Nikolaos Stergiannis

Nikolaos Stergiannis

Brussels Metropolitan Area
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About

I am Nikolaos Stergiannis, a mechanical engineer, researcher, and project advisor with…

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Experience

  • European Innovation Council and SMEs Executive Agency (EISMEA) Graphic

    European Innovation Council and SMEs Executive Agency (EISMEA)

    Bd Simon Bolivar 34, 1000 Bruxelles

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    Brussels Area, Belgium

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    Brussels Area, Belgium

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    Brussels, Brussels Region, Belgium

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    Pl. Charles Rogier 16, 1210 Saint-Josse-ten-Noode

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    Brussels, Brussels Region, Belgium

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    Brussels, Brussels Region, Belgium

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    Brussels Area, Belgium

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    Brussels

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    Brussels, Brussels Region, Belgium

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    Brussels, Brussels Region, Belgium

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    Brussels Area, Belgium

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    Brussels

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    Brussels Area, Belgium

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    Thessaloniki Industrial Complex P.O. Box 100 44, GR-541 10 Thessaloniki, Greece

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    Thessaloniki Industrial Complex P.O. Box 100 44, GR-541 10 Thessaloniki, Greece

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    Thessaloniki

Education

  • Vrije Universiteit Brussel Graphic

    Vrije Universiteit Brussel

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    Non-Deterministic Advanced CFD Modelling of Wind Turbine Wakes and their Interaction with Applications to Wind Farms including Complex Terrain Effects

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    Collaborative Ph.D. Researcher

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    Activities and Societies: Energy Conversion Systems, Energy Transport, Renewable Energy Sources, Energy Planning of Buildings, Environment and Energy, Industrial Systems and Energy Policy, Management of Industrial Energy Units.

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Licenses & Certifications

  • Certificate of Proficiency in English (Council of Europe Level C2)

    University of Central Lancashire

    Issued
    Credential ID 107-ATH-E877010
  • European Computer Driving Licence Graphic

    European Computer Driving Licence

    ECDL Foundation

    Issued
    Credential ID GR20294

Volunteer Experience

  • EUvsVirus Graphic

    Head of Account Managers

    EUvsVirus

    - Present 4 years 8 months

    Disaster and Humanitarian Relief

Publications

  • The Effect of Wind Energy on Microclimate: Lessons Learnt from a CFD Modelling Approach in the Case Study of Chios Island

    Applied Sciences

    During the last three decades, rapid growth of wind energy has led to questions regarding the possible impacts of wind farms on local weather and microclimates. Physically, the increased turbulence due to the wind turbine operation affects the mixing processes, may slightly disturb the pressure and temperature distributions downstream of wind farms and may have an impact on natural ecosystems such as the famous mastic tree population located on the island of Chios in the North Aegean Sea. This…

    During the last three decades, rapid growth of wind energy has led to questions regarding the possible impacts of wind farms on local weather and microclimates. Physically, the increased turbulence due to the wind turbine operation affects the mixing processes, may slightly disturb the pressure and temperature distributions downstream of wind farms and may have an impact on natural ecosystems such as the famous mastic tree population located on the island of Chios in the North Aegean Sea. This study explores the wind farms and their wake effects downstream with a particular focus on the effect on the southern part of the island where the mastic trees cultivation is located. The analysis is carried out with the use of the commercial CFD code ANSYS Fluent. Steady state computations of full 3D Navier–Stokes equations, using the k-ε turbulence closure scheme are carried out. The development of the multiple wake effects of the wind farms and their propagation downstream is examined under low and high turbulence intensities. Results clearly indicate that for both test cases there is no impact to the local microclimate and to the mastic Tree population.

    Other authors
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  • Full HAWT rotor CFD simulations using different RANS turbulence models compared with actuator disk and experimental measurements

    Wind Energy Science

    The development of large-scale wind energy projects has created the demand for increasingly accurate and efficient models that limit a project's uncertainties and risk. Wake effects are of great importance and are relevant for the optimization of wind farms. Despite a growing body of research, there are still many open questions and challenges to overcome. In computational modelling, there are always numerous input parameters such as material properties, geometry, boundary conditions, initial…

    The development of large-scale wind energy projects has created the demand for increasingly accurate and efficient models that limit a project's uncertainties and risk. Wake effects are of great importance and are relevant for the optimization of wind farms. Despite a growing body of research, there are still many open questions and challenges to overcome. In computational modelling, there are always numerous input parameters such as material properties, geometry, boundary conditions, initial conditions, turbulence modelling etc. whose estimation is difficult and their values are often inaccurate or uncertain. Due to the lack of information of several sources, e.g., uncertainties present in operating conditions as well as in the mathematical modelling, the computational output is also uncertain. It is therefore very important to validate the mathematical models with experiments performed in controlled conditions. In the present paper, the single wake characteristics of a Horizontal-Axis Wind Turbine Rotor (HAWT) and their spatial evolution are investigated with different Computational Fluid Dynamics (CFD) modelling approaches and compared to experimental measurements. The steady state 3-D Reynolds-Averaged Navier Stokes (RANS) equations are solved in the open-source platform OpenFOAM, using different turbulence closure schemes. For the full-rotor CFD simulations, the Multiple Reference Frames (MRF) approach was used to model the rotation of the blades. For the simplified cases, an actuator disk model was used with the experimentally measured thrust (CT) and power (CP) coefficient values. The performance of each modelling approach is compared with experimental wind tunnel wake measurements from the 4th blind test organized by NOWITECH in 2015. Numerical results are compared with experimental data along three horizontal lines downstream, covering all the wake regions. Wake predictions are shown to be very sensitive to the choice of the RANS turbulence model.

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  • CFD modelling approaches against single wind turbine wake measurements using RANS

    IOP Publishing

    Numerical simulations of two wind turbine generators including the exact geometry of their blades and hub are compared against a simplified actuator disk model (ADM). The wake expansion of the upstream rotor is investigated and compared with measurements. Computational Fluid Dynamics (CFD) simulations have been performed using the open-source platform OpenFOAM [1]. The multiple reference frame (MRF) approach was used to model the inner rotating reference frames in a stationary computational…

    Numerical simulations of two wind turbine generators including the exact geometry of their blades and hub are compared against a simplified actuator disk model (ADM). The wake expansion of the upstream rotor is investigated and compared with measurements. Computational Fluid Dynamics (CFD) simulations have been performed using the open-source platform OpenFOAM [1]. The multiple reference frame (MRF) approach was used to model the inner rotating reference frames in a stationary computational mesh and outer reference frame for the full wind turbine rotor simulations. The standard k — ε and k — ω turbulence closure schemes have been used to solve the steady state, three dimensional Reynolds Averaged Navier- Stokes (RANS) equations. Results of near and far wake regions are compared with wind tunnel measurements along three horizontal lines downstream. The ADM under-predicted the velocity deficit at the wake for both turbulence models. Full wind turbine rotor simulations showed good agreement against the experimental data at the near wake, amplifying the differences between the simplified models.

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  • Computational Investigation of Horizontal Axis Wind Turbine Single and Multiple Wakes

    EWEA - European Wind Energy Association

    The accurate calculation of wake development is crucial for the design of the layout and the operation of a wind farm. Simulating a wind farm with more than one fully detailed wind turbines and possibly complex terrain geometry requires significant computational power and time. For this reason the turbine rotors are approximated as discs which behave as momentum sinks and this is the approach that has been adopted in the present study which focuses on the development of a simplified rotor disc…

    The accurate calculation of wake development is crucial for the design of the layout and the operation of a wind farm. Simulating a wind farm with more than one fully detailed wind turbines and possibly complex terrain geometry requires significant computational power and time. For this reason the turbine rotors are approximated as discs which behave as momentum sinks and this is the approach that has been adopted in the present study which focuses on the development of a simplified rotor disc model. However, in the present contribution, in order to approximate the axial thrust across the disc in a more accurate manner, a radially varying thrust coefficient is utilized which is extracted from the CFD full rotor transient analysis results. The machine under investigation is the modified Grumman 20 kW turbine used by the National Renewable Energy Laboratory (NREL) for the Phase VI of the Unsteady Aerodynamics Experiment, tested in the wind tunnel at NASA Ames [Ref]. The analysis is carried out with the use of two commercial CFD codes, ANSYS CFX and ANSYS Fluent. Both steady and unsteady computations are carried out. For the full rotor simulation the time-averaged unsteady results are compared against the steady ones and with the results of the actuator disc approach. The effect of the use of different turbulence models is assessed. Two different turbulence models, k-ε and Shear Stress Transport were used along with the three dimensional RANS equations. The detailed assessment of the differences in the flow field as it is obtained from the steady and unsteady analysis of both full rotor and actuator disc approximations indicated that a good agreement exists between the two distributions and the existing differences are identified and quantified.

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  • CFD Modeling Approaches of Wind Turbine Single and Multiple Wakes

    EWEA - European Wind Energy Association

    Wake modeling of wind turbines has attracted a lot of attention by the research community during the past five years especially for very large offshore wind farm installations where wake effects are responsible for quite a significant percentage of power output losses. Although a number of analytical and semi-empirical simple models have been developed for wake modeling, they are not capable of providing satisfactory predictions for different turbulence conditions. However, the substantial…

    Wake modeling of wind turbines has attracted a lot of attention by the research community during the past five years especially for very large offshore wind farm installations where wake effects are responsible for quite a significant percentage of power output losses. Although a number of analytical and semi-empirical simple models have been developed for wake modeling, they are not capable of providing satisfactory predictions for different turbulence conditions. However, the substantial progress in computer resources has permitted cost efficient calculations using more sophisticated methods such as the solution of Navier-Stokes equations. In the present work, an in-house developed fully 3D Navier-Stokes solver using the k-ε turbulence closure scheme appropriately parameterized for atmospheric flows is compared against full scale measurements as well as against results from the commercial package FLUENT. It is concluded that the CFD models underestimate the wake effects for the near wake a behavior also observed by other investigators in the past. The multi wake problem is considered for the case of five wind turbines in a row where full scale power measurements are available. A number of techniques are tested to estimate the reference wind speed required to determine the thrust for the downstream rotors. It is shown that, under an increased computational cost, the most consistent technique to overcome this deficiency is to perform multi runs starting from the most upstream row and proceed gradually downstream.

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  • CFD modelling approaches of a wind turbine single wake effect in a wind farm with numerical solution

    University of Western Macedonia

    Diploma Thesis

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Honors & Awards

  • Research Project Scholarship

    INNOVIRIS

    INNOVIRIS is the institution in the Brussels-Capital Region encouraging scientific research and innovation. It supports and funds the Brussels-Capital Region’s R&D policy.

Languages

  • Greek

    Native or bilingual proficiency

  • English

    Full professional proficiency

  • French

    Professional working proficiency

  • Dutch

    Elementary proficiency

Organizations

  • AAAS

    Member

    - Present

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