstream of a radial swirl combustor under isothermal conditions. Swirl fluctuations are genera...
Chapter
Pressure gain combustion as an alternative to isobaric combustion has been in the focus of research for the past decades as it potentially allows for increasing the thermal efficiency of conventional gas turbines significantly. Beside the most known concepts, such as pulse detonation and rotation detonation combustors, the shockless explosion combu...
Chapter
Full-text available
The generation of large pressure fluctuations at the combustor outlet due to the periodic combustion process involving propagating detonation waves is a major drawback on the way of integrating a pulse detonation combustor (PDC) into a gas turbine. Recently, the attachment of an annular plenum downstream of a multi-tube PDC was proposed to allow fo...
Conference Paper
Full-text available
Numerical simulations are used here to obtain further understanding on the flashback mechanism of a technically premixed hydrogen flame operated in lean conditions. Recent work from the authors (Mira et al., 2020) showed that the hydrogen momentum strongly influences the flame dynamics and plays a fundamental role on the stability limits of the com...
Preprint
Full-text available
A theoretical idea on how to effectively increase the robust stability of the entire thermoacoustic system through specific modification of the flame transfer function. We apply the Nyquist method, well known in control engineering, to thermoacoustic systems and extend the analysis to account for parameter uncertainties and considerations about rob...
Preprint
Full-text available
This published paper is freely accessible here: https://doi.org/10.5194/wes-7-943-2022 or https://wes.copernicus.org/articles/7/943/2022/
Preprint
Full-text available
This study describes the impact of postprocessing methods on the calculated parameters of tip vortices of a wind turbine model when tested using Particle Image Velocimetry (PIV). Several vortex identification methods and differentiation schemes are compared. The chosen methods are based on two components of the velocity field and its derivatives. T...
Article
Full-text available
The shockless explosion combustion (SEC) is a recently proposed concept aiming for pressure gain combustion through an unsteady process of multiple, distributed autoignitions occurring simultaneously. For this, a stratified fuel profile of dimethyl ether is injected into a continuous air flow. This profile is tailored such that the mixture residenc...
Chapter
The observation of a Hopf bifurcation in fluid dynamics is commonly associated with the occurrence of a global hydrodynamic instability. The increase of a control parameter above a critical value causes a change from a stable to an unstable flow condition. This behaviour is well understood for the occurrence of instabilities in laminar flows. In tu...
Conference Paper
Full-text available
This study explores the increase of stagnation pressure through a detonative combustion process in a rotating detonation combustor (RDC) operating on hydrogen and air. The features of the flow field in an RDC are introduced, as well as the most important length and time scales and how they influence the operating mode of such devices. Through the u...
Article
Full-text available
Emission measurements from unsteady combustion systems such as Pulse Detonation Combustion (PDC) are challenging due to the inherently large variations in pressure, temperature, composition, and flow velocity of the exhaust gas. Comparison of experimental data is additionally complicated by differences in operating conditions and gas sampling setup...
Article
Full-text available
The operation of a multitube pulse detonation combustor (PDC) evokes undesirable pressure fluctuations for a turbine downstream of the combustor. Pressure measurements in a downstream annular plenum reveal distinct pressure fluctuations. Although pressure peaks due to the shock waves emanating from the PDC tubes have been investigated in previous s...
Article
Full-text available
This study describes a rotating detonation combustor (RDC) equipped with a set of nozzle guide vanes (NGVs) of variable number and inclination angle. Different instrumented guide vanes were manufactured and integrated for in situ measurements of static and stagnation pressure. It is shown that the mode progression and stagnation pressure gain of th...
Article
Full-text available
Machine learning and automatized routines for parameter optimization have experienced a surge in development in the past years, mostly caused by the increasing availability of computing capacity. Gradient-free optimization can avoid cumbersome theoretical studies as input parameters are purely adapted based on output data. As no knowledge about the...
Article
Full-text available
The generation and turbulent transport of temporal equivalence ratio fluctuations in a swirl combustor are experimentally investigated and compared to a one-dimensional transport model. These fluctuations are generated by acoustic perturbations at the fuel injector and play a crucial role in the feedback loop leading to thermoacoustic instabilities...
Conference Paper
Machine learning and automatized routines for parameter optimization have experienced a surge in development in the past years, mostly caused by the increasing availability of computing capacity. Gradient-free optimization can avoid cumbersome theoretical studies as input parameters are purely adapted based on output data. As no knowledge about the...
Article
Full-text available
A method is developed to estimate the properties of a global hydrodynamic instability in turbulent flows from measurement data of the limit-cycle oscillations. For this purpose, the flow dynamics is separated into deterministic contributions representing the global mode and a stochastic contribution representing the intrinsic turbulent forcing. Sto...
Conference Paper
Full-text available
Gas turbine combustors are commonly operated with lean premix flames, allowing for high efficiencies and low emissions. These operating conditions are susceptible to thermoacoustic pulsations, originating from acoustic-flame coupling. To reveal this coupling, experiments or simulations of acoustically forced combustion systems are necessary, which...
Conference Paper
Full-text available
In gas turbine combustion systems, the reduction of emissions of harmful combustion by-products is a main development goal. This study provides a methodology to model NOx emissions effectively for varying levels of pilot fuel flows at different operational points. It combines one-dimensional flame simulations using detailed chemistry with a stochas...
Article
Full-text available
The SARS-CoV-2 pandemic has created a great demand for a better understanding of the spread of viruses in indoor environments. A novel measurement system consisting of one portable aerosol-emitting mannequin (emitter) and a number of portable aerosol-absorbing mannequins (recipients) was developed that can measure the spread of aerosols and droplet...
Conference Paper
Modified humid power cycles provide the necessary boundary condition for combustion to operate on a wide fuel spectrum in a steam-rich atmosphere comprising hydrogen and syngas from gasification besides natural gas as fuels. Thus, these cycles with their high efficiency and flexibility fit in a carbon-free energy market dominated by renewable elect...
Conference Paper
In order to determine the flame transfer function of a combustion system only based on isothermal flow field data, three governing mechanisms have been identified which need to be modeled: swirl fluctuations, equivalence fluctuations and velocity fluctuations excited by planar acoustic waves. This study focuses on the generation and propagation of...
Article
Full-text available
Active trailing edge flaps are a promising technology that can potentially enable further increases in wind turbine sizes without the disproportionate increase in loads, thus reducing the cost of wind energy even further. Extreme loads and critical deflections of the blade are design-driving issues that can effectively be reduced by flaps. In this...
Article
Full-text available
The present study examines the possibilities of transferring drag measurement results on reduced-scale train models to the respective full-scale vehicle. A comprehensive experimental and numerical study of the boundary layer and skin friction along trains is performed, focusing on REYNOLDS number effects. The data are supplemented by an extensive l...
Article
Full-text available
An annular plenum is integrated downstream of six pulse detonation combustors arranged in a canannular configuration. The primary purpose of the plenum is the miti-gation of pressure and velocity fluctuations, which is crucial for operation with a downstream turbine. The flow inside the plenum is investigated by means of flush-mounted pressure tran...
Article
Full-text available
This experimental load control study presents results of an active trailing-edge flap feedforward controller for wind turbine applications. The controller input is derived from pressure-based lift estimation methods that rely either on a quasi-steady method, based on a three-hole probe, or on an unsteady method that is based on three selected surfa...
Preprint
Full-text available
Active trailing edge flaps are a promising technology that can potentially enable further increases in wind turbine sizes without the disproportionate increase in loads, thus reducing the cost of wind energy even further. Extreme loads and critical deflections of the blade are design driving issues that can effectively be reduced by flaps. In this...
Article
Full-text available
Accurate and reproducible aeroelastic load calculations are indispensable for designing modern multi-MW wind turbines. They are also essential for assessing the load reduction capabilities of advanced wind turbine control strategies. In this paper, we contribute to this topic by introducing the TUB Controller, an advanced open-source wind turbine c...
Article
Full-text available
An annular plenum is integrated downstream of six pulse detonation combustors arranged in a can-annular configuration. The primary purpose of the plenum is the mitigation of pressure and velocity fluctuations, which is crucial for operation with a downstream turbine. The flow inside the plenum is investigated by means of flush-mounted pressure tran...
Conference Paper
Full-text available
Kiel probes have the potential to be a versatile tool for determining stagnation pressure gain in rotating detonation combustors (RDCs). Although average pressure gain values determined with Kiel probes are comparable to those from thrust stand experiments, one can expect several interferences from the probe in unsteady trans-and supersonic flow. T...
Article
Low calorific value (LCV) gaseous fuels are generated as by-products in many commercial sectors. Their efficient exploitation can be a considerable source of primary energy. Typically, product gases from biomass are characterized by low lower heating values (LHV) due to their high concentration of inert gases and steam. At the same time, their comp...
Conference Paper
Vortex generators (VGs) are often used to optimize the flow on wind turbine rotor blades, enhancing the annual energy production between 1-3% with particular focus on the underperforming aerodynamics in the blades root zone. This has generated great interest among the scientific community, proposing new geometries, besides the common rectangular an...
Article
Full-text available
Wind Energy is substantially growing in recent years and is now one of the most competitive renewable energy sources on the market. To further foster the growth of this energy source, increasing effort is put into building accurate numerical models. Most models compute the loads acting on the turbine as a dependence of some sort to the angle of att...
Book
Modified humid power cycles provide the necessary boundary condition for combustion to operate on a wide fuel spectrum in a steam-rich atmosphere comprising hydrogen and syngas from gasification besides natural gas as fuels. Thus, these cycles with their high efficiency and flexibility fit in a carbon-free energy market dominated by renewable elect...
Article
Full-text available
In this paper, a method to determine the angle of attack on a wind turbine rotor blade using a chordwise pressure distribution measurement was applied. The approach used a reduced number of pressure tap data located close to the blade leading edge. The results were compared with the measurements from three external probes mounted on the blade at di...
Article
Shockless explosion combustor (SEC) is a promising concept for implementing pressure gain combustion into a conventional gas turbine cycle. This concept aims for a quasi-homogeneous autoignition that induces a moderate rise in pressure. Since the ignition is not triggered by an external source but driven by chemical kinetics only, the homogeneity o...
Article
Full-text available
This paper investigates the aerodynamic impact of Gurney flaps on a research wind turbine of the Hermann-Föttinger Institute at the Technische Universität Berlin. The rotor radius is 1.5 m, and the blade configurations consist of the clean and the tripped baseline cases, emulating the effects of forced leading-edge transition. The wind tunnel exper...
Article
Any outlet restriction downstream of Pressure Gain Combustion (PGC), such as turbine blades, affects its flow field and may cause additional thermodynamic losses. The unsteadiness in the form of pressure, temperature and velocity vector fluctuations has a negative impact on the operation of conventional turbines. Additionally, experimental measurem...
Article
Full-text available
A joint experimental and numerical investigation of turbulent flame anchoring at externally heated walls is presented. The phenomenon has primarily been studied for laminar flames and micro-combustion while this study focuses on large-scale applications and elevated Reynolds number flows. Therefore, a novel burner design is developed and examined f...
Article
Full-text available
The reduction of NOx emissions remains a driving factor in the design process of swirl-stabilized combustion systems, to meet legislative restrictions. In reacting swirl flows, hydrodynamic coherent structures, such as periodic large-scale vortices in the shear layer, induce zones with increased heat release rate fluctuations in connection with tem...
Article
Full-text available
Using steam as heat carrier and working media has merits to increase electric efficiency up to 60% and decrease NOx emission to single-digit compared to dry gas turbine cycles. These attribute to the physical properties of steam as having high heat capacity to reduce local flame temperature, and hence reduce emissions by inhibiting thermal NOx forw...
Article
Power augmentation devices in wind energy applications have been receiving increasing interest from both the scientific and the industrial community. In particular, Gurney Flaps (GFs) showed a great potential thanks to the passive functioning, the simple construction and the possibility to add them as a retrofit to existing rotors. Within this cont...
Article
A novel modeling strategy is proposed which allows high-accuracy predictions of aerodynamic and aeroacoustic target values for a low-pressure axial fan, equipped with serrated leading edges. Inspired by machine learning processes, the sampling of the experimental space is realized by use of a Latin hypercube design plus a factorial design, providin...
Article
Full-text available
The flame transfer functions (FTF) is a key quantity to assess the thermoacoustic properties of combus- tion systems. It is known to depend on the hydrodynamic instabilities of the combustor flow. This work investigates how the FTF is affected by a global flow instability known as the precessing vortex core (PVC) which is often observed in swirl fl...