In this work, Rayleigh microwave scattering was utilized to measure the electron number density produced by nanosecond high voltage breakdown in air between two electrodes in a pin-to-pin configuration (peak voltage 26 kV and pulse duration 55 ns). The peak electron density decreased from 1•10 17 cm -3 down to 7•10 14 cm -3 when increasing the gap distance from 2 to 8 mm (total electron number decreased from 2•10 13 down to 5•10 11 respectively). Electron number density decayed on the timescale of about several s due to dissociative recombination.
A quasi-one-dimensional code previously developed for axial wave rotor channels with on-rotor combustion is now extended for curved and canted channels to study the physics of a wave rotor combustor turbine. The unsteady gas dynamics in a wave rotor channel provides pressure exchange through travelling waves. Having on-rotor combustion will provide compression, combustion and expansion in a single device. Additionally, having a curved or a canted profile allows energy transfer from the gas to the blade due to flow turning, resulting in reaction torque. Prior work on modeling curved and canted channels without combustion and on axial channels with combustion are used for code verification. NomenclatureTangential velocity component U B = Internal energy at state B U A = Internal energy at state A h = Enthalpy p = Pressure u x = Axial component of channel velocity u θ = Tangential component of channel velocity F B = Momentum source term F C = Source term for blade stress Q C = Source term for heat flux S = Channel cross-sectional area = Channel length = Channel width (related to opening time) ̇ = Mass flow rate β = Blade angle ρ = Density Ω = Angular Velocity = Mean line radius χ = Source Vector
Aircraft with parallel hybrid architecture have the potential of significantly reducing fuel burn, if the flight mission is planned consistent with optimization of propulsive components in the integrated system. While purely electric drive may continue to evolve for unmanned and manned light aircraft on short missions, electrical drive may too heavy or lacking energy to power a large transport aircraft on a long flight. This has lead to the development of architectures where most parts of the mission are operated with a combination electric and gas turbine power. Judicious application of electric drive in specific phases of the flight mission may help reduce overall fuel burn and the size of the gas turbine engine. A simplified fuel burn calculation for an aircraft mission provides a first order approximate of power split between electric and gas turbine. The method is intended for use in sizing a gas turbine engine that would provide significant reduction in fuel burn.
Wave rotors are periodic-flow devices that provide dynamic pressure exchange and efficient energy transfer through internal pressure waves generated due to fast opening and closing of ports. Wave turbines are wave rotors with curved channels that can produce shaft work through change of angular momentum from inlet to exit. In the present work, conservation equations with averaging in the transverse directions are derived for wave turbines, and quasi-one-dimensional model for axial-channel non-steady flow is extended to account for blade curvature effects. The importance of inlet incidence is explained and the duct angle is optimized to minimize incidence loss for a particular boundary condition. Two different techniques are presented for estimating the work transfer between the gas and rotor due to flow turning, based on conservation of angular momentum and of energy. The use of two different methods to estimate the shaft work provides confidence in reporting of work output and confirms internal consistency of the model while it awaits experimental data for validation. The extended wave turbine model is used to simulate the flow in a three-port wave rotor. The work output is calculated for blades with varying curvature, including the straight axial channel as a reference case. The dimensional shaft work is reported for the idealized situation where all loss-generating mechanisms except flow incidence are absent, thus excluding leakage, heat transfer, friction, port opening time, and windage losses. The model developed in the current work can be used to determine the optimal wave turbine designs for experimental investment.
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