Carlos Xisto

A pressure-based high resolution numerical method for resistive MHD

In the paper we describe in detail a numerical method for the resistive magnetohydrodynamic (MHD) equations involving viscous flow and report the results of application to a number of typical MHD test cases. The method is of the finite volume type but mixes aspects of pressure-correction and density based solvers; the algorithm arrangement is patterned on the well-known PISO algorithm, which is a pressure method, while the flux computation makes use of the AUSM-MHD scheme, which originates from density based methods. Five groups of test cases are addressed to verify and validate the method. We start with two resistive MHD cases, namely the Shercliff and Hunt flow problems, which are intended to validate the method for low-speed resistive MHD flows. The remaining three test cases, namely the cloud-shock interaction, the MHD rotor and the MHD blast wave, are standard 2D ideal MHD problems that serve to validate the method under high-speed flow and complex interaction of MHD shocks. Finally, we demonstrate the method with a more complex application problem, and discuss results of simulation for a quasi-bi-dimensional self-field magnetoplasmadynamic (MPD) thruster, for which we study the effect of cathode length upon the electromagnetic nozzle performance.

Ultra Low Emission Technology Innovations for Mid-century Aircraft Turbine Engines

Commercial transport fuel efficiency has improved dramatically since the early 1950s. In the coming decades the ubiquitous turbofan powered tube and wing aircraft configuration will be challenged by diminishing returns on investment with regards to fuel efficiency. From the engine perspective two routes to radically improved fuel efficiency are being explored; ultra-efficient low pressure systems and ultra-efficient core concepts. The first route is characterized by the development of geared and open rotor engine architectures but also configurations where potential synergies between engine and aircraft installations are exploited. For the second route, disruptive technologies such as intercooling, intercooling and recuperation, constant volume combustion as well as novel high temperature materials for ultra-high pressure ratio engines are being considered. This paper describes a recently launched European research effort to explore and develop synergistic combinations of radical technologies to TRL 2. The combinations are integrated into optimized engine concepts promising to deliver ultra-low emission engines. The paper discusses a structured technique to combine disruptive technologies and proposes a simple means to quantitatively screen engine concepts at an early stage of analysis. An evaluation platform for multidisciplinary optimization and scenario evaluation of radical engine concepts is outlined.

Aerodynamic and Aeroelastic Analysis of a Cycloidal Rotor

This work presents aerodynamic and aeroelastic models used to investigate the behaviorof a cycloidal rotor scaled for personal transportation applications. Three different modelsare considered. The impact of solidity on performance is evaluated using a two-dimensionalRANS viscous flow model with the boundary layer fully resolved. An aeroelastic multibodymodel is used to further evaluate the effects of aeroelasticity on the performance of therotor.

Modeling of hypersonic flow on a MPD thruster geometry using a PISO based method

In the following paper we intend to present some preliminary results for a self-field MPD thruster obtained with a new algorithm developed for solving the resistive magnetohydrodynamics (MHD) equations. The numerical method is based on the well known PISO algorithm and make use of AUSM-MHD scheme for flux calculation. The model is based on a single fluid approach and, in order to obtain a more realistic and stable solution, an equation of state for real gas is also included.

Parametric Analysis of a Large-scale Cycloidal Rotor in Hovering Conditions

In this work, four key design parameters of cycloidal rotors, namely the airfoil section; the number of blades; the chord-to-radius ratio; and the pitching axis location, are addressed. The four parameters, which have a strong effect on the rotor aerodynamic efficiency are analyzed with an analytical model and a numerical approach. The numerical method is based on a finite-volume discretization of two-dimensional Unsteady Reynolds Averaged Navier-Stokes equations on a multiple sliding mesh, are proposed and validated against experimental data. A parametric analysis is then carried out considering a large-scale cyclogyro, suitable for payloads above 100 kg, in hovering conditions. Results demonstrate that the airfoil thickness significantly affects the rotor performance; such a result is partly in contrast with previous findings for small- and micro-scale configurations. Moreover, it will be shown that increasing the number of blades could result in a decrease of the rotor efficiency. The effect of chord-to-radius will demonstrate that values of around 0.5 result in higher efficiency. Finally it is found out that for these large systems, in contrast with micro-scale cyclogyros, the generated thrust increases as the pitching axis is located away from the leading edge, up to 35% of chord length. Further the shortcomings of using simplified analytical tools in the prediction of thrust and power in non-ideal flow conditions will be highlighted and discussed.

Assessment of CO2 and NOx emissions in intercooled pulsed detonation turbofan engines

In the present paper, the synergistic combination of intercooling with pulsed detonation combustion is analyzed concerning its contribution to NOxand CO2emissions. CO2is directly proportional to fuel burn and can, therefore, be reduced by improving specific fuel consumption and reducing engine weight and nacelle drag. A model predicting NOxgeneration per unit of fuel for pulsed detonation combustors, operating with jet-A fuel, is developed and integrated within Chalmers Universitys gas turbine simulation tool GESTPAN. The model is constructed using CFD data obtained for different combustor inlet pressure, temperature and equivalence ratio levels. The NOxmodel supports the quantification of the trade-off between CO2and NOxemissions in a 2050 geared turbofan architecture incorporating intercooling and pulsed detonation combustion and operating at pressures and temperatures of interest in gas turbine technology for aero-engine civil applications.

First and Second Law Analysis of Radical Intercooling Concepts

An exergy framework was developed taking into consideration a detailed analysis of the heat exchanger (intercooler) component irreversibilities. Moreover, it was further extended to include an adequate formulation for closed systems, e.g. a secondary cycle, moving with the aircraft. Afterwards the proposed framework was employed to study two radical intercooling concepts. The first proposed concept uses already available wetted surfaces, i.e. nacelle surfaces, to reject the core heat and contribute to an overall drag reduction. The second concept uses the rejected core heat to power a secondary organic Rankine cycle and produces useful power to the aircraft-engine system. Both radical concepts are integrated into a high bypass ratio turbofan engine, with technology levels assumed to be available by year 2025. A reference intercooled cycle incorporating a heat exchanger in the bypass duct is established for comparison. Results indicate that the radical intercooling concepts studied in this paper show similar performance levels to the reference cycle. This is mainly due to higher irreversibility rates created during the heat exchange process. A detailed assessment of the irreversibility contributors, including the considered heat exchangers and the secondary cycle major components is made. A striking strength of the present analysis is the assessment of the component irreversibility rate and its contribution to the overall aero-engine losses.

An Outlook for Radical Aero Engine Intercooler Concepts

A state of the art turbofan engine has an overall efficiency of about 40%, typically composed of a 50% thermal and an 80% propulsive efficiency. Previous studies have estimated that intercooling may improve fuel burn on such an engine with a 3-5% reduction depending on mission length. The intercooled engine benefits stem firstly from a higher Overall Pressure Ratio (OPR) and secondly from a reduced cooling flow need. Both aspects relate to the reduced compressor exit temperature achieved by the intercooler action. A critical aspect of making the intercooler work efficiently is the use of a variable intercooler exhaust nozzle. This allows reducing the heat extracted from the core in cruise operation as well as reducing the irreversibility generated on the intercooler external surface which arises from bypass flow pressure losses. In this respect the improvements, higher OPR and lower cooling flow need, are achieved indirectly and not by directly improving the underlying thermal efficiency. This paper discusses direct methods to further improve the efficiency of intercooled turbofan engines, either by reducing irreversibility generated in the heat exchanger or by using the rejected heat from the intercooler to generate useful power to the aircraft. The performance improvements by using the nacelle wetted surface to replace the conventional intercooler surface is first estimated. The net fuel burn benefit is estimated at 1.6%. As a second option a fuel cooled intercooler configuration, operated during the climb phase, is evaluated providing a net fuel burn reduction of 1.3%. A novel concept that uses the rejected heat to generate additional useful power is then proposed. A secondary cycle able to convert rejected intercooler heat to useful thrust is used to evaluate three possible scenarios. The two first cases investigate the impact of the heat transfer rate on the SFC reduction. As a final consideration the geared intercooled engine cycle is re-optimized to maximize the benefits of the proposed heat recovery system. The maximum SFC improvement for the three cycles is established to 2%, 3.7% and 3%.

Numerical Computations of MHD Flow on Hypersonic and Re-Entry Vehicles

In hypersonic flight of reentry vehicles the radio blackout is a typical problem, in particular because it arises during a critical mission operation point. To mitigate this radio blackout the magnetic window concept is proposed. In this work a numerical model is presented to accurately simulate the effect of a magnetic field interacting with ionized plasma surrounding the vehicle. The numerical model is based on the MHD flow equations. Initially, the code is validated for pure hypersonic gas dynamics. Diverse high resolution spatial discretisation schemes, within a Finite Volume framework, are analyzed for robustness. Afterwards, the numerical code is further validated for MHD flows using the well-known Hartmann case. A very good comparison between numerical and analytical results is verified. This allows a proper validation of the method in terms of Lorentz force, in particular under low-magnetic Reynolds number conditions. A very tough test-case is finally computed, being typical of a reentry capsule geometry. The accuracy of the model is then verified for different applied magnetic fields.

3D Effects in Cyclorotor Propulsion Systems

A cycloidal propeller is an aircraft propulsion system that is composed by several blades rotating about a horizontal axis perpendicular to the flight direction. The rotor blades prescribe a periodic change on their pitch angle over a cycle of rotation. Many experimental, analytical and numerical studies have been developed in order to calculate force production and power required as well as the real simulation of the blades motion and the cyclorotor mechanical system operation. An important aspect of cycloidal propellers is the study of their efficiency both in hovering state and in forward motion considering 3D effects. For this purpose, it is developed a two-dimensional and three-dimensional CFD model of a cyclorotor whose blades describe the cycloidal path imposed by the pitch mechanical system control. Then, it is taken into account the experimental data for the proper validation. With the validated model, it presented and analyzed the 3D flow field around the cyclorotor under different operating conditions.Copyright