articles by Jens Friedrichs
With the growth of aviation traffic and the demand for emission reduction, alternative fuels like... more With the growth of aviation traffic and the demand for emission reduction, alternative fuels like the so-called electrofuels could comprise a sustainable solution. Electrofuels are understood as those that use renewable energy for fuel synthesis and that are carbon-neutral with respect to greenhouse gas emission. In this study, five potential electrofuels are discussed with respect to the potential application as aviation fuels, being n-octane, methanol, methane, hydrogen and ammonia, and compared to conventional Jet A-1 fuel. Three important aspects are illuminated. Firstly, the synthesis process of the electrofuel is described with its technological paths, its energy efficiency and the maturity or research need of the production. Secondly, the physico-chemical properties are compared with respect to specific energy, energy density, as well as those properties relevant to the combustion of the fuels, i.e., autoignition delay time, adiabatic flame temperature, laminar flame speed and extinction strain rate. Results show that the physical and combustion properties significantly differ from jet fuel, except for n-octane. The results describe how the different electrofuels perform with respect to important aspects such as fuel and air mass flow rates. In addition, the results help determine mixture properties of the exhaust gas for each electrofuel. Thirdly, a turbine configuration is investigated at a constant operating point to further analyze the drop-in potential of electrofuels in aircraft engines. It is found that electrofuels can generally substitute conventional kerosene-based fuels, but have some downsides in the form of higher structural loads and potentially lower efficiencies. Finally, a preliminary comparative evaluation matrix is developed. It contains specifically those fields for the different proposed electrofuels where special challenges and problematic points are seen that need more research for potential application. Synthetically-produced n-octane is seen as a potential candidate for a future electrofuel where even a drop-in capability is given. For the other fuels, more issues need further research to allow the application as electrofuels in aviation. Specifically interesting could be the combination of hydrogen with ammonia in the far future; however, the research is just at the beginning stage.
Papers by Jens Friedrichs
International Journal of Turbomachinery, Propulsion and Power
Current civil aviation is characterized by rising cost and competitive pressure, which is partly ... more Current civil aviation is characterized by rising cost and competitive pressure, which is partly passed to the MRO (Maintenance, Repair and Overhaul) companies. To improve the maintenance, condition-based maintenance is established, which is characterized by tailored maintenance actions for each part of the jet engine, depending on the individual engine history and operating conditions. Thereby, prediction models help engineers to authorize maintenance actions as effectively as possible. This paper will help to improve these prediction models. Therefore, the influence of specific deterioration of a high pressure compressor (HPC) to jet engine performance parameters such as exhaust gas temperature (EGT) and specific fuel consumption (SFC) will be investigated. For this purpose, computational fluid dynamic (CFD) calculations of deteriorated HPC geometries are carried out and serve as a basis to scale the reference HPC performance characteristics to deteriorated ones. To evaluate the changes in performance parameters, a modular performance synthesis model is set up. In this model, the HPC map is exchanged with deteriorated ones. As a result, the influence of geometric deviations to the design intent can be determined, and the MRO companies are able to focus on the most relevant sections of the compressor blading.
Machines, 2022
A mobile fuel cell systems power output can be increased by pressure amplification using an elect... more A mobile fuel cell systems power output can be increased by pressure amplification using an electric turbocharger. These devices are subject to frequent transient manoeuvres due to a multitude of load changes during the mission in automotive applications. In this paper, the authors describe a simulation approach for an electric turbocharger, considering the impact of moist air and condensation within the cathode gas supply system. Therefore, two simulation approaches are used: an iterative simulation method and one based on a set of ordinary differential equations. Additional information is included from turbine performance maps taking into account condensation using Euler–Lagrange CFD simulations, which are presented. The iterative calculation approach is well suited to show the impact of condensation and moist air on the steady state thermodynamic cycle and yields a significant shift of the steady state operating line towards the surge line. It is shown that a substantial risk of ...
Applied Mechanics, 2022
The design of flexible and efficient aircraft engines and propulsion systems plays a crucial role... more The design of flexible and efficient aircraft engines and propulsion systems plays a crucial role in the development of future low-emission aircraft. Implementing shape-variable blades to compressor front stage rotors presents a high potential for increasing efficiency, since through adaptation, the blades are capable of optimizing their shape for different flight phases and aerodynamic conditions. Modifying the shape of the blades by using structurally integrated actuators allows this adaptation and therefore helps enhance their aerodynamic behavior for different flight regimes. Since up to now no morphing compressor or any other aircraft engine blades exist, here a multidisciplinary method for their design is introduced. This new method brings together existing structural and aerodynamic design methodologies, couples them together already at the earliest stages of the design process, while addressing the challenges that arise with a tightly coupled multidisciplinary design. As a r...
A transport aircraft concept featuring over-the-wing-mounted nacelles (OWN)positioned aft of the ... more A transport aircraft concept featuring over-the-wing-mounted nacelles (OWN)positioned aft of the wing's trailing edge is investigated with numerical methods. The objective of the study is to compare two different approaches for integrating the nacelle to the airframe from an aerodynamic point of view. On one hand, a pylon mounted OWN configuration is chosen for installing the propulsion system. On the other hand,a closer coupling between wing and nacelle by embedding the OWN into the wing is examined. Both configurations will be analysed at a representative reference position and discussed in terms of similarities and differences. Afterwards, a positioning study with a free flying nacelle is conducted to explore the aerodynamic sensitivities of wing and nacelle for this engine airframe integration position. The results show that a favourable position with the potential for drag reduction can be found.
International Journal of Gas Turbine, Propulsion and Power Systems, 2016
International Journal of Turbomachinery, Propulsion and Power, 2020
In modern aircraft engines, the low-pressure compressor (LPC) is subjected to a flow characterize... more In modern aircraft engines, the low-pressure compressor (LPC) is subjected to a flow characterized by strong wakes and secondary flows from the upstream fan. This concerns ultra-high bypass ratio (UHBR) turbofan engines, in particular. This paper presents the aerodynamic and aeroelastic sensitivities of parametric variations on the LPC, driven by the design considerations in the upstream fan. The goal of this investigation was to determine the influence of design-based geometry parameter variations on the LPC performance under realistic inlet flow distributions and the presence of an s-duct. Aerodynamic simulations are conducted at the design and off-design operating points with the fan outflow as the inlet boundary conditions. Based on the aerodynamic results, time-linearized unsteady simulations are conducted to evaluate the vibration amplitude at the resonance operating points. First, the bypass ratio is varied by reducing the channel height of the LPC. The LPC efficiency decreas...
For the supply of secondary air systems such as turbine cooling, oil sump and cabin ventilation, ... more For the supply of secondary air systems such as turbine cooling, oil sump and cabin ventilation, bleed air is taken from the compressor of aircraft engines. The design objective is to extract the required fluid with as little losses as possible. Bleed air is usually extracted at the casing downstream of the stator row. By shifting the extraction position by half a stage upstream, an improvement of the compressor efficiency could be achieved. In this measuring campaign the effect of a bleed air geometry is experimentially investigated downstream of the stator blade row as well as downstream of the rotor blade row of a 1.5-stage axial compressor. In the studies presented here, the differences of the configurations with respect to stage aerodynamics and aerodynamics of the bleed air geometry are shown. The aim is to investigate the potential of bleed air extraction downstream of the rotor blade row. Since the investigation of bleed air extraction in the rotating test rig has a higher c...
International Journal of Turbomachinery, Propulsion and Power, 2021
Radial turbines used in automotive fuel cell turbochargers operate with humid air. The gas expans... more Radial turbines used in automotive fuel cell turbochargers operate with humid air. The gas expansion in the turbine causes droplets to form, which then grow through condensation. The associated release of latent heat and decrease in the gaseous mass flow strongly influence the thermodynamics of the turbine. This study aims to investigate these phenomena. For this purpose, the classical nucleation theory and Young’s growth law are integrated into a Euler–Lagrange approach. The main advantages of this approach are the calculation of individual droplet trajectories and a full resolution of the droplet spectrum. The results indicate an onset of nucleation at the blade tip and in the tip gap, followed by nucleation over the entire blade span, depending on the humidity at the turbine inlet. With a saturated turbine inflow, condensation causes the outlet temperature to rise to almost the same level as at the inlet. In addition, condensation losses reduce the efficiency and the latent heat ...
Procedia CIRP, 2021
In today's business environment, the trend towards more product variety and customization is unbr... more In today's business environment, the trend towards more product variety and customization is unbroken. Due to this development, the need of agile and reconfigurable production systems emerged to cope with various products and product families. To design and optimize production systems as well as to choose the optimal product matches, product analysis methods are needed. Indeed, most of the known methods aim to analyze a product or one product family on the physical level. Different product families, however, may differ largely in terms of the number and nature of components. This fact impedes an efficient comparison and choice of appropriate product family combinations for the production system. A new methodology is proposed to analyze existing products in view of their functional and physical architecture. The aim is to cluster these products in new assembly oriented product families for the optimization of existing assembly lines and the creation of future reconfigurable assembly systems. Based on Datum Flow Chain, the physical structure of the products is analyzed. Functional subassemblies are identified, and a functional analysis is performed. Moreover, a hybrid functional and physical architecture graph (HyFPAG) is the output which depicts the similarity between product families by providing design support to both, production system planners and product designers. An illustrative example of a nail-clipper is used to explain the proposed methodology. An industrial case study on two product families of steering columns of thyssenkrupp Presta France is then carried out to give a first industrial evaluation of the proposed approach.
Energies, 2021
The present methodological study aims to assess boundary layer ingestion (BLI) as a promising met... more The present methodological study aims to assess boundary layer ingestion (BLI) as a promising method to improve propulsion efficiency. BLI utilizes the low momentum inflow of the wing or fuselage boundary layer for thrust generation in order to minimize the required propulsive power for a given amount of thrust for wing or fuselage-embedded engines. A multi-segment parallel compressor model (PCM) is developed to calculate the power saving from full annular BLI as occurring at a fuselage tail center-mounted aircraft engine, employing radially subdivided fan characteristics. Applying this methodology, adverse effects on the fan performance due to varying inlet distortions depending on flight operating point as well as upstream boundary layer suction can be taken into account. This marks one step onto a further segmented PCM model for general cases of BLI-induced inlet distortion and allows the evaluation of synergies between combined BLI and active laminar flow control as a drag reduc...
Aerospace, 2021
High aspect ratio aircraft have a significantly reduced induced drag, but have only limited insta... more High aspect ratio aircraft have a significantly reduced induced drag, but have only limited installation space for control surfaces near the wingtip. This paper describes a multidisciplinary design methodology for a morphing aileron that is based on pressure-actuated cellular structures (PACS). The focus of this work is on the transient dynamic system behavior of the multi-functional aileron. Decisive design aspects are the actuation speed, the resistance against external loads, and constraints preparing for a future wind tunnel test. The structural stiffness under varying aerodynamic loads is examined while using a reduced-order truss model and a high-fidelity finite element analysis. The simulations of the internal flow investigate the transient pressurization process that limits the dynamic actuator response. The authors present a reduced-order model based on the Pseudo Bond Graph methodology enabling time-efficient flow simulation and compare the results to computational fluid d...
Aerospace, May 25, 2018
Reducing losses in the secondary air system of gas and steam turbines can significantly increase ... more Reducing losses in the secondary air system of gas and steam turbines can significantly increase the efficiency of such machines. Meanwhile, brush seals are a widely used alternative to labyrinth seals. Their most valuable advantage over other sealing concepts is the very small gap between the sealing package and the rotor and thus reduced leakage mass flow. This small gap can be achieved due to the great radial flexibility without running the risk of severe detrimental deterioration in case of rubbing. Rubbing between rotor and seal during operation might occur as a result of e.g., an unequal thermal expansion of the rotor and stator or a rotor elongation due to centrifugal forces or manoeuvre forces. Thanks to the flexible structure of the brush seal, the contact forces during a rubbing event are reduced; however, the frictional heat input can still be considerable. Particularly in aircraft engines with their thin and lightweight rotor structures, the permissible material stresses can easily be exceeded by an increased heat input and thus harm the engine's integrity. The geometry of the seal has a decisive influence on the resulting contact forces and consequently the heat input. This paper is a contribution to further understand the influence of the geometrical parameters of the brush seal on the heat input and the leakage during the rubbing of the seal on the rotor. In this paper, a total of three seals with varied back plate inner diameter are examined in more detail. The experimental tests were carried out on the brush seal test rig of the Institute of Thermal Turbomachinery (ITS) under machine-relevant conditions. These are represented by pressure differences of 1 to 7 bar, surface speeds of 30 to 180 m/s and radial interferences of 0.1 to 0.4 mm. For a better interpretation, the results were compared with those obtained at the static test rig of the Institute of Jet Propulsion and Turbomachinery (IFAS) at the Technical University of Braunschweig. The stiffness, the blow-down and the axial behaviour of the seals as a function of the differential pressure can be examined at this test rig. It could be shown that the back plate inner diameter has a decisive influence on the overall operating behaviour of a brush seal.
Energies, 2018
Boundary layer ingestion is a promising method to decrease the propulsive power consumption of an... more Boundary layer ingestion is a promising method to decrease the propulsive power consumption of an aircraft, and therefore the fuel consumption. This leads to a reduced environmental impact and an improved cost-efficiency. To get a better understanding of this method and to estimate its benefits, the modelling of a propulsor located at the upper rear centerbody of a blended wing body aircraft is presented in this paper. A parallel compressor model approach is used to analyse the impact of the ingested low velocity fluid which leads to a non-uniform inflow. The required boundary layer data are generated with an analysis tool for 2D subsonic airfoils. Some parameter variations are conducted with the developed programme to study their impact on the power saving potential. In addition, a simple estimation for the benefit of embedded aeroengines is given. Despite the drawback from fan efficiency due to the inflow distortion, the results show a significant decrease in required propulsive power for boundary layer ingestion in combination with integrated engines.
Proceedings of Global Power & Propulsion Society, 2019
The impact of a deteriorated high-pressure compressor in a bypass jet propulsion engine is invest... more The impact of a deteriorated high-pressure compressor in a bypass jet propulsion engine is investigated and simulated in this paper by using a pseudo bond graph approach. This theory is realised in the in-house software tool ASTOR (AircraftEngine Simulation of Transient Operation Research) to simulate the performance of a jet engine in a transient load case with dynamic and individual volumes. Furthermore, experimental test data of a pass off test run from idle and takeoff stationary operating points of the used in-house turbofan engine V2500-A1 are analysed and compared to the performance model's results. The engine blades are in a deteriorated state for the test run. In ASTOR, two cases are considered for modelling the V2500. They only differ in the use of either a new or a deteriorated high-pressure compressor to analyse their influence on overall performance. In general, the deviations between both ASTOR cases and experimental data are smaller with a deteriorated compare to the new HPC in the stationary operating points. However, some of the occurring effects can be explained with the components that remained unchanged within the model. In the transient load case, which is simulated in ASTOR, the performance of the deteriorated model shows an increase of the transient peaks of the exhaust gas temperature of up to 5 %. In a nutshell, the HPC of a performance digital twin of a new V2500-A1 is replaced by for a deteriorated HPC of the in-house engine to investigate the influence on overall performance as well as to compare the results to the real jet engine in stationary operating points. With this information an earlier recognition of the deteriorated component is possible during maintenance, repair and overhaul (MRO) events. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License CC-BY-NC-ND 4.0
To reduce the specific fuel consumption of future turbofan engines via increased propulsion effic... more To reduce the specific fuel consumption of future turbofan engines via increased propulsion efficiency, the bypass ratio is increased by lowering the fan hub-to-tip ratio. Based on a comparison of fan configurations for an ultrahigh bypass ratio (UHBR) engine the effects of an increasing bypass ratio on the downstream near hub flow are presented. In order to evaluate the increasing amount of near hub flow associated with a reduced fan hub-to-tip ratio, the splitter is lowered at radial height. Numerical simulations of three different UHBR configurations of the fan were conducted and compared with fan configurations of the V2500 fan rotor. The results of the numerical flow simulations show, that the near hub flow is dominated by secondary flow effects. By increasing the bypass ratio, the fan wake is affected negligibly for both fan configurations. The interaction of the secondary flow and the core stator of the UHBR fan, combined with a reducing annulus cross section, is found to have a detrimental effect on the downstream stator. The findings of this paper provide a better understanding of the near hub flow sensitivities towards increasing bypass ratios of future turbofan engines.
Journal of the Global Power and Propulsion Society, 2018
Performance degradation due to wear of high pressure compressors (HPC) is a major concern in aero... more Performance degradation due to wear of high pressure compressors (HPC) is a major concern in aero-engine operation and maintenance. Among other effects especially erosion of airfoils leads to changed aerodynamic behavior and therefore to deterioration. These affects engine performance parameter like thrust specific fuel consumption (TSFC) and exhaust gas temperature (EGT). Reaching EGT-limit, the engine typically has to be overhauled during a shop visit to restore safety standards and performance. During state of the art shop visits, engines are repaired based on EGT-specifications. To further enhance the maintenance, tailored repairs for each jet engine based on engine history and operation conditions are necessary to take TSFC into account. To ensure such an effective maintenance, the aerodynamic behavior of deteriorated and repaired airfoils is the key factors. Therefore, geometric properties with high influence on aerodynamic performance have to be known. For blisks (BLade-Integ...
Journal of the Global Power and Propulsion Society, 2018
Today, main hub airports are already at their capacity limit and hence, smaller airports have bec... more Today, main hub airports are already at their capacity limit and hence, smaller airports have become more interesting for providing point-to-point connections. Unfortunately, the use of regional airports induces an increased environmental footprint for the population living around it. In an attempt to solve the related problems, the research project Coordinated Research Centre 880 aims to examine the fundamentals of a single-aisle aircraft with active high-lift configuration powered by two geared ultra-high bypass turbofan engines mounted over the wing. Low direct operating costs, noise shielding due to the over-wing configuration, and short runway lengths are the main advantages. Highlighting the performance, economical and noise benefits of a geared ultra-high bypass engine is the key aim of this paper. This assessment includes a correspondingly adjusted aircraft. Open literature values are applied to design the two investigated bypass ratios; a reference engine with a bypass rati...
The "Technische Universität Braunschweig" has commissioned a Propulsion Test Facility (PTF) for a... more The "Technische Universität Braunschweig" has commissioned a Propulsion Test Facility (PTF) for aspirated intake models of jet engines under off-design point conditions. For the commissioning of the unique facility, an aspirated intake test campaign has been carried out. Aim of the campaign was to compare the measured data in the PTF to numerical results and experimental data, which have already been measured in another test facility in the past using the same intake geometry. For the tests the Laminar Flow Reynolds Action (LARA) nacelle has been chosen. The LARA intake has been built and tested in the early 1990s at the "ONERA F1" wind tunnel during the work on hybrid laminar flow technology. At TU Braunschweig an Aspirated-Intake-Rig (ASI-Rig) with an in-house designed fan stage was worked out, whose fan is located far enough downstream to avoid interaction with the nacelle. For the results, the static pressure distribution at the inner and outer contour of the nacelle lip and the velocity distribution in the fan face during pure crosswind conditions have been compared and analysed. As seen in the results, the PTF pressure distribution at the lip is in good agreement with the numerical and the experimental data from the ONERA. Of particular note is the deviation between the achieved peak Mach number between the two experimental setups, analysed at the 0 • /180 • and 90 • section, which can be explained by the Reynolds number effect.
Energies, 2018
With the growth of aviation traffic and the demand for emission reduction, alternative fuels like... more With the growth of aviation traffic and the demand for emission reduction, alternative fuels like the so-called electrofuels could comprise a sustainable solution. Electrofuels are understood as those that use renewable energy for fuel synthesis and that are carbon-neutral with respect to greenhouse gas emission. In this study, five potential electrofuels are discussed with respect to the potential application as aviation fuels, being n-octane, methanol, methane, hydrogen and ammonia, and compared to conventional Jet A-1 fuel. Three important aspects are illuminated. Firstly, the synthesis process of the electrofuel is described with its technological paths, its energy efficiency and the maturity or research need of the production. Secondly, the physico-chemical properties are compared with respect to specific energy, energy density, as well as those properties relevant to the combustion of the fuels, i.e., autoignition delay time, adiabatic flame temperature, laminar flame speed and extinction strain rate. Results show that the physical and combustion properties significantly differ from jet fuel, except for n-octane. The results describe how the different electrofuels perform with respect to important aspects such as fuel and air mass flow rates. In addition, the results help determine mixture properties of the exhaust gas for each electrofuel. Thirdly, a turbine configuration is investigated at a constant operating point to further analyze the drop-in potential of electrofuels in aircraft engines. It is found that electrofuels can generally substitute conventional kerosene-based fuels, but have some downsides in the form of higher structural loads and potentially lower efficiencies. Finally, a preliminary comparative evaluation matrix is developed. It contains specifically those fields for the different proposed electrofuels where special challenges and problematic points are seen that need more research for potential application. Synthetically-produced n-octane is seen as a potential candidate for a future electrofuel where even a drop-in capability is given. For the other fuels, more issues need further research to allow the application as electrofuels in aviation. Specifically interesting could be the combination of hydrogen with ammonia in the far future; however, the research is just at the beginning stage.
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articles by Jens Friedrichs
Papers by Jens Friedrichs