Bernd Leitl

Bernd Leitl
Hamburg University | UHH · Meteorologisches Institut (MI)

PhD

About

149
Publications
23,507
Reads
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1,834
Citations
Additional affiliations
January 1995 - February 1997
Colorado State University
Position
  • Lynen Research Fellow of the Alexander von Humboldt Foundation

Publications

Publications (149)
Article
We present a methodology and the first tests to estimate the settling velocity of airborne microplastics based on wind tunnel experiments. A novel approach and original perspective are proposed, discussing in detail challenges and faced problems, both on the theoretical and experimental sides. Several experiments were performed, releasing fragments...
Chapter
Multiperspektivische Blicke auf ein Jahrhundert Gelehrsamkeit. Anlass für diese mehrbändige Publikation, die sich der Komplexität von Universität multiperspektivisch nähert, sind 100 Jahre Hamburger Universitätsgeschichte. Nach Band 1 zu allgemeinen Aspekten und Entwicklungen (2020) enthalten die Bände 2 (2021), 3 (2022) und 4 (2023) Beiträge zu ei...
Article
Full-text available
Solving the hydrodynamical equations in urban canopies often requires substantial computational resources. This is especially the case when tackling urban wind comfort issues. In this article, a novel and efficient technique for predicting wind velocity is discussed. Reynolds-averaged Navier–Stokes (RANS) simulations of the Michaelstadt wind tunnel...
Article
In the present work, measurements of the atmospheric boundary layer (ABL) flow, reproduced in a boundary layer wind tunnel, and large eddy simulation (LES) of the full scale ABL are presented for two ground roughness lengths. In the numerical part the ABL is simulated by utilizing the cyclic boundary conditions in downstream direction and artificia...
Conference Paper
The Association of German Engineers (VDI) published in Dez. 2000 the guideline VDI 3783 Part 12 "Application of wind tunnels" and focuses on physical modelling of flow and dispersion processes in the atmospheric boundary layer. The guideline has now been revised and the new edition draft will be published this year. The guideline was adapted to the...
Article
Full-text available
Motivated by a limited understanding of how valleys affect near-surface turbulence, characterizations of neutrally stable atmospheric-boundary-layer flows over isolated valleys are presented. In particular, the influence of the slopes of the three-dimensional ridges that form the idealized valleys are investigated. Flows over three distinct symmetr...
Article
Full-text available
With the aim of ascertaining the effects of the widths ("A" ) of valleys on near-surface turbulence, flows over an isolated symmetric three-dimensional valley of constant depth ("H" ) and slopes are characterized in a large boundary layer wind tunnel. Starting at A = 4H, valley widths were systematically varied to A = 12H with constant increments o...
Poster
Full-text available
Large Eddy Simulations (LES) are of raising interest for numerous engineering applications in which an accurate flow prediction is necessary. This paper searches for the optimum mesh resolution in numerical simulations reliably predicting dispersion of pollutants in the lower part of the Atmospheric Boundary Layer (ABL). For the dispersion of pollu...
Conference Paper
Full-text available
Large Eddy Simulations (LES) are of raising interest for numerous engineering applications in which an accurate flow prediction is necessary. This paper searches for the optimum mesh resolution in numerical simulations reliably predicting dispersion of pollutants in the lower part of the Atmospheric Boundary Layer (ABL). For the dispersion of pollu...
Article
Full-text available
We demonstrate the capability of the PALM model system version 6.0 to simulate neutrally stratified urban boundary layers. Our simulation uses the real-world building configuration of the HafenCity area in Hamburg, Germany. Using PALM's virtual measurement module, we compare simulation results to wind-tunnel measurements of a downscaled replica of...
Article
Full-text available
Ziel des BMBF-Programms "Stadtklima im Wandel" war die Entwicklung, Validierung und Anwendung eines gebäudeauflösenden Stadtklimamodells für ganze Städte. Das Verbundprojekt 3DO übernahm die dem Modul B zugeordneten Forschungsaufgaben: Aufbereitung vorhandener Daten aus der Langzeitbeobachtung (LTO), Aufbau neuer Messstationen, Gewinnung neuer drei...
Article
Gefahrstofffreisetzungen aus technischen Anlagen können erhebliche Risiken für Mensch und Umwelt bergen und sind deshalb bei der Planung, der Genehmigung und im Regelbetrieb technischer Anlagen zu berücksichtigen. Zur Identifizierung von Gefahrenbereichen im Zusammenhang mit Gasfreisetzungen und zur Bewertung der Wirksamkeit von Schutzmaßnahmen wer...
Preprint
Full-text available
We present the capability of PALM 6.0, the latest version of the PALM model system, to simulate neutrally stratified urban boundary layers. The studied situation includes a real-case building setup of the HafenCity area in Hamburg, Germany. Simulation results are validated against wind-tunnel measurements of the same building layout utilizing PALM'...
Article
This work investigates the release and dispersion of volatile organic hydrocarbons, which may escape from external floating roof tanks (EFRT) during normal operation or in case of damage. The dispersion will be described using CFD simulations in close range of the EFRT where hazardous areas are assigned. The aim of this work is to investigate which...
Article
Full-text available
To cope with weather and climate-induced impacts as well as with air pollution in cities, the German research programme “Urban Climate Under Change” ([UC]2) aims at developing, testing and validating a new urban climate model, which is able to cover the full range of temporal and spatial scales of urban atmospheric processes. The project “Three-dim...
Article
Full-text available
The local climate in cities differs from the one in rural areas, most prominently characterized by increased surface and air temperatures, known as the “(surface) urban heat island”. As climate has changed and continues to change in all areas of the world, the question arises whether the effects that are noticeable in urban areas are “homemade”, or...
Article
Full-text available
Essential prerequisites for a thorough model evaluation are the availability of problem-specific, quality-controlled reference data and the use of model-specific comparison methods. The work presented here is motivated by the striking lack of proportion between the increasing use of large-eddy simulation (LES) as a standard technique in micro-meteo...
Article
Full-text available
Time-dependent three-dimensional numerical simulations such as large-eddy simulation (LES) play an important role in fundamental research and practical applications in meteorology and wind engineering. Whether these simulations provide a sufficiently accurate picture of the time-dependent structure of the flow, however, is often not determined in e...
Article
One of the key issues of recent research on the dispersion inside complex urban environments is the ability to predict individual exposure (maximum dosages) of an airborne material which is released continuously from a point source. The present work addresses the question whether the computational fluid dynamics (CFD)–Reynolds-averaged Navier–Stoke...
Article
Full-text available
This is the review of CFD (Computational Fluid Dynamics) guidelines for dispersion modeling in the USA, Japan and Germany. Most parts of this review are based on the short report of the special meeting on CFD Guidelines held at the International Symposium on Computational Wind Engineering (CWE2014), University of Hamburg, June 2014. The objective o...
Conference Paper
First responders need a more or less instant estimate of danger zones resulting from accidental airborne releases of hazardous materials in order to take immediate action, to coordinate rescue teams and to protect the population and critical infrastructure. To fulfill the need for efficient access to reliable results in a first responders environme...
Chapter
Caused by synoptic changes and the diurnal cycle, the atmospheric boundary layer is never steady state. The unsteadiness is especially pronounced within and above the urban canopy layer. In former times, it was not possible to take the natural variability of the urban atmosphere properly into account, due to a lack of both computer power for models...
Article
Full-text available
This is the review of CFD guidelines for dispersion modeling in US, Japan and Germany. Most parts of this review are based on the short report of the special meeting on CFD Guidelines held at the International Symposium on Computational Wind Engineering (CWE2014), Hamburg University, June 2014. The objective of this meeting was to introduce and dis...
Article
Accidental and deliberate releases of harmful substances pose a tremendous challenge to first responders because of the large number of possible casualties and the resulting potential environmental and economic damage in densely populated areas. Within minutes after a release, countermeasures must be taken to protect the population and environment...
Article
Atmospheric transport models are in use to model the airborne transport of toxic or radioactive gases or aerosols in large, regional or very local scale events. Different approaches are available, ranging from simple parametric models and Gaussian methods to Lagrangian dispersion models and advanced CFD-based modelling suites. The variety of the mo...
Chapter
A main research task of COST Action ES1006 is the evaluation of atmospheric dispersion models by their comparison against test data from qualified field and laboratory experiments and by a model inter-comparison. The model comparison and evaluation carried out for three test cases is presented, addressing the performance of the different modelling...
Conference Paper
Full-text available
The aim of this wind tunnel study is to identify limitations in boundary layer wind flow modeling over large-scale complex terrain. As reference site, the Alaiz mountain range near Pamplona in northern Spain was chosen. Throughout the project, a number of experimental challenges were identified and investigated systematically. For example, a specif...
Article
Full-text available
The capability to predict short-term maximum individual exposure is very important for several applications including, for example, deliberate/accidental release of hazardous substances, odour fluctuations or material flammability level exceedance. Recently, authors have proposed a simple approach relating maximum individual exposure to parameters...
Article
A set of parameters is introduced to characterize the dispersion of puff releases based on the measured dosage. These parameters are the dosage, peak concentration, arrival time, peak time, leaving time, ascent time, descent time and duration. Dimensionless numbers for the scaling of the parameters are derived from dimensional analysis. The dimensi...
Article
Full-text available
A model wind turbine has been designed at the University of Hamburg within the scope of the FP7 fundend project WAUDIT. The purpose of the experiment described in this paper is to characterize the performances of two rotors by means of measuring the thrust coefficient Ct. Ct is a similarity parameter for the wake and is thought to be the most effec...
Conference Paper
Full-text available
Rescue services apply numerical models in emergency situations involving accidental gas releases in urban environments. These models are often validated according to air quality standards. However in case of emergency situations the required information is very different from the results of an air quality study. Probabilities of high concentrations...
Conference Paper
Full-text available
Testing and evaluating available models by model inter-comparison, as well as by comparison against test data from qualified field and laboratory experiments is a main research task of COST Action ES1006. Assuming that a typical emergency response model has already been validated with regard to local-scale dispersion modelling, the existing model e...
Conference Paper
Full-text available
The renewed concern and increasing need in assessing risks and consequences from local-scale technological hazards and disaster events in complex built-up environments gave computational tools a unique value for emergency response management and large efforts have been taken in the development of different types of numerical tools able to address i...
Conference Paper
Full-text available
Updates on the results from COST Action ES1006 activity are presented and discussed. The main focus of the ES1006 Action is the evaluation of the airborne pollutant dispersion models, when applied for accidental or intentional releases in complex built environments, urban or industrial. The main achieved outcomes are introduced and briefly illustra...
Article
Full-text available
The COST Action ES1006 is mainly aimed at evaluating and improving the reliability of neighbourhood-scale emergency response tools on the basis of a comprehensive, concerted and harmonized cross-national approach. The main focus is the evaluation of the air dispersion models, when used in urban or industrial environments with complex building struc...
Chapter
The first results of a model validation test case, carried out in the research context of the COST ES1006 Action, are outlined and discussed. The validation exercise was established with an application-oriented approach, devoted to the investigation of the modeling performances in the emergency-response framework.
Article
Full-text available
We have developed a local-scale high-resolution atmospheric dispersion model using large-eddy simulation (LOHDIM-LES) to assess the safety at nuclear facilities and to respond to emergency situations resulting from accidental or deliberate releases of radioactive materials (e.g., a terrorist attack in an urban area). In Part 1, the unsteady behavio...
Chapter
The turbulent dispersion process responsible of the VOCs transport within and above the canopy is still under study. This issue is of great interest since VOCs contribute to the global chemical reactions encountered into the troposphere. At the forest scale, VOCs are expected to travel within and above the forest, interacting with each other or wit...
Conference Paper
Full-text available
The paper will summarize and discuss the process of analyzing met data and numerical simulation results and tries to document a recommended strategy for deciding on the bounds of a large area terrain model not only based on geometrical but also on meteorological constraints. In the given example, the boundary conditions for the wind tunnel model we...
Conference Paper
Full-text available
In this paper, a methodology using a modelled emission source and corresponding concentration measurements and its application for the evaluation of ventilation in urban areas are described.
Article
Urban flow fields computed by two steady Computational Fluid Dynamics models based on the Reynolds-averaged Navier Stokes equations (CFD-RANS) are compared to validation data measured in a boundary-layer wind-tunnel experiment. The numerical simulations were performed with the research code ADREA and the commercial code STAR-CD. Turbulent flow with...
Conference Paper
First responders need a more or less instant estimate of danger zones resulting from accidentally released hazardous materials in order to take immediate action, to coordinate rescue teams and to protect human population and critical infrastructure. To fulfill the need for a sufficient dispersion modeling accuracy while maintaining efficient access...
Conference Paper
The description of atmospheric turbulence in densely built urban environments is a major theoretical challenge, which has wide-ranging practical implications - regarding for example pollutant dispersion, wind comfort, and many other micro-climatic issues. The traditional approach to adopt obstacle-resolving micro-scale meteorological models based o...
Article
IntroductionTypes of CFD ModelsValidation DataWind Tunnel ExperimentsSummaryReferences
Article
Full-text available
Releases of hazardous agents in complex built environments pose a tremendous challenge to emergency first responders and authorities in charge, due to the large number of casualties potentially involved and to possible the damages to ecosystems and infrastructures. Air motions in built-up areas are very complex and adequate modelling tools have to...
Chapter
Flow over complex terrain and hills is a concern in many research areas such as determination of air pollution zones, predictions of smoke movement from forest fires, wind energy assessment and siting of wind energy converting systems (WECS). It can be examined by means of field studies, theoretical analysis, wind tunnel simulation and numerical mo...
Chapter
Over the last fifteen years a substantial increase in the use of wind energy can be monitored. Presently, several wind farms are planned or under construction in which many wind turbines are arranged as grids. A successful design of a wind farm relies on a number of issues such as: the prediction of wind resource, the rotor-blade design and the opt...
Conference Paper
First responders need a more or less instant estimate of danger zones resulting from accidentally released hazardous materials in order to take immediate action, to coordinate rescue teams and to protect human population and critical infrastructure. To fulfil the need for a sufficient dispersion modelling accuracy while maintaining efficient access...
Conference Paper
Validating LES-based flow and dispersion models for the purpose of predicting transient flow and dispersion phenomena is more demanding than validating RANS-based codes. Since the model output is no longer related to stationary or quasi-stationary boundary conditions, and since the model results are not restricted to mean flow and average dispersio...
Article
Full-text available
The regular obstacle array of the Mock Urban Setting Test (MUST) field site in the Utah West Desert has been replicated in the large boundary layer wind tunnel at Hamburg University. Dispersion from a point source within an idealised urban canopy for an oblique wind direction was a main focus of the wind tunnel measurements. Two different methods w...
Article
Methods of eddy structure identification are applied to velocity data of atmospheric surface layer flows modeled in a boundary-layer wind tunnel. The objective is to test their potential to serve as mathematical tools for the validation of eddy-resolving numerical models like large-eddy simulation and for the generation of realistic turbulent inflo...
Article
Full-text available
The paper describes difficulties in the proper evaluation of obstacle-resolving urban CFD models. After a brief description of the evaluation methodology suggested by the European COST action 732, focus is laid on the question of how to obtain validation data that can be regarded as a reliable standard. Data from an entire year of measurements at a...
Article
Validating LES-based flow and dispersion models for the purpose of predicting transient flow and dispersion phenomena is more demanding than validating RANS-based codes. Since the model output is no longer related to stationary or quasi-stationary boundary conditions, and since the model results are not meant to be used for predicting mean flow and...