Roland Schmehl

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Verified

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• Dr.
• Professor (Associate) at Delft University of Technology

A detailed computational analysis of the oxidizer preflow during startup of a storable propellant upper-stage rocket engine is presented. This low-pressure flow regime is controlled by various two-phase phenomena, particularly flash atomization and flash evaporation of superheated liquid oxidizer, leading to a significant temperature drop in the co...

This book provides in-depth coverage of the latest research and development activities concerning innovative wind energy technologies intended to replace fossil fuels on an economical basis. A characteristic feature of the various conversion concepts discussed is the use of tethered flying devices to substantially reduce the material consumption pe...

The traction force of a kite can be used to drive a cyclic motion for extracting wind energy from the atmosphere. This paper presents a novel quasi-steady modelling framework for predicting the power generated over a full pumping cycle. The cycle is divided into traction, retraction and transition phases, each described by an individual set of anal...

This reference offers an overview of the field of airborne wind energy. As the first book of its kind, it provides a consistent compilation of the fundamental theories, a compendium of current research and development activities as well as economic and regulatory aspects. In five parts, the book demonstrates the relevance of Airborne Wind Energy an...

Leading-edge inflatable (LEI) kites are morphing aerodynamic surfaces that are actuated by the bridle line system. Their design as tensile membrane structures has several implications for the aerodynamic performance. Because of the pronounced C-shape of the wings, a considerable part of the aerodynamic forces is redirected sideways and used for ste...

Airborne wind energy (AWE) is an innovative technology that differs from the operating principles of horizontal axis wind turbines (HAWTs). It uses tethered flying devices, denoted as kites, to harvest higher-altitude wind resources. Kites eliminate the need for a tower but introduce a penalty in power generation since the kite has to spend part of...

This study investigates the relationship between sound quality metrics (SQMs) and noise annoyance caused by airborne wind energy systems (AWESs). In a controlled listening experiment, 75 participants rated their annoyance on the International Commission on Biological Effects of Noise (ICBEN) scale in response to recordings from in-field measurement...

This study demonstrates how kites used to generate wind energy can act as sensors to measure wind conditions and system behaviour. By combining data from existing sensors, such as those measuring position, speed, and forces on the tether, a sensor fusion technique accurately estimates wind conditions and kite performance. This approach can be integ...

The computational study compares the performance of circular and figure-of-eight flight patterns for fixed-wing ground-generation airborne wind energy (AWE) systems using a PID-based basic controller that effectively controls the kite during each patterns pumping cycle in a Matlab® Simulink® environment. A simple, adjustable control framework enabl...

Flexible membrane wings for kite sports, paragliding and airborne wind energy are highly manoeuvrable aerodynamic devices. The manoeuvrability can be quantified by the achievable turning rate of the wing and the dead time between the steering input and the actual flight dynamic response. In this paper, we present an onboard sensor system for measur...

So far, the size of horizontal axis wind turbines (HAWTs) has steadily increased, but recent studies and market decisions suggest that this trend may come to an end. Airborne wind energy (AWE) is an innovative technology that differs from the operating principles of HAWTs. It uses tethered flying devices, denoted as kites, to harvest higher-altitud...

The economic viability of future large-scale airborne wind energy systems critically hinges on the achievable power output in a given wind environment and the system costs. This work presents a fast model for estimating the net power output of fixed-wing ground-generation airborne wind energy systems in the conceptual design phase. In this quasi-st...

The present study investigates the relationship between sound quality metrics (SQMs) and noise annoyance for 10 airborne wind energy systems (AWESs) reported in a listening experiment. A convenience sample of 75 participants rated their annoyance on the International Commission on Biological Effects of Noise (ICBEN) scale in response to nine record...

Flexible membrane wings for kite sports, paragliding and airborne wind energy are highly manoeuvrable aerodynamic devices. The manoeuvrability can be quantified by the achievable turning rate of the wing and the dead time between the steering input and the actual flight-dynamic response. In this paper, we present an onboard sensor system for measur...

The economic viability of large-scale future airborne wind energy systems critically hinges on the achievable power output in a given wind environment and the system costs. This work presents a fast model for estimating the net power output of fixed-wing ground-generation airborne wind energy systems in the conceptual design phase. In this quasi-st...

Three unsteady aerodynamic tools at different levels of fidelity and computational cost were used to investigate the unsteady aerodynamic behavior of a delta kite applied to airborne wind energy. The first tool is an in‐house unsteady panel method that is fast but delivers low to mid fidelity predictions. The second tool uses the open‐source CFD co...

The flexible-membrane kite employed by some airborne wind energy systems uses a suspended control unit, which experiences a characteristic swinging motion relative to the top of the kite during sharp turning manoeuvres. This paper assesses the accuracy of a two-point kite model in resolving this swinging motion using two different approaches: appro...

This paper presents a quasi-steady simulation framework for soft-wing kites with suspended control unit employed for airborne wind energy. The kites are subject to actuation-induced and aero-elastic deformation and are described by a coupled aero-structural model in a virtual wind tunnel setup. Key contributions of the present work are a kinetic dy...

Airborne wind energy is an emerging technology that uses tethered flying devices to capture stronger and more steady winds at higher altitudes. Compared to smaller systems, megawatt-scale systems are substantially affected by gravity during flight operation, resulting in power fluctuations. MegAWES, a 3 MW reference model, experiences power fluctua...

Novel wind technologies, in particular airborne wind energy (AWE) and floating offshore wind turbines, have the potential to unlock untapped wind resources and contribute to power system stability in unique ways. So far, the techno-economic potential of both technologies has only been investigated at a small scale, whereas the most significant bene...

Abstracts and additional illustrations.

Although technologically challenging, airborne wind energy systems have several advantages over conventional wind turbines that make them an interesting option for deployment on Mars. However, the environmental conditions on the red planet are quite different from those on Earth. The atmosphere’s density is about 100 times lower, and gravity is abo...

Renewable energy for Mars habitats is of key interest for future crewed missions. However, the low solar irradiation and low atmospheric pressure on Mars pose serious challenges to exploiting these resources reliably. In this chapter, we investigate the technical feasibility of a soft-kite-based airborne wind energy system and its potential to powe...

In order for off-Earth top surface structures built from regolith to protect astronauts from radiation, they need to be several metres thick. In a feasibility study, funded by the European Space Agency, Technical University Delft (TUD aka TU Delft) explored the possibility of building in empty lava tubes to create rhizomatic subsurface habitats. Wi...

Airborne wind energy (AWE) is an emerging renewable energy technology that uses kites to harvest winds at higher altitudes than wind turbines. Understanding how residents experience a local AWE system (AWES) is important as the technology approaches commercialization. Such knowledge can help adjust the design and deployment of an AWES to fit locals...

Through its scalability, the AirborneWind Energy (AWE) technology opens up new markets and locations for wind energy, which allows AWE to play a significant part in the future energy system. The objective of Task 48 on AWE is to tackle a variety of specific challenges on a global scale, in addition to addressing and including stakeholders who are n...

The flexible membrane kite employed by some airborne wind energy systems carries a suspended control unit capable of inducing a characteristic pitch and roll swinging motion during sharp turning manoeuvres. This paper assesses how accurately a two-point kite model approximates this swinging motion with two approaches: approximated as a transition t...

Layout optimisation is essential for improving the overall performance of offshore wind farms. During the past 15 years, the use of yield optimisation algorithms has resulted in a transition from regular to more irregular farm layouts. However, since the layout affects many factors, yield optimisation alone may not maximise the overall performance....

Airborne wind energy systems using flexible membrane wings have the advantages of a low weight, small packing volume, high mobility and rapid deployability. This paper investigates the aero-structural deformation of a leading edge inflatable kite for airborne wind energy harvesting. In the first step, a triangular two-plate representation of the wi...

The majority of remote locations not connected to the main electricity grid rely on diesel generators to provide electrical power. High fuel transportation costs and significant carbon emissions have motivated the development and installation of hybrid power systems using renewable energy such these locations. Because wind and solar energy is inter...

Airborne wind energy systems benefit from high-lift airfoils to increase power output. This paper proposes an optimisation approach for a multi-element airfoil of a fixed-wing system operated in pumping cycles to drive a drum-generator module on the ground. The approach accounts for the different design objectives of the tethered kite’s alternating...

Integrating the operation of airborne wind energy systems safely into the airspace requires a systematic qualification process. It seems likely that the European Union Aviation Safety Agency will approve commercial systems as unmanned aircraft systems within the “specific” category, requiring risk-based operational authorization. In this paper, we...

Soft-wing kites for airborne wind-energy harvesting function as flying tensile membrane structures, each of whose shape depends on the aerodynamic load distribution and vice versa. The strong two-way coupling between shape and loading poses a complex fluid-structure interaction problem. Since computational models for such problems do not yet meet t...

High aerodynamic efficiency is a key design driver for airborne wind energy systems as it strongly affects the achievable energy output. Conventional fixed-wing systems generally use aerofoils with a high thickness-to-chord ratio to achieve high efficiency and wing loading. The box wing concept suits thinner aerofoils as the load distribution can b...

Inflatable wings are of interest for applications where low weight, compact transport volume, and easy set-up are important. Examples are unmanned aerial vehicles with inflatable wings, paragliders and softkites for sport or airborne wind-energy applications. In this paper, a new method of designing and fabricating conformable inflatable wings by J...

Similar to parafoils, ram-air kites are flexible membrane wings inflated by the apparent wind and supported by a bridle line system. A major challenge in estimating the performance of these wings using a computer model is the strong coupling between the airflow around the wing and the deformation of the membrane structure. In this paper, we introdu...

In the current auction-based electricity market, the design of utility-scale renewable energy systems has traditionally been driven by the levelised cost of energy (LCoE). However, the market is gradually moving towards a subsidy-free era, which will expose the power plant owners to the fluctuating prices of electricity. This paper presents a compu...

A key motivation for airborne wind energy is its potential to reduce the amount of material required for the generation of renewable energy. On the other hand, the materials used for airborne systems’ components are generally linked to higher environmental impacts. This study presents comparative life-cycle analyses for future multi-megawatt airbor...

Layout optimisation is essential for improving the overall performance of offshore wind farms. During the past 15 years, the use of yield optimisation algorithms has resulted in a transition from regular to more irregular farm layouts. However, since the layout affects many factors, yield optimisation alone may not maximise the overall performance....

Currently developed airborne wind energy systems have reached sizes of up to several hundred kilowatts. This paper presents the high-level design and a six-degrees-of-freedom model of a future fixed-wing airborne wind energy system operated in pumping cycles. This framework is intended to be used as an open-source reference system. The fixed-wing a...

In order for off-Earth top surface structures built from regolith to protect astronauts from radiation, they need to be several metres thick. With support from European Space Agency (ESA) and Vertico, the Technical University Delft (TUD) advanced research into constructing habitats in empty lava tubes on Mars in order to create subsurface habitats....

In pumping airborne wind energy (AWE) systems, the kite is operated in repetitive crosswind patterns, pulling the tether from a winch that drives a generator on the ground. During the reel-out phase of its operation, it produces power, whereas, during the reel-in phase, it consumes a small fraction of the produced power. This leads to an oscillatin...

Leading-edge inflatable (LEI) kites use a pressurized tubular frame to structurally support a single skin membrane canopy. The presence of the tubes on the pressure side of the wing leads to characteristic flow phenomena for this type of kite. In this paper, we present steady-state Reynolds-Averaged Navier-Stokes (RANS) simulations for a LEI wing f...

Airborne wind energy (AWE) systems use tethered flying devices to harvest higher-altitude winds to produce electricity. For the success of the technology, it is crucial to understand how people perceive and respond to it. If concerns about the technology are not taken seriously, it could delay or prevent implementation, resulting in increased costs...

The image shows a leading-edge inflatable (LEI) kite wing typically used for airborne wind energy applications. It is composed of a pressurized tubular frame to structurally support a single skin membrane canopy. Here, we present the results of Reynolds-Averaged Navier–Stokes (RANS) simulations for flow past the wing. The image shows a contour plot...

Currently developed airborne wind energy systems have reached sizes of up to several hundred kilowatts. This paper presents the high-level design and a six-degrees-of-freedom model of a future fixed-wing airborne wind energy system operated in pumping cycles. This framework is intended to be used as an open-source reference system. The fixed-wing air...

Steady-state Reynolds-Averaged Navier-Stokes (RANS) simulations are performed for a leading-edge inflatable wing for airborne wind energy applications. Expanding on previous work where only the inflatable leading edge tube was considered, eight additional inflatable strut tubes that support the wing canopy are now included. The shape of the wing is...

Airborne wind energy (AWE) systems use tethered flying devices to harvest higher-altitude winds to produce electricity. For a successful deployment of these systems, it is crucial to understand how the public perceives them. If public concerns about the technology are not taken seriously, implementation could be delayed or, in some cases, prevented...

Generating renewable energy on Mars is technologically challenging. Firstly, because, compared to Earth, key energy resources such as solar and wind are weak as a result of very low atmospheric pressure and low solar irradiation. Secondly, because of the harsh environmental conditions, the required high degree of automation, and the exceptional eff...

Computational simulation of the aerodynamics of a ram-air kite for airborne wind energy applications

Computational simulation of the aerodynamics of a ram-air kite for airborne wind energy applications

Flight dynamic and aerodynamic characterization of a softkite with suspended robotic control unit

TU Delft kite power flight data 2010 to 2015

Flight dynamic and aerodynamic characterization of a softkite with suspended robotic control unit

TU Delft kite power flight data 2010 to 2015

Airborne wind energy systems convert wind energy into electricity using tethered flying devices, typically flexible kites or aircraft. Replacing the tower and foundation of conventional wind turbines can substantially reduce the material use and, consequently, the cost of energy, while providing access to wind at higher altitudes. Because the fligh...

Generating renewable energy on Mars is technologically challenging. Firstly, because compared to Earth, key energy resources such as solar and wind are weak as a result of very low atmospheric pressure and low solar irradiation. Secondly, because of the harsh environmental conditions, the required high degree of automation and the exceptional effor...

Airborne wind energy (AWE) systems convert wind energy into electrical energy using autonomous tethered flying devices. Deemed a potentially game-changing solution to clean and sustainable energy generation, AWE is increasingly attracting the attention of governments, policymakers and industry worldwide. AWE technology can significantly reduce the...

The aerodynamic characteristics of a leading edge inatable (LEI) kite and a rigid-framed delta (RFD) kite were investigated. Flight data were recorded by using an experimental setup that includes an inertial measurement unit, a GPS, a magnetometer, and a multi-hole Pitot tube onboard the kites, load cells at every tether, and a wind station that me...

Airborne wind energy (AWE) systems are tethered flying devices that harvest wind resources at higher altitudes, which are not accessible to conventional wind turbines. To become a viable alternative to other renewable energy technologies, AWE systems are required to fly reliably and autonomously for long periods of time while being exposed to atmos...

Airborne wind energy (AWE) systems use tethered flying devices to harvest wind energy beyond the height range accessible to tower-based turbines. AWE systems can produce the electric energy with a lower cost by operating in high altitudes where the wind regime is more stable and stronger. For the commercialisation of AWE, system reliability and saf...

Airborne wind energy (AWE) is the conversion of wind energy into electricity using tethered flying devices. Replacing towered wind turbines by lightweight tensile structure not only reduces the material effort and thus cost of energy, but also provides access to an energy potential that has not been used so far, wind at higher altitudes. In this wo...

The design and computational model of a representative multi-megawatt airborne wind energy (AWE) system operated in pumping cycles is presented [1], together with a simulation framework that accounts for the flight dynamics of the fixed wing aircraft and the sagging of the tether, combining this with flight control and optimisation strategies to de...

In this paper we present a computational approach to simulate the steady-state aeroelastic deformation of a ram-air kite for airborne wind energy applications. The approach is based on a computational fluid dynamics (CFD) solver that is two-way coupled with a finite element (FE) solver. All components of the framework, including the meshing tools a...

Airborne wind energy (AWE) aims to harness wind energy at increasing altitudes by flying a device that is tethered to the ground. One of the existing concepts consists in using a leading edge inflatable (LEI) wing composed of a circular leading edge that is connected to a very thin canopy and supported by inflated struts

In this work we explore the initial design space for composite kites, focusing on the configuration of the bridle line system and its effect on the aeroelastic behaviour of the wing. The computational model utilises a 2D cross sectional model in conjunction with a 1D beam model (2+1D structural model) that captures the complex composite coupling ef...

In this paper, we present the design and computational model of a representative multi-megawatt airborne wind energy (AWE) system, together with a simulation framework that accounts for the flight dynamics of the fixed-wing aircraft and the sagging of the tether, combining this with flight control and optimisation strategies to derive the power cur...

Airborne wind energy (AWE) systems use tethered flying devices to harvest wind energy beyond the height range accessible to tower-based turbines. AWE systems can produce the electric energy with a lower cost by operating in high altitudes where the wind regime is more stable and stronger. For the commercialization of AWE, system reliability and saf...

In this paper we present a computational approach to simulate the steady-state aeroelastic deformation of a ram-air kite for airborne wind energy applications. The approach is based on a computational fluid dynamics (CFD) solver that is two-way coupled with a finite element (FE) solver. All components of the framework, including the meshing tools a...

The quasi-steady performance model (QSM) has been developed specifically for pumping airborne wind energy systems using flexible membrane wings. In this study, we validate this model using a comprehensive set of flight data that includes 87 consecutive pumping cycles and is acquired with the development platform of Kitepower B.V. The aerodynamic pr...

Airborne wind energy systems often use kites made of thin membranes to save material costs and increase mobility. However, this design choice increases the complexity of the aeroelastic behaviour of the system and demands high-fidelity tools. On the aerodynamic side of the multi-physics problem, it is quite challenging to create a high quality body...

In this work we present Reynolds-averaged Navier-Stokes (RANS) simulations of the flow past the constant design shape of a leading-edge inflatable (LEI) wing. The simulations are performed with a steady-state solver using a k − ω SST turbulence model, covering a range of Reynolds numbers between 10 5 ≤ and ≤ 15 × 10 6 and angles of attack varying b...

Airborne wind energy (AWE) systems harness energy at heights beyond the reach of tower-based wind turbines. To estimate the annual energy production (AEP), measured or modelled wind speed statistics close to the ground are commonly extrapolated to higher altitudes, introducing substantial uncertainties. This study proposes a clustering procedure fo...

Kites can be used to harvest wind energy with substantially lower material and environmental footprints and a higher capacity factor than conventional wind turbines. In this paper, we present measurement data from seven individual tow tests with the kite system developed by Kyushu University. This system was designed for 7 kW traction power and com...

Airborne wind energy (AWE) is the conversion of wind energy into electricity using tethered flying devices. Some concepts combine onboard wind turbines with a conducting tether, while others convert the pulling power of the flying devices on the ground. Replacing the tower of conventional wind turbines by a lightweight tether substantially reduces...

Kites can be used to harvest wind energy at higher altitudes while using only a fraction of the material required for conventional wind turbines. In this work, we present the kite system of Kyushu University and demonstrate how experimental data can be used to train machine learning regression models. The system is designed for 7 kW traction power...

Airborne wind energy (AWE) systems are tethered flying devices that harvest wind resources at higher altitudes which are not accessible to conventional wind turbines. In order to become a viable alternative to other renewable energy technologies, AWE systems are required to fly reliably and autonomously for long periods of time while being exposed...

A novel immersed boundary method based on a domain decomposition approach is proposed in the context of a finite element discretisation method. It is applicable to incompressible flows past rigid, deforming, or moving bodies. In this method, unlike most immersed boundary methods, strong boundary conditions are imposed in the regions of the computat...

Roland Schmehl presenting at the Emerging Technologies Seminar "Airborne & Floating Wind" on Wednesday 5th February 2020 in Ostend, Belgium, at the GreenBridge business incubator and science park of Ghent University. Video recording available from https://youtu.be/QiYyCb5x2HA