Michael Breuer

• Univ.-Prof. Dr-Ing. habil.
• Head of Department at Helmut Schmidt University

The objective of this paper is to provide a detailed numerical investigation on the fluid-structure interaction (FSI) test case presented in Kalmbach and Breuer (Journal of Fluids and Structures, 42, (2013), pp. 369-387). It relies on detailed experimental investigations on the fluid flow and the structure deformation using modern optical measureme...

The present paper is concerned with the enhancement of a hybrid LES–URANS method, which enables the simulation of turbulent flows with acceptable computational effort due to a decrease of the resolution requirements for the near-wall region. The unsteady Reynolds-averaged Navier–Stokes (URANS) mode within the hybrid approach is taken into account b...

The paper is concerned with the simulation of particle-laden two-phase flows based on the Euler-Lagrange approach. The methodology developed is driven by two major requirements: (i) the necessity to tackle complex turbulent flows by eddy-resolving schemes such as large-eddy simulation; (ii) the demand to predict dispersed multiphase flows at high m...

The paper is concerned with an efficient partitioned coupling scheme developed for dynamic fluid-structure interaction problems in turbulent flows predicted by eddy-resolving schemes such as large-eddy simulation (LES). To account for the added-mass effect for high density ratios of the fluid to the structure, the semi-implicit scheme guarantees st...

Wall roughness is known to have a significant influence on particle-laden wall-bounded flows directly affecting the particulate and the continuous phase. For sufficiently high mass loading the fluid flow is also indirectly altered by the particles subjected to collisions with rough walls. The paper is concerned with the question how the effect of r...

Laminar–turbulent transition on the suction surface of the LM45.3p blade ( $20\,\%$ thickness) was investigated using wall-resolved large eddy simulation (LES) at a chord Reynolds number of $Re_c=10^6$ and angle of attack $4.6^\circ$ . The effects of anisotropic free stream turbulence (FST) with intensities $TI=0\,\%$ – $7\,\%$ were examined, with...

Aerosol injectors applied in single-particle diffractive imaging experiments demonstrated their potential in efficiently delivering nanoparticles with high density. Continuous optimization of injector design is crucial for achieving high-density particle streams, minimizing background gas, enhancing x-ray interactions, and generating high-quality d...

The paper presents a novel design of a wind gust generator based on an adaptive nozzle for wind tunnel applications and its experimental investigation. The key feature of this design is the movable upper wall of the nozzle, which adjusts the cross-section of the nozzle's outlet. For this purpose, the upper contour of the nozzle is connected to a pr...

The study focuses on fluid–structure interactions (FSI) between a turbulent, gusty fluid flow, and a membrane structure. Lightweight structures are particularly vulnerable to wind gusts and can be completely destroyed by them, making it essential to develop and evaluate numerical simulation methods suited for these types of problems. In this work,...

Aerosol injectors applied in single-particle diffractive imaging experiments demonstrated their potential in efficiently delivering nanoparticles with high density. Continuous optimization of injector design is crucial for achieving high-density particle streams, minimizing background gas, enhancing X-ray interactions, and generating high-quality d...

In the scope of the dtec.bw project hpc.bw, innovative HPC hardware resources were procured to investigate their performance for HSU-relevant compute-intensive software. Benchmarks for different software packages were conducted, and respective results are reported and documented in the following, considering the Intel Xeon architecture used in the...

The paper focuses on fluid–structure interactions (FSI) between a turbulent, gusty fluid flow, and a membrane structure. Lightweight structures are particularly vulnerable to wind gusts and can be completely destroyed by them, making it essential to develop and evaluate numerical simulation methods suited for these types of problems. In this study,...

Armor-piercing fin-stabilized projectiles stand out by their exceptionally high slenderness ratios and ground-level flight at super- and hypersonic speeds. As space constraints limit the integration of measurement equipment into such slender test models, nonintrusive measurement techniques become favorable. The present analysis demonstrates a renew...

Artificial (horizontal) wind gust, wind tunnel experiments, unsteady flow phenomena Abstract In a former study carried out by Wood et al. (2022) and Wood and Breuer (2023) a novel approach for the generation of artificial wind gusts in a wind tunnel setup was presented denoted "the paddle". The device generates wind gusts by dynamically blocking th...

Simultaneously measuring the fluid flow around a flexible structure and the resulting deformations during short-term yet highly dynamic flow events is the focus of this fluid–structure interaction (FSI) study. These scenarios occur when a wind gust impacts a flexible structure, leading to extreme loads and significant deflections. To mimic such gus...

The chaotic and dynamic nature of heat transfer results is either time-consuming or inaccurate predictions of the temperature field in simulations. In particular, the simulation of burning buildings is complex and at the same time the key enabler in saving lives and keeping property damage to a minimum. Deep Learning Neural Networks are a possibili...

The Direct Simulation Monte Carlo (DSMC) method was widely used to simulate low density gas flows with large Knudsen numbers. However, DSMC encounters limitations in the regime of lower Knudsen numbers (Kn < 0.05). In such cases, approaches from classical computational fluid dynamics (CFD) relying on the continuum assumption are preferred, offering...

To generate horizontal wind gusts in a classical wind tunnel, Wood, Breuer, and Neumann [A novel approach for artificially generating horizontal wind gusts based on a movable plate: The paddle,” J. Wind Eng. Ind. Aerodyn. 230, 105170 (2022)] developed a new wind gust generator denoted the “paddle.” The working principle relies on the partial blocki...

The chaotic and dynamic nature of heat transfer results is either time-consuming or inaccurate predictions of the temperature field in simulations. In particular, the simulation of burning buildings is complex and at the same time the key enabler in saving lives and keeping property damage to a minimum. Deep Learning Neural Networks are a possibili...

The paper is a follow-up of the recent study on the assessment of discrete wind gust parameters impacting a flexible lightweight structure as a first step towards the evaluation of the worst-case scenario caused by strong wind gusts (JWEIA 231, 105207, 2022). The present study goes beyond by suggesting an optimization framework which allows to dete...

Wind energy plays a leading role as a renewable energy source, especially in countries with a low annual solar yield.

The evolution of the particle size in turbulent particle-laden flows is a complex phenomenon, which plays an important role in various environmental (e.g., air pollution) and industrial applications (e.g., dry powder inhalers). The main challenge for investigating such flows is the extensive range of length and time scales to be dealt with, especia...

Classical investigations on the aeroelasticity of wings used for the analysis of flutter stability are often carried out based on simplifying model configurations given by elastically mounted rigid wings.

In this study, a recently developed data-driven model for the collision-induced agglomerate breakup (CHERD 195, 2023) is evaluated. It is especially intended for Euler–Lagrange simulations of flows with high mass loadings, where coupled CFD–DEM predictions are too expensive. Therefore, a surrogate model relying on the hard-sphere approach in which...

Computational modeling of the fire‐structure interaction demands the coupling between several models typically implemented in independent simulation software describing distinct physical processes. For instance, in the event of a fire breakout or building on fire, the fire not only increases the temperature of the immediate area but also initiates...

A novel method to generate artificial horizontal wind gusts in a wind tunnel with open test section is presented.

Artificial (horizontal) wind gust, wind tunnel experiments, fluid-structure interaction Künstliche (horizontale) Windböen, Windkanal-Experiment, Fluid-Struktur-Interaktion Abstract The following contribution is based on the study carried out by Wood et al. (2022) dealing with a novel wind gust generator (WGG) used to generate horizontal gusts in a...

The interaction of several instabilities and the influence of free-stream turbulence on laminar-turbulent transition on a 20% thick wind-turbine blade section with a laminar separation bubble (LSB) are investigated with wall-resolved large-eddy simulations (LES). Turbulence intensities (TI) of 0%, 2.2%, 4.5%, 8.6%, and 15.6% at chord Reynolds numbe...

This document reports the operators of the parabolized stability equations (PSE) model employed in the article "Influence of free-stream turbulence on the boundary layer stability of a wind turbine airfoil and near wake". This model was first developed in Nogueira et al. (2022).

Among a few field experiments on wind turbines for analyzing laminar–turbulent boundary layer transition, the results obtained from the DAN-AERO and aerodynamic glove projects provide significant findings. The effect of inflow turbulence on boundary layer transition and the possible transition mechanisms on wind turbine blades are discussed and com...

The paper is concerned with numerical investigations on the effect of vertical wind gusts on airfoils in a parameter range relevant for Micro-Air Vehicles. Using a simplified substitute model instead of an elastic wing, a rigid but elastically mounted airfoil with two degrees of freedom (heave and pitch) is considered. The coupled problem is tackle...

The paper is a step towards the evaluation of the worst-case scenario caused by strong wind gusts impacting civil engineering air-inflated lightweight structures. These extreme events with short durations but high strengths are responsible for short-term highly instantaneous loads endangering the structural integrity of the design. For this purpose...

The paper is concerned with a novel approach to generate horizontal wind gusts in classical wind tunnels. Assuming an open test section of an Eiffel- or Göttingen-type wind tunnel, the new wind gust generator denoted “The Paddle” can be easily retrofitted to such experimental setups at low costs. The device is constructed based on commercially avai...

The literature stresses the inherent stability of laminar pipe flows with parabolic velocity profiles and this paper refers to the relevant publications summarizing this work. To cause such flows to turn into their turbulent state requires laminar pipe flows to be triggered externally. Ring-type, wall-mounted obstacles can be used for this purpose,...

Among a few field experiments on wind turbines for analyzing laminar-turbulent boundary layer transition, the results obtained from the DAN-AERO and aerodynamic Glove projects provide significant findings. The effect of inflow turbulence on the boundary layer transition and the possible transition mechanisms on wind turbine blades are discussed and...

The objective of the present paper is to investigate the transition scenario of the flow around a typical section of a wind turbine blade exposed to different levels of inflow turbulence. A rather low Reynolds number of Rec=105 is studied at a fixed angle of attack but under five different turbulence intensities (TIs) up to TI = 11.2 %. Using wall-...

The present study proposes a novel modeling approach for predicting the wall-impact breakage of agglomerates in wall-bounded particle-laden turbulent flows based on artificial neutral networks (ANN). The suggested model is especially useful for efficient Euler-Lagrange simulation methods relying on the hard-sphere approach and the equivalent-sphere...

The paper addresses the simulation of turbulent wind gusts hitting rigid and flexible structures. The purpose is to show that such kind of complex fluid–structure interaction (FSI) problems can be simulated by high-fidelity numerical techniques with reasonable computational effort. The main ingredients required for this objective are an efficient m...

The impact of a liquid drop on a liquid pool has been widely investigated. The transition regimes between coalescence and splashing of drops include jet formation with single or multiple secondary drops. One of the main features in this regime is the formation of a central liquid jet followed by breakup of the jet in the form of drops. Earlier stud...

The breakage of agglomerates due to wall impact within a turbulent two-phase flow is studied based on a recently developed model which relies on two artificial neural networks (ANNs). The breakup model is intended for the application within an Euler-Lagrange approach using the point-particle assumption. The ANNs were trained based on comprehensive...

The objective of the present paper is to revisit two well-known wind gust injection methods in a consistent manner and to assess their performance based on different application cases. These are the field velocity method (FVM) and the split velocity method (SVM). For this purpose, both methods are consistently derived pointing out the link to the A...

The present paper deals with the modeling of wind gusts within large-eddy simulations (LES). The method relies on a source-term approach and is evaluated based on a simple CFD case and a challenging fluid-structure interaction (FSI) case of a membranous hemisphere in a turbulent boundary layer.

The paper deals with Euler-Lagrange LES of particle-laden flows including efficient models for the breakage of compact dry powder agglomerates due to fluid forces and wall impacts. For the breakup by the fluid stresses theoretical models are used to describe different stress mechanism and the strength of the agglomerate. Concerning the breakage by...

The objective of the present paper is to investigate the transition scenario of the flow around a typical section of a wind turbine blade exposed to different levels of inflow turbulence. As a first step towards this objective, a rather low Reynolds number of Rec = 105 is studied at a fixed angle of attack but under five different turbulence intens...

The outlined analysis validates the dynamic wake meandering (DWM) model based on loads and power production measured at an onshore wind farm with small turbine distances. Special focus is given to the performance of a version of the DWM model that was previously recalibrated at the site. The recalibration is based on measurements from a turbine nac...

The present study completes the development of a model for predicting the effect of wall impacts on agglomerates in turbulent flows. Relying on an Euler-Lagrange hard-sphere approach this physical phenomenon is described in an efficient manner allowing practically relevant multiphase flow simulations at high mass loadings. In a recent study (Khalif...

The outlined analysis validates the dynamic wake meandering (DWM) model based on loads and power production measured at an onshore wind farm with small turbine distances. Special focus is given to the performance of a version of the DWM model that was previously recalibrated at the site. The recalibration is based on measurements from a turbine nac...

The objective of the present paper is to develop a methodology to inject strong wind gusts into the computational domain in order to efficiently simulate their effect on the fluid flow. The design of the methodology based on a source-term formulation takes the feedback effect of the resulting turbulent flow (and, if present, the impacted structure)...

The paper is the numerical counterpart of the experimental investigation on the fluid–structure interaction (FSI) of a wing with two degrees of freedom (DOF), i.e., pitch and heave. Wood et al. (2020) has provided the experimental basis by studying the flutter stability of an elastically mounted straight wing (NACA 0012 airfoil) in a wind tunnel co...

The present paper investigates the fluid–structure interaction (FSI) of a wing with two degrees of freedom (DOF), i.e., pitch and heave, in the transitional Reynolds number regime. This 2-DOF setup marks a classic configuration in aeroelasticity to demonstrate flutter stability of wings. In the past, mainly analytic approaches have been developed t...

The study is concerned with the development of a model for predicting the particle size distribution resulting from the impact of nearly spherical cohesive agglomerates at a wall under a variety of impact conditions. For the derivation of the model an extensive number of discrete element simulations is carried out. The matrix of impact conditions c...

Light detection and ranging (lidar) systems have gained a great importance in today's wake characteristic measurements. The aim of this measurement campaign is to track the wake meandering and in a further step to validate the wind speed deficit in the meandering frame of reference (MFR) and in the fixed frame of reference using nacelle-mounted lid...

The easy-to-shape and light-weight characteristics of membranous structures form the basis of their success in modern civil engineering.

Breakup models were developed for the Euler–Lagrange framework taking breakup by turbulence, drag, and rotation into account. The modeling includes the post breakup treatment and a time lag between successive breakup processes. The prediction of the size distribution based on this four-way coupled Eulerian–Lagrangian approach delivers a reasonable...

Abstract. Light Detection And Ranging (LiDAR) systems have gained a great importance in today's wake characteristic measurements. The aim of this measurement campaign is to track the wake meandering and in a further step to validate the wind speed deficit in the meandering frame of reference (MFR) and in the fixed frame of reference using nacelle m...

The present study is concerned with breakup models for microbubbles in turbulent flows. Analyzing the different physical mechanisms responsible for breakup based on a literature review, breakage due to turbulent fluctuations in the inertial subrange is identified as the most important one. Widely used breakup models for this mechanism are discussed...

Breakup processes of dry powder agglomerates exposed to turbulent flows are investigated based on Euler–Lagrange predictions relying on the large-eddy simulation technique and the hard-sphere method. For this purpose, recently developed breakup models for turbulent, drag and rotary stresses [1] are refined taking relevant time scales of the physica...

Within this study the influence of the interface description for partitioned Fluid-Structure Interaction (FSI) simulations is systematically evaluated. In particular, a Non-Uniform Rational B-Spline (NURBS)-based isogeometric mortar method is elaborated which enables the transfer of fields defined on low-order and isogeometric representations of th...

The present study is concerned with breakup models for agglomerates in turbulent flows. First, a brief literature review is provided describing the state of the art concerning the description and modeling of breakup of agglomerates with special emphasis on the role of fluid forces. That comprises turbulent and drag (inertia) stresses. Furthermore,...

The dimensioning of lightweight structures under wind loads strongly depends on realistic flow conditions. Two different setups have to be distinguished. For a long-term analysis such as dynamic fatigue, temporally and spatially correlated velocity distributions are required as inflow conditions for a large-eddy simulation (LES) to mimic a realisti...

Due to their easy‐to‐shape and light‐weight characteristics, membranous structures are common in modern civil engineering. As all outside buildings they are exposed to wind loads and consequently undergo fluid‐structure interactions (FSI). In order to dimension these membranous constructions and to avoid the damage of the material by FSI, numerical...

Lightweight shell structures have gained significant popularity in the engineering design as they offer high load carrying capacity for low cost. While classical Finite Element models of such structures have been extensively used in practice, the shell formulations for Isogeometric Analysis (IGA), particularly for Kirchhoff‐Love shell structures [1...

The present paper is the numerical counterpart of a recently published experimental investigation by Wood et al. (2018). Both studies aim at the investigation of instantaneous fluid-structure interaction (FSI) phenomena observed for an air-inflated flexible membrane exposed to a turbulent boundary layer, but looking at the coupled system based on d...

The present paper is concerned with numerical investigations on the effect of inflow turbulence on the flow around a SD7003 airfoil. At a Reynolds number Rec = 60,000, an angle of attack α = 4∘ and a low or zero turbulence intensity of the oncoming flow, the flow past the airfoil is known to be dominated by early separation, subsequent transition a...

Thematic Issue on Large-Eddy Simulation

The focus of the present study is on the modeling and simulation of coalescence of surface-tension dominated liquid droplets in a gaseous environment. In the framework of a four-way coupled Euler-Lagrange approach using the large-eddy simulation technique, an improved composite collision outcome model identifying the four regimes of binary collisio...

The present study investigates the fluid­-structure interaction (FSI) of a highly flexible membranous hemisphere immersed into a fully turbulent boundary layer flow. The experiments are carried out in a wind tunnel considering three Reynolds numbers (50,000, 75,000 and 100,000) defined by the diameter of the hemisphere and the free­stream velocity....

The present paper investigates the interaction between a turbulent fluid flow and a flexible membrane structure. Such flexible structures are of increasing interest for modern engineering applications due to their adaptable utilization. Highly flexible membranes under turbulent flow conditions still bare fundamental challenges such as the structura...

The quality of eddy-resolving turbulence simulations strongly depends on appropriate inflow conditions. In most cases they have to be time-dependent and satisfy certain conditions for the first (mean velocities) and second-order moments (Reynolds stresses) as well as concerning suitable length scales. To mimic a physically realistic incoming flow,...

Dry, electrostatically neutral particles in a turbulent flow are a common example for disperse particle–laden flows playing a dominant role in many technical devices such as pulverized coal firing systems or cyclone separators.

Since the development of many flows strongly depends on the inflow conditions, the formulation of feasible conditions at the inlet is a crucial research topic. A procedure such as the precursor simulation is able to deliver appropriate inflow conditions, but this method is limited to simple inflow geometries.

The present paper is concerned with an advanced version of the deterministic coalescence model [1] and its application to turbulent bubble-laden flows. The major drawback of this film drainage model – its incapability to handle large numbers of coalescence processes – is avoided by an a-priori determination of a parametric relation for the transiti...

An efficient technique for the deformation of block-structured grids occurring in simulations of fluid-structure interaction (FSI) problems relying on large-eddy simulation (LES) is proposed. This hybrid approach combines the advantages of the inverse distance weighting (IDW) interpolation with the simplicity and low computational effort of transfi...

The topic of the paper is the development of an enhanced film drainage model for the prediction of bubble coalescence in the context of the Euler–Lagrange approach relying on large-eddy simulations. The starting point is the coalescence model by Jeelani and Hartland (1991), which compared to other often used models has several benefits: (1) A tempo...

In modern civil engineering the application of lightweight membranous structures is growing due to their high grade of spatial flexibility. This raises important issues in order to ensure the safe operation of this type of building such as the response of the flexible structure to wind loads. The present study contributes to this challenging topic...

The Particle-Image Velocimetry (PIV) is a standard optical contactless measurement technique to determine the velocity field of a fluid flow for example around an obstacle such as an airplane wing. Tiny density neutral and light-reflecting particles are added to the otherwise invisible fluid flow. Then two consecutive images (A and B) of a thin las...

The present work introduces an efficient technique for the deformation of block-structured grids occurring in simulations of fluid-structure interaction (FSI) problems relying on large-eddy simulations (LES). The proposed hybrid approach combines the advantages of the inverse distance weighting (IDW) interpolation with the simplicity and low comput...

DFG projects BR 1847/12 and BL 306/26: To simulate practically relevant light-weight structural systems in turbulent flows, a cooperation between the Helmut-Schmidt University Hamburg and the University of Technology Munich was established leading to an original computational methodology based on large-eddy simulation (LES) (Breuer et al., 2012). A...

The present paper addresses the issue of the strong dependency of eddy-resolving simulations for turbulent flows on the employed inflow conditions. Thus, the objective of this study is to analyze the influence of the inflow conditions on the external wall-bounded flow past the SD7003 airfoil and more precisely on the form and size of the laminar se...

The present paper addresses the issue of the strong dependency of eddy–resolving simulations for turbulent flows on the employed inflow conditions. Thus, the objective of this study is to analyze the influence of the inflow conditions on the external wall–bounded flow past the SD7003 airfoil and more precisely on the form and size of the laminar se...

18 helically corrugated tubes with different geometrical configurations for exhaust gas heat exchangers are investigated in this study. Experiments are carried out with air flow on the tube side, cooled by a secondary water flow. The dimensionless corrugation pitch p / d i varies from 0.27 to 1.53, the dimensionless corrugation height e / d i from...

This experimental study is concerned with gas–liquid heat exchangers relying on cross-corrugated tubes. The experiments are carried out with air flow on the inner side of the tube, cooled by a secondary outer water flow. Overall 18 different geometrical configurations are investigated. In contrast to Harleß et al. (2016) the emphasis of the present...

The present study is concerned with the development of a computational model for predicting particle-wall adhesion (deposition) of aerosol particles in turbulent particle-laden flows. Particularly , the standard hard-sphere model is extended to include the adhesion during sticking or sliding particle-wall collisions. For both impact types the depos...

The paper is concerned with the development of a cost-efficient Langevin subgrid-scale model and the analysis of its influence on the dispersed phase of turbulent bubble–laden and particle–laden flows. For this purpose, the Langevin subgrid-scale model of [Pozorski, J., Apte, S. V., 2009. Filtered particle tracking in isotropic turbulence and stoch...

Large-eddy simulations are carried out for the flow past a wall-mounted hemisphere exposed to a thick turbulent boundary layer. To mimic a realistic representation of the incoming velocity distribution, synthetic turbulent fluctuations are introduced upstream of the bluff body by a recently developed source term technique (Schmidt and Breuer, 2016)...

The objective of the present contribution is a complementary investigation on the flow past a wall-mounted hemisphere exposed to a thick turbulent boundary layer. In a first step the flow around a rigid hemispherical obstacle is tackled by detailed wind tunnel measurements based on LDA and wall-resolved large-eddy simulations taking the oncoming tu...

The presentation discusses first steps towards the description of the fluid-structure interaction of a membranous hemisphere in a wind tunnel at a Reynolds number of Re = 50.000 (based on the diameter of the hemispherical model). The highly flexible model is pressurized and submerged into a turbulent boundary layer flow. Particle-image-velocimetry...

This first part of a comprehensive experimental and numerical study investigates the fluid-structure interaction of a wall-mounted flexible hemisphere exposed to a turbulent boundary layer. The Reynolds number of the air flow is set to Re = ρair U∞ D / µair ≈ 50,000, where D is the diameter of the hemisphere. The applied wind tunnel model of the he...

The objective of the present paper is to provide a detailed experimental and numerical investigation on the turbulent flow past a hemispherical obstacle (diameter D). For this purpose, the bluff body is exposed to a thick turbulent boundary layer of the thickness δ = D/2 at Re = 50,000. In the experiment this boundary layer thickness is achieved by...

This paper discusses the findings from a measurement campaign on a rotating wind turbine blade operating in the free atmosphere under realistic conditions. A total of 40 pressure sensors together with an array of 23 usable hot-film sensors (based on constant temperature anemometry) were used to study the behavior of the boundary layer within a spec...

In the present work, the particle agglomeration in turbulent flows is investigated based on an Euler-Lagrange approach relying on the large-eddy simulation technique. In the framework of a hard-sphere model with deterministic collision detection two different models for the agglomeration process of rigid, dry and electrostatically neutral particles...