Rüdiger Höffer’s research while affiliated with Ruhr-Universität Bochum and other places

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Publications (98)


Vortex shedding load on a full-scale wind turbine tower at transcritical Reynolds numbers
  • Article

July 2024

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53 Reads

Journal of Wind Engineering and Industrial Aerodynamics

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Rüdiger Höffer

As the size of modern wind turbines increases, the phenomenon of vortex resonance, which occurs at lower critical speeds due to lower natural frequencies of larger turbines, becomes more significant. Vortex shedding in the wake of a slender structure is still not fully investigated, particularly with regard to the Reynolds number mismatch between small-scale models and the full-scale structure. The vortex shedding load with Re = 4-10x10^6 is addressed in this paper by investigating a full-scale measurement on a large wind turbine tower. The aerodynamic coefficients and vortex shedding load parameters are studied based on the measurement of wind pressure around the circumference of the tower. The results are compared to previous studies and values suggested in related standards. A detailed methodology for data evaluation is presented. As local parameters have been measured, the work marks the distinction between local and global parameters, in particular for the Strouhal number. Although this paper focuses on the tower-only configuration (without nacelle), the measurements are also carried out for a turbine including rotor-nacelle assembly (RNA), which allows the effect of blade position and rotation of the parked wind turbine on the lift coefficient of the tower to be studied.


Field measurement data set of wind turbine tower for enhanced calculation of vortex-induced vibration
  • Article
  • Full-text available

June 2024

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37 Reads

Journal of Physics Conference Series

From July 2021, a full-scale measurement campaign is carried out on two wind turbine towers with smooth surfaces (k/D ≈ 1.0·10- ⁶ ). Tower response (through accelerations) and wind pressure on the surface are measured. Throughout the one-year monitoring period, there were challenges in transferring full-scale data into a ready-to-use VIV data set. For example, the spatially varying wind conditions despite the small distance between the met masts and the towers. This work aims to provide a ready-to-use full-scale data set for the development of VIV prediction models. A data selection approach based on three simultaneous measurements of wind conditions and maximum moving standard deviation of oscillations s proposed. In addition, the load parameters obtained from the wind pressure measurements in the field and from wind tunnel tests are considered. An enhanced calculation is carried out by defining local aerodynamic damping for sectional heights of the tower. A comparison of the data set with the calculated response is presented to assess the calculation method and to give ideas on sensitive input parameters considering the full-scale condition.

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An enhanced analytical calculation model based on sectional calculation using a 3D contour map of aerodynamic damping for vortex induced vibrations of wind turbine towers

June 2024

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443 Reads

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1 Citation

Wind and Structures

To model the aeroelasticity in vortex-induced vibrations (VIV) of slender tubular towers, this paper presents an approach where the aerodynamic damping distribution along the height of the structure is calculated not only as a function of the normalized lateral oscillation but also considering the local incoming wind velocity ratio to the critical velocity (velocity ratio). The three-dimensionality of aerodynamic damping depending on the tower's displacement and the velocity ratio has been observed in recent studies. A contour map model of aerodynamic damping is generated based on the forced vibration tests. A sectional calculation procedure based on the spectral method is developed by defining the aerodynamic damping locally at each increment of height. The proposed contour map model of aerodynamic damping and the sectional calculation procedure are validated with full-scale measurement data sets of a rotorless wind turbine tower, where good agreement between the prediction and measured values is obtained. The prediction of crosswind response of the wind turbine tower is performed over a range of wind speeds which allows the estimation of resulting fatigue damage. The proposed model gives more realistic prediction in comparison to the approach included in current standards.


Mitigation of Interference-Induced Vibrations for Towers in Group Arrangements

February 2024

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30 Reads

The paper studies tower vibrations in closely spaced group arrangements due to vortex excitation and interference galloping. The ever-growing development of the wind energy industry has recently led to an in-depth examination of the subject, particularly with regard to the transport of towers for offshore wind turbines. Due to the low natural frequencies typical of steel towers and the need of assembling, transporting and installing towers in all possible weather scenarios, the range of verification for aeroelastic instabilities is extended until very high reduced wind velocities. The paper presents a synthesis of aeroelastic wind tunnel tests of towers in several group arrangements for spacings a/D = 1.25, 1.50, 1.875, 2.5 (being “a” the axis-to-axis distance). The Scruton number is varied in the experiments between 13 and 77. The paper shows that Scruton number effects on vortex-induced vibrations, on interference galloping and on their mechanisms of interaction are considerable. Increasing the Scruton number not only shifts the onset velocity of galloping towards higher values (in accordance with Eurocode), but also changes the behaviour of the galloping branch and reduces the range of galloping-prone wind directions. In all cases where vortex-induced oscillations act as a trigger for interference galloping, increasing the Scruton number can be used to effectively eliminate the occurrence of galloping instabilities.


Insights into the Transcritical Reynolds Number Range Based on Field Measurements of a Wind Turbine Tower

February 2024

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85 Reads

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1 Citation

The estimation of vortex shedding load is essential for the prediction of Vortex-Induced Vibration (VIV) on slender bodies. The application of the VIV model to a full-scale slender tower, such as wind turbine towers and chimneys, depends on the estimation of actual vortex shedding load under field conditions. This paper aims to provide insight on the vortex shedding spectrum with a real-life wind and the transcritical flow-regime, which requires high effort to observe in the wind tunnel scale. The vortex shedding spectrum is evaluated from the response measurement is focused on this paper, where challenges from the investigation and an introduction to the wind pressure measurement are then discussed. Global Strouhal number at high Reynolds numbers, spectrum of tower response in lift direction, and the estimation of critical velocity are presented. The influence of ambient condition such as wind profile, wind direction and turbulence intensity are included.


Validation of URANS Simulations of a Small-Scale Vertical Axis Wind Turbine using OpenFOAM

August 2023

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10 Reads

In this study, simulation results of a CFD investigation of a Vertical Axes Wind Turbine (VAWT) using the opensource code OpenFOAM (OF) are shown. 2D URANS simulations of a 3-bladed VAWT operating under various tip speed ratios were performed with the K-Omega-SST turbulence model. The main goals are to investigate the potential and limitations of OF for this application. Conclusions show that simulations using a moving mesh with an Arbitrary Mesh Interface (AMI) can be challenging, and it highly affects the meshing techniques and the solution’s resolution. Despite the medium-sized mesh, the model is able to predict the experimental power coefficients and is validated against wind tunnel data.


Field measurement data set of wind turbine tower for enhanced calculation of vortex-induced vibration

August 2023

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345 Reads

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1 Citation

From July 2021, a full-scale measurement campaign is carried out on two wind turbine towers with smooth surfaces (k/D ~ 1.0∙10-6). Tower response (through accelerations) and wind pressure on the surface are measured. Throughout the one-year monitoring period, there were challenges in transferring full-scale data into a ready-to-use VIV data set. For example, the spatially varying wind conditions despite the small distance between the met masts and the towers. This work aims to provide a ready-to-use full-scale data set for the development of VIV prediction models. A data selection approach based on three simultaneous measurements of wind conditions and maximum moving standard deviation of oscillation is proposed. In addition, the load parameters obtained from the wind pressure measurements in the field and from wind tunnel tests are considered. An enhanced calculation is carried out by defining local aerodynamic damping for sectional heights of the tower. A comparison of the data set with the calculated response is presented to assess the calculation method and to give ideas on sensitive input parameters considering the full-scale condition.


Figure 3.1 Pressure distribution at z/H = 0.82 from measurement on SG 14-222 DD (File: Fig6_PressureDistribution)
Full-scale tests on wind turbine towers: towards a realistic prediction of vortex-induced vibrations

August 2023

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749 Reads

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6 Citations

This paper reports of the ongoing measurement campaign on two prototype wind turbine towers of the Siemens Gamesa Renewable Energy in Østerild, Denmark. The latest evaluation and measurement results in this paper are also presented during the 97th CICIND conference in Paphos, Cyprus, which includes the evaluation of the measured pressure distribution and aerodynamic coefficients in the transcritical flow of the free-standing wind turbine tower. This allows further clarification on the full-scale transcritical regime and direct estimation of the vortex shedding load. Considering the objectives of the campaign to transfer existing knowledge of vortex-induced vibrations (VIV) derived from wind tunnel tests under controlled experimental conditions to full-scale structures in real environment, the response of the tower due to vortex resonance is assessed and issues regarding the variability of wind conditions are discussed.


Insights into the transcritical Reynolds number range based on field measurements of a wind turbine tower

August 2023

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227 Reads

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2 Citations

The estimation of vortex shedding load is essential for the prediction of Vortex-Induced Vibration (VIV) on slender bodies. The application of the VIV model to a full-scale slender tower, such as wind turbine towers and chimneys, depends on the estimation of actual vortex shedding load under field conditions. This paper aims to provide insight on the vortex shedding spectrum with a real-life wind and the transcritical flow-regime, which requires high effort to observe in the wind tunnel scale. The vortex shedding spectrum is evaluated from the response measurement is focused on this paper, where challenges from the investigation and an introduction to the wind pressure measurement are then discussed. Global Strouhal number at high Reynolds numbers, spectrum of tower response in lift direction, and the estimation of critical velocity are presented. The influence of ambient condition such as wind profile, wind direction and turbulence intensity are included.


Aerodynamic damping functions in vortex-induced vibrations for structures with sharp edges

June 2023

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46 Reads

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2 Citations

Journal of Wind Engineering and Industrial Aerodynamics

Ultimate limit state and fatigue analyses of slender structures in vortex-induced vibrations require knowledge of aerodynamic damping in the lock-in range. The aerodynamic damping depends primarily on the shape of the cross section. The paper provides an experimental database of aerodynamic damping functions for different shapes, with a focus on sharp-edged cross sections. The data are discussed with respect to existing results available for circular cross sections. The aerodynamic damping is measured directly through wind tunnel tests in forced vibrations. Wind tunnel tests in free vibrations are used to extend the functions in the range of large oscillations and to validate the model. This concept is implemented in a well-founded calculation method for vortex induced vibrations for the design of slender structures. This is suitable for code applications and is in line with the procedure described in the latest generation of Eurocode. The novelty with respect to previous models like the Vickery&Basu model consists in an aerodynamic damping parameter with positive curvature. This can be easily controlled for varying cross sections by changing the value of the function exponent


Citations (42)


... The realistic wind profile is proposed to be applied in the evaluation of vortex excitation on slender structure, which shows the importance of locally defined parameters along the height. The importance of locally definition and evaluation of parameters in predicting VIV for wind turbine tower is also introduced and explored in (Livanos, 2018;Livanos et al., 2024). ...

Reference:

Vortex shedding load on a full-scale wind turbine tower at transcritical Reynolds numbers
An enhanced analytical calculation model based on sectional calculation using a 3D contour map of aerodynamic damping for vortex induced vibrations of wind turbine towers
  • Citing Article
  • June 2024

Wind and Structures

... For model development, it is essential to collect a strategic data set such that the parameters in the calculation can be clearly addressed. More details of data set compilation are included in (Kurniawati et al. 2023). In this paper, a data set type compiled based on consecutive 10minute data intervals for several hours during a VIV event will be used for validation of the proposed sectional calculation and contour map model. ...

Field measurement data set of wind turbine tower for enhanced calculation of vortex-induced vibration

... The wind pressure measurement uses 24 differential pressure sensors along the tower circumference on two levels z/H = 0.63 and z/H = 0.82. Details of measurements are given in [12]. To obtain the displacement at the top of the tower, the bending moment signal recorded at the bottom using four bridge strain gauges or the acceleration around the top of the tower are used. ...

Full-scale tests on wind turbine towers: towards a realistic prediction of vortex-induced vibrations

... Currently, wind tunnel tests are commonly used to determine the equivalent aerodynamic damping, taking into account the AN of crosswind vibration in tall buildings. The forced vibration test is utilized to separate the self-excited wind loads from the total wind loads and identify the equivalent aerodynamic damping [28,29]. Steckley determined the equivalent aerodynamic damping of a tall building with a square section through forced vibration tests, as shown in Figure 4 [30]. ...

Aerodynamic damping functions in vortex-induced vibrations for structures with sharp edges
  • Citing Article
  • June 2023

Journal of Wind Engineering and Industrial Aerodynamics

... This refers to the damage equivalent moment for a selected duration, for which the total number of cycles is calculated as N ref =f n •T, where T is the time in seconds. (Lupi et al. 2020) determine the fatigue damage based on rainflow counting of time series measured in wind tunnel tests, where the determined "equivalent peak factor for fatigue analysis" is around 1.42. According to Eq. (24), the corresponding factor is 3.363/2=1.68. ...

FATIGUE LIFE ESTIMATION CONSIDERING THE QUASI-PERIODIC CROSS-WIND RESPONSE OF SLENDER STRUCTURES IN THE LOCK-IN RANGE
  • Citing Conference Paper
  • January 2020

... In addition, this quantity seems to be lower also when compared with other two selected studies, herein deepened. The first study, which focuses on a cantilevered structure characterized by a constant circular cross section, has been recently published by Lupi et al. (2021). The second one is an investigation documented by Scruton (1963) on a full aeroelastic model of a tapered stack with a lower taper ratio than the one adopted in the present study. ...

Aerodynamic damping in vortex resonance from aeroelastic wind tunnel tests on a stack

Journal of Wind Engineering and Industrial Aerodynamics

... This facilitates the ability to deal with aeroelasticity locally, for example through aerodynamic damping defined locally at each level of tower's height. The 3D aerodynamic damping contour map model from (Livanos et al., 2024) based on the experimental results of (Lupi et al., 2018), can be used to calculate the effect of variation of two parameters along the height on the aeroelasticity when tower experiences lock-in. ...

Aerodynamic damping model in vortex-induced vibrations for wind engineering applications
  • Citing Article
  • March 2018

Journal of Wind Engineering and Industrial Aerodynamics

... Indeed, while wind power generation and solar energy collection in buildings have been extensively studied and practically applied, the integration of raindrop energy collection in smart buildings still lacks sufficient research and faces several challenges [27][28][29][30]. These challenges include selecting the energy conversion method, designing and optimizing the energy collectors, and determining how the collectors and the building can collaborate to maximize energy conversion efficiency [31]. Therefore, researching the integration and utilization of raindrop energy in buildings can make a significant contribution to the development of green buildings. ...

On the Flow over High-rise Building for Wind Energy Harvesting: An Experimental Investigation of Wind Speed and Surface Pressure

Applied Sciences

... Value (m) the accelerometers will be used to extract the modal parameters by using operational modal analysis technique, which makes use of only the output data. The strain time history data recorded by the strain gauges will be used to compute the principal stresses, bending moments and for performing fatigue analysis using the rain flow counting method [28]. This Solar Chimney Project in Aswan, although it is a small scale research project, can serve as an ideal experimental field for future commercial implementation of the already designed large solar updraft towers, some of them reaching up to a height of about 1000m and higher [29]. ...

Monitoring Based Identification for Structural Life Cycle Management of Wind Energy Converters
  • Citing Chapter
  • March 2016

... Data-in-Motion (DIM) Module: The Data-in-Motion module comprises layer 1 to layer 3. Layer 1 (Physical Devices and Controllers): Vibration, environmental, and operational IIoT devices are mounted to monitor critical components in an offshore wind farm [35]. Considering their application environment, these IIoT devices are ruggedized to withstand harsh environmental conditions such as extreme temperatures, humidity, vibrations, and exposure to dust and chemicals. ...

Lessons learned from practical structural health monitoring of offshore wind turbine support structures in the North Sea