E-Mail: hasangaz(at)b-tu.de

Betreuer:

Prof. Dr. -Ing. Christoph Egbers

Titel der Dissertation:

Flow control of a flat plate turbulent boundary layer flow through micro blowing under stochastic forcing (Arbeitstitel)

Beschreibung:

Turbulence in wall bounded flow has been and still an extensively investigated flow field where its implication in engineering applications such as high performance aerofoil and turbine blades, scaling in classical boundary layer theory is  partly accountable to a large section of unanswered questions. Yet, amount of information received about its control is scarcely filling up the gap to a successive flo control method development. Within the scope of this Ph.D., one of the active control method as Micro-blowing is investigated experimentally to obtain measurement data within the range of moderate Reynolds number (Reynolds number based on momentum thickness and local free stream velocity upto 4000). Most of the experiments performed on application of Navier Stokes equation discerns only to the dynamics of classical boundary condition, where as with the developing design engineering necessitates further effort on flow control mechanism. Several studies has shown that skin friction drag constitutes a large portion of the total drag contribution, considering drag reduction as result, blowing applied vertically from a porous surface induces momentum to the turbulent boundary layer and its influence is measured using optical measurement techniques such as Laser Doppler Velocimetry and Particle Image Velocimetry. Conventional modelling of boundary layer states different scales of structures, their interaction becomes increasingly important in outer region where the flow is primarily dominated by the large scale and very large scale motion. In particular, energy dissipation from inner to outer region of the boundary layer is an outcome of constantly injected momentum. Thus application of the stochastic analysis to the acquired data exhibit induced turbulence  simultaneously with changing mean properties of the flow. Instantaneous velocity data interpreted as spectral and statistical form to derivate an empirical model with increasing Reynolds number.

Kurz-Vita:

Gazi Hasanuzzaman was born in Dhaka, the capital of Bangladesh in the year of 1984. He has completed his bachelor studies with a major in aerodynamics from the discipline of Mechanical engineering from Military Institute of Science and Technology. Later, he studied Power Engineering from Brandenburg University of Technology and successfully completed his degree in the year of 2015. His master thesis was directed in the field of wind tunnel experiment and numerical simulation for an efficient duct design for building integrated wind turbines.  During October of 2016, he started working for his Ph.D. from the Department of Aerodynamics and Fluid Mechanics under supervision of Prof. Dr.-Ing. Christoph Egbers.

E-Mail: muralaru(at)b-tu.de

Betreuer:

Prof. Dr.-Ing. Ulrich Riebel
Prof. Dr.-Ing. Heiko Schmidt/Dr. Moritz Fragner

Titel der Dissertation:

Flow, heat transfer, noxious gas and particle separation in non-isothermal wet electrostatic separators in the field of bio-energy technology: Basic investigations on the electrohydrodynamic flow stability (Arbeitstitel)

Beschreibung:

In electrostatic precipitators, turbulent flow states are observed, which are not due to high Reynolds numbers, but due to electrohydrodynamic (EHD) instability of the flow. In order to model the physically well-founded thermal and mass transfer, the statistical parameters of the EHD flow must be known. ODT (One Dimensional Turbulence) is a novel approach for flow modeling that can provide this statistical information.

The aim of the dissertation is to observe and quantitatively investigate the occurrence of intermixing processes in model experiments on electrically charged, unstably stratified aerosols. From the measurements suitable statistical parameters (average, standard deviation, power density spectra) are to be derived for a quantitative description. Based on these parameters, the statements of the ODT approach are to be verified and, if necessary, quantified.

In order to implement a functioning design model for the novel non-isothermal ESPs, a further development of the ODT algorithms with a view to the consideration of the EHD-driven devices is required and an experimental review of this model approach can be achieved by modeling lab scale experiments. In the laboratory experiments, the flows are preferably visualized by fluorescence or LIF methods.

Kurz-Vita:

E-Mail: radow(at)b-tu.de

Betreuer:

Prof. Dr. Michael Breuß

Titel der Dissertation:

Geometrische Optimierung / Geometric Optimisation (Arbeitstitel)

Beschreibung:

Algorithms based on L1 regularisation have proven very successful over the past years. While they can achieve competitive results in multiple fields, they are often difficult to handle. The main interests of the research project are optical flow and acoustic source characterisation. The goal is to derive and investigate models as well as to develop fast and efficient algorithms for the aforementioned and related tasks.

Kurz-Vita:

Georg Radow received the Masters degree in Applied Mathematics in 2015 from Brandenburg Technical University Cottbus-Senftenberg, where he is a member of the applied mathematics group since 2015. He is interested in applications of optimisation, especially those in the fields of image denoising, computer vision and acoustic engineering.

E-Mail: Rakhi.Rakhi(at)b-tu.de

Betreuer:

Prof. Dr.-Ing. Heiko Schmidt

Titel der Dissertation:

Stochastic modeling of turbulent flow (Arbeitstitel)

Beschreibung:

The purpose of the project is to apply ODT and ODTLES for a flat plate turbulent boundary layer (FPTBL) with blowing and an electrohydrodynamical configuration.  The results will first be compared to DNS and spatially developing ODT results. Then the boundary conditions will be adapted to the conditions used in the experimental FPTBL configuration and results will finally be compared with the experimental ones.

Kurz-Vita:

I completed my B.Sc. in Physics with an honours degree from Miranda House, University of Delhi. Later, I pursued M.Tech. in Nuclear Science and Technology from Department of Physics and Astrophysics, University of Delhi, India. I completed my Master's in 2016 having carried out my Master's Thesis from Indira Gandhi Centre for Atomic Rsearch (IGCAR), Kalpakkam, India. My Master's Thesis was based on 'CFD investigation of heat transfer enhancement using multi-tray core catcher in SFR'. Apart from  the thesis, I carried out numerous internships during the course to gain hand-on experience and developed interest in the field of CFD and fluid flow. This motivated me to pursue further research in the field of Fluid flow. Presently, I am enrolled as a Research Scholar in the Mechanical engineering department of  BTU, Cottbus. I work on 'Stochastic modelling of turbulent flow'. I am determined to complete the task at hand and am ready to work hard to achieve my aim of becoming a successful researcher.

E-mail: Sparsh.Sharma(at)b-tu.de

Betreuer:

Ennes Sarradj

Prof. Dr.-Ing. Heiko Schmidt

Titel der Dissertation:

Stochastic Modelling of Leading Edge Noise (Arbeitstitel)

Beschreibung:

The acoustic signature from an airfoil downstream an incoming turbulent flow is a complex mathematical phenomenon which requires solving the nonlinear governing equations with higher resolutions. The aerodynamic noise arises because of two different phenomena. The first one is the impulsive noise, which is a result of moving surface or surfaces in nonuniform flow conditions. The displacement effect of an immersed body in motion and the unsteady aerodynamic loads on the body surface generate pressure fluctuations that are radiated as sound. This kind of noise is deterministic and relatively easy to extract from aerodynamic simulations because the required resolution in space and time to predict the acoustics is like the demands from the aerodynamic computations. If the surfaces move at speeds comparable to the speed of sound or there is an interaction between a rotor and a stator wake, these tonal noise components can be dominant.

The other noise mechanism is the result of turbulence and therefore arises in nearly every engineering application. Turbulence is, by its very nature, stochastic, and therefore has a broad frequency spectrum. Turbulent energy is converted into acoustic energy most efficiently near sharp edges. By the definition, an unsteady flow is one where the flow field variables at any point are changing with time which means all the aerodynamic parameters fluctuate with time too and are certainly the inhibitors of all the disturbances which causes the generation of noise from an airfoil. As stated, turbulence noise exists almost every time, consequently, aerodynamic noise is usually a broadband noise sometimes augmented by narrow tonal components coming from impulsive noise sources. 

Kurz-Vita:

Born and raised in New Delhi, India, Sparsh has developed a passion for Aircraft since his early childhood. Before graduating with a MSc in Computational Aerodynamics from Moscow Institute of Physics and Technology (Moscow, Russian Federation), he was a research fellow at the Indian Institute of Technology Madras (Chennai, India) and Indian Institute of Technology Kanpur (Kanpur, India) where he developed a tool for sonic boom propagation through the atmosphere. During his masters, he got an opportunity to work on Shock waves minimization with the team who designed the iconic Sukhoi 27 fighter aircraft. Currently, he is working on the methods to predict the acoustic radiation stochastically from a body immersed in a turbulent flow field. Besides this, he enjoys flying UAVs, travelling and cricket.

E-Mail: Markus.Strehlau(at)b-tu.de

Betreuer:

Prof. Dr. Carsten Hartmann

Titel der Dissertation:

Robuste stochastische Modellierung komplexer getriebener Systeme (Arbeitstitel)

Beschreibung:

Ein Leitmotiv des Promotionsprojekts wird die Frage sein, inwieweit sich effektive Modele zur Steuerung und Vorhersage komplexer Systeme eignen. Zur Untersuchung dieser Frage sollen klassische Modell- oder Dimensionsreduktionsverfahren für (deterministische) komplexe Systeme mit neuartigen statistischen und informationstheoretischen Methoden, wie der entropie-basierten Sensitivitätsanalyse verbunden werden. Konkret sollen innerhalb des Projekts Modell- und Dimensionsreduktion unter zwei verschiedenen Gesichtspunkten betrachtet werden:

1. Effektive Modelle für Intermittenz und Modellreduktion von stochastischen Prozessen unter Berücksichtigung des Antwortverhaltens gegenüber zeitabhängigen Störungen.

2. Rückwartsstabilität von effektiven Modellen für die optimale Regelung und optimales Sampling von transienten Moden in getriebenen Nichtgleichgewichtssystemen. Geplant ist zudem, die theoretischen Resultate des Projekts anhand geeigneter experimenteller Daten zu validieren, wobei insbesondere die Varianzdaten aus den rotierenden Scherströmungsexperimenten (Harlander) sowie Partikelmessdaten aus der mechanischen Verfahrenstechnik (Riebel) infrage kommen.

Kurz-Vita:

Ich habe an der Universität zu Köln Physik studiert und in Potsdam am Albert Einstein Institut meine Masterarbeit auf dem Gebiet der numerischen Relativitätstheorie geschrieben. Nun möchte ich an der B-TU Cottbus-Senftenberg auf dem Gebiet der Statistik und Wahrscheinlichkeitstheorie lernen und dazu beitragen, wie Modelle von hochdimensionalen getriebenen Systemen reduziert werden, um sie numerisch und analytisch besser zugänglich machen zu können.

E-mail: Wenchao.Xu(at)b-tu.de

Betreuer:

apl. Prof. Dr. rer. nat. habil. Uwe Harlander

Titel der Dissertation:

Stochastic dynamics of homogeneous and stratified rotating shear flows (Arbeitstitel)

Beschreibung:

Most shear flows show turbulence although they do not have unstable modes. This happens, for example, in the plane Couette flow and the Poiseuille tube flow. This phenomenon is called "non-modal instability". Shortly, the theory works as follows: The stability of shear flows is verified by the linear Orr-Sommerfeld equation. It is found that, even in the case of purely real (i.e. stable) eigenvalues, a temporally limited transient growth is possible if the system matrix is not symmetrical, which is almost always the case with shear flows.

This mechanism has been investigated and verified with many examples. Perhaps the most impressive examples come from meteorology, where it has been shown that devastating storms raised over the non-modal instability (Mackenzie, 2003). However, an important aspect of non-modal instability was seldom investigated: the occurrence of very high variability in stable shear flows with stochastic forcing. One would think that a stochastically forced stable shear flow has a variance corresponding to stochastic forcing. In the case of flows with non-symmetrical system matrices, however, a variance can be many times higher than the forcing (Farrell, 1993). This is because the stochastic forcing can be coincident with non-modally growing disturbances. The non-modal growth generates disturbance amplitudes in a short time, which increase nonlinear interactions and thus the variance. The aim of the research is to experimentally prove that shear currents can show a high variability due to non-modal growth. For this purpose, reference experiments are planned to examine the existing theories.

Kurz-Vita:

Wenchao Xu is currently a PhD student of the Department of Aerodynamic and Fluid Mechanics in Faculty of Mechanical Engineering, Electrical and Energy Systems. He was born in Shandong, China and finished his Bachelor Degree of the major Thermodynamic Engineering in Shanghai University of Electric Power in 2010. After one year, he came to Germany and continued his study in Dresden University of Technology. In 2013, he served as intern in the Power Generation Division of Siemens AG, where he found his interest in fluid dynamics and decided to concentrate his study in this field. After the internship, he worked in Helmholtz-Zentrum Dresden-Rossendorf and performed large eddy simulations of stratified counter-current steam/water flow. In 2015, he finished his Master thesis with the theme large eddy simulation on an axial compressor cascade with tip clearance and achieved his Diplom degree in Mechanical Engineering.