Experimental Aerothermal Study of Internal Jet Engine Structures

In commercial aviation, efficiency improvements may be gained by aerodynamic optimisation of its structural components, such as the intermediate compressor duct (ICD) and the turbine rear structure (TRS). These components have frequently been overlooked in favour of compressor and turbine module optimisation. This means that publicly available information on these structural components is relatively sparse, even though such components may offer substantial weight reduction and, with the introduction of hydrogen as aviation fuel, novel synergistic component integration. This thesis presents heuristic solutions to meet modern demands for verification data on two commercial aviation engine components, the ICD and TRS. The work spans separate research projects and addresses both method development and test facility design. The development of two measurement methods is presented. First, detailed uncertainty analysis of multi-hole probe implementation in the TRS has led to a 50\% reduction in uncertainty regarding total pressure measurement. Furthermore, a modern approach to measuring convective heat transfer has been developed and implemented on the outlet guide vane in the TRS. Neither of the two approaches presented here is limited to applications in the TRS or ICD and may be used in other applications. The aerothermal performance of the TRS for two different Reynolds numbers, several flow coefficients and three different surface roughness numbers have been investigated, and novel results on transition location, streamlines, heat transfer and loss distribution are presented. The second part of the thesis describes the design of a new, low speed, 2.5 stage low-pressure compressor (LPC) facility, built to investigate novel concepts of hydrogen integration in the ICD. Methods developed in the TRS are adopted and implemented in the new facility. A pre-study of the LPC and ICD instrumentation shows that compressor performance may be measured with better than 1% uncertainty using gas path studies.Disclaimer:\ua0The content of this article reflects only the authors’ view. The Clean Sky 2 Joint Undertaking is not responsible for any use that may be made of the information it contains

Experimental Aerothermal Study on Internal Jet Engine Structures

For commercial aviation, one potential gain in efficiency can be found in the jet engine auxiliary modules, such as internal jet engine components. These components have historically largely been overlooked, prioritising units such as turbines or compressors. The publically available information for these auxiliary units is therefore relatively sparse even though they can enable substantial weight reduction and novel synergistic integration. The continuously increased fidelity of modern numerical tools poses a dilemma to the experimentalist. Higher accuracy and resolution are sought, but the accuracy of the experimentalist tools has stagnated.This thesis summarises instrumentation implemented methods in the Turbine Rear Structure(TRS). For the multi-hole probe and heat transfer measurement via IR-thermography a comprehensive uncertainty analysis and error mitigations are presented.The work presents a relatively high accuracy of 4% to 6% for the performed heat transfer studies on the outlet guide vane in the TRS. The presented implementation of the multi-hole probe in the TRS provides up to twice as high accuracy compared to conventional installation. Both approaches are general with few geometrical limitations and can be implemented on studies with similar ambient conditions.Two different Reynolds numbers, several flow-coefficients and three different surface roughness numbers have been investigated and novel results regarding transition location, streamline, heat transfer and loss distribution are presented in the attached papers

Infrared Thermography Investigation of Heat Transfer on Outlet Guide Vanes in a Turbine Rear Structure

Aerothermal heat transfer measurements in fluid dynamics have a relatively high acceptance of uncertainty due to the intricate nature of the experiments. The large velocity and pressure gradients present in turbomachinery application add further complexity to the measurement procedure. Recent method and manufacturing development has addressed some of the primary sources of uncertainty in these heat transfer measurements. However, new methods have so far not been applied in a holistic approach for heat transfer studies. This gap is bridged in the present study where a cost-effective and highly accurate method for heat transfer measurements is implemented, utilising infrared thermography technique (IRT) for surface temperature measurement. Novel heat transfer results are obtained for the turbine rear sturcture (TRS), at engine representative conditions for three different outlet guide vane (OGV) blade loading and at Reynolds Number of 235000. In addition to that, an extensive description of the implementation and error mitigation is presented

Conceptual Design of a Compressor Vane- HEX for LH2 Aircraft Engine Applications

In order to meet the ambitious environmental targets set by the Paris Agreement, new sustainable carbon neutral aviation fuels need to be introduced. The high gravimetry energy density of hydrogen, makes it a prime candidate for a future aviation fuel. However, the associated poor volumetric energy density, requires an increased aircraft volume and associated penalty in aerodynamic performance. The required volume occupied by the hydrogen fuel can be decreased in half, if stored in its liquid form. This however requires that the liquid hydrogen (LH2) is kept at cryogenic temperatures, requiring adequate tank insulation. Moreover, to increase the effective heating value of hydrogen, the fuel distribution system will include heat exchanger technology to increase the fuel temperature before injection in the combustion chamber. The present work provides an outlook of different heat exchanger technology for application in hydrogen fueled gas turbine aero engines. The heat exchangers can be placed in the vicinity of the engine to reject the heat generated by the gas core to the hydrogen fuel. Ideally, they are strategically located to use heat management to maximize the engine efficiency and ensuring sufficient component durability. Moreover, the combination of liquid hydrogen’s high specific heat with cryogenic storage temperatures results in a formidable cooling capacity that can be explored by more compact heat exchanger solutions

Experimental study on the low-pressure turbine wake interaction and development in the turbine rear structure

The aerodynamic characteristics of advanced turbine rear structures (TRSs) could be affected by the interaction between unsteady flow developed from low-pressure turbine (LPT) and outlet guide vanes (OGVs). Consequently, analyzing the details of the interactions between the rotor wakes, stator wakes and OGVs is essential to enhance the aerodynamic efficiency of the modern TRS. This paper presents time resolved flow field measurements in the TRS at engine representative flow conditions. Experiments were performed in an annular large-scale 1.5 stage turbine facility at Chalmers University of Technology, Laboratory of Fluid and Thermal Sciences. The facility provides engine-realistic boundary conditions for the TRS and experimental data were acquired using 5-hole and 7-hole probes (5HP and 7HP), hot-wire anemometry (HW) and Particle Image Velocimetry (PIV). The PIV and HW measurements were conducted for the first time to enhance the understanding of unsteady flow phenomena and to investigate the development of TRS inflow structures. The observed unsteady interaction mechanism between the rotor wakes, stator wakes and OGV is of prime interest and investigated in detail. The breakdown of rotor and stator wakes through the TRS are documented and the OGV wake is analysed in detail by PIV

Design of Chalmers new low-pressure compressor test facility for low-speed testing of cryo-engine applications

As a part of the ongoing Horizon 2020 ENABLEH2 project, a new low-speed compressor test facility is being constructed at the Chalmers University Laboratory of Fluids and Thermal Sciences. The ENABLEH2 project investigates critical technologies for cryogenic H2 applications in commercial aviation, including new combustion and heat management systems. This paper revolves around the design and construction of a core cooling flow facility which was commissioned to study and verify the potential benefits of incorporating a heat management system into the intermediate compressor duct (ICD).The test facility is designed to operate continuously at rotor midspan chord Reynolds number up to 600,000 to allow for detailed aerothermal studies at a technical readiness level four. The two-stage axial compressor is representative of the low-pressure compressor and ICD of a mid-size commercial jet engine. The compressor is powered by a 147kW electric motor at 1920 RPM. The mass-flow and pressure ratio are controlled by restricting valves located at the inlet of the facility. A compact volute settling chamber, with an integrated thermal control system is used to control the inlet temperature and remove flow non-uniformities downstream the restrictor valves before entering the compressor. At the compressor inlet, a turbulence mesh is mounted to increase the turbulence intensity levels to 3-4% at the leading edge of the variable inlet guide vanes. The compressor is mounted vertically to allow for easy access to the downstream ICD and mitigate non-axisymmetric mechanical loads. The compressor unit allows for optical and traverse access at two +- 9-degree sectors for all the rotor-stator interfaces. Upstream the OGV, there are four independent $\pm$ 180-degree access traverse systems. In the ICD, measurements are carried out by a single ABB robot with a U-shaped probe mount, providing full volume probing access of the ICD. At the first design iteration the ICD is designed to be instrumented with multi-hole probes, hot-wire anemometry and heat transfer measurement using IR-thermography.The paper describes the facility and the process of achieving a high case similarity (engine representative) while maximising the quality of the experimental data over a large test domain, targets that often produce conflicting design demands

Effect of heat exchanger integration in aerodynamic optimization of an aggressive S-duct

Intercooling the core flow in the compression process using bypass air can potentially reduce fuel consumption in commercial aviation. However, one of the critical challenges with intercooling is the installation and weight penalty due to complex ducting and large surface area for air-to-air heat exchangers (HEX). The recent interest in cryogenic hydrogen (LH2) as a potentially carbon-neutral fuel for commercial aviation expands the propulsivesystem’s design space due to the vastly different fuel properties between classical Jet-A and LH2. Regarding intercooling, LH2 adds a formidable heat sink with a high specific heat capacity and low storage temperature at 20K and, if utilised in the intercooling process, should allow for increased cooling power density with less installation penalties than an air-to-air HEX. Furthermore, the heat is transferred to the fuel instead of ejectedinto the bypass air which has potential thermodynamical benefits. The HEX can further be synergistically used to radial turn the core flow in the ICD.This paper presents the integration of a compact air-to-LH2 heat exchanger inside the gas path of the intermediate compressor duct (ICD) as the shape of a truncated cone. Axisymmetric numerical simulations areutilised to evaluate the duct performance and optimise hub and shroud lines for minimal pressure drop andoutlet uniformity. The HEX sizing was based on a preliminary system model of an LH2 commercial aviation engine with 70,000 lbs of thrust

Development of fuel and heat management systems for liquid hydrogen powered aircraft

The presentation describes the recent developments in the design of the fuel and heat management systems for liquid hydrogen powered aircraft within the H2020 project ENABLEH2. The fuel distribution system main task is to deliver the right amount of hydrogen to the combustion chamber at an adequate pressure. This requires the usage of fuel pumps, valves, insulated piping, and a fuel control system to adjust the fuel flow for a given engine rating. Moreover, since liquid hydrogen is stored at cryogenic temperatures (-253C), it also requires the integration of heat exchanger technology to increase the fuel temperature up to a state where it can be efficiently mixed with air and combusted. The combination of hydrogen high specific heat with cryogenic temperatures results in formidable cooling capacity that can be explored by compact heat-exchanger solutions. Concepts that use existing engine aero-surfaces located after rotating turbomachinery are currently being investigated a Chalmers University of Technology.\ua0 A recently commissioned facility to investigate the potential benefits of a compressor flow cooling heat rejection system will also be discussed.\ua0 The test facility comprises a vertically mounted low-speed 2.5 stage compressor designed to operate continuously at rotor mid-span chord Reynold number up to 600,000, which is representative of a large-size future geared turbofan engine. Detailed aerothermal studies at TRL4 will be conducted to calibrate in-house design methods for radical core integrated heat exchangers. The facility is driven by a 147kW electric drive at a nominal speed of 1920 RPM. Traverse access is included in two 18-degree sectors for all the rotor-stator interfaces. At the upstream plane of the compressor outlet-guide-vane, four independent access traverse systems are included for a 360-degree access. Downstream, an ABB robot arm with a U-shaped probe mount provides full volume probing access in the exit compressor duct

Experimental and Numerical Study of Laminar-Turbulent Transition on a Low-Pressure Turbine Outlet Guide Vane

This work presents an experimental and numerical investigation on the laminar-turbulent transition and secondary flow structures in a Turbine Rear Structure (TRS). The study was executed at engine representative Reynolds number and inlet conditions at three different turbine load cases. Experiments were performed in an annular rotating rig with a shrouded low-pressure turbine upstream of a TRS test section. The numerical results were obtained using the SST k–ω turbulence model and the Langtry- Menter γ–θ transition model. The boundary layer transition location at the entire vane suction side is investigated. The location of the onset and the transition length are measured using IR thermography along the entire vane span. The IR-thermography approach was validated using hot-wire boundary layer measurements. Both experiments and CFD show large variations of transition location along the vane span with strong influences from endwalls and turbine outlet conditions. Both correlate well with traditional transition onset correlations near midspan and show that the transition onset Reynolds number is independent of the acceleration parameter. However, CFD tends to predict an early transition onset in the midspan vane region and a late transition in the hub region. Furthermore, in the hub region, CFD is shown to overpredict the transverse flow and related losses.Disclaimer:\ua0The content of this article reflects only the authors’ view. The Clean Sky 2 Joint Undertaking is not responsible for any use that may be made of the information it contains

Numerical modeling of laminar-turbulent transition in an interconnecting compressor duct

With the purpose of meeting the ambitious environmental targets set by the European Union (EU) in 2019, after the European Green Deal, new sustainable fuels need to be adapted by the aviation industry. Hydrogen stands out to be a promising candidate due to its CO2-free combustion, and higher energy density compared to kerosene. The main disadvantages of LH2 are its lower density compared to kerosene and the required cryogenic storage temperature, which affects propellant feed system size, mass, and insulation requirements. Nevertheless, the cryogenic temperatures coupled with its high specific heat capacity makes LH2 a formidable coolant, of which engine precooling, intercooling, and recuperation are potentially beneficial applications for aero engines. The focus of this paper is on how to model the vane surfaces of an Intermediate Compressor Duct (ICD) using CFD for the purpose of intercooling to support and prepare for future validation work using the Chalmers low pressure compressor rig. This study will analyze the behavior of different CFD transition models in the prediction of laminar-turbulent transition, mesh dependency, the impact of wall temperature, and the effect of conduction in the vane material. CFD simulations using the Gamma-Theta and Intermittency transition models showed very similar results and highlighted the need of well-refined computational grids to reach mesh independence for pressure loss, heat flow, and transition onset and length. A parametric study where the vane wall temperatures were decreased showed that transition was delayed for decreasing wall temperatures and that the length of the transition zone decreased as well. The results of a conjugated CFD model of a cryogenically cooled ICD vane showed that using only the surface of the vane for exchanging heat led to a relatively small decrease in core air total temperature. Therefore, the merit of using the existing aerodynamic surfaces of the ICD for heat transfer needs to be investigated further by including the hub and shroud surfaces as well, or increasing surface area further by using fins