Cubesats: Cost-effective science and technology platforms for emerging and developing nations

An exothermic chemical reaction coupled with a one-dimensional conductor has been predicted to give rise to self-propagating waves with high thermal conductivity. This is now demonstrated experimentally with carbon nanotubes used as guides for the waves, which propagate with high thermal conductivity and with electric pulses of very intense power.

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Chemically driven carbon-nanotube-guided thermopower waves

Positive polarity nanosecond pulse driven dielectric barrier discharge (ns-DBD) plasma actuators are studied experimentally in quiescent atmosphere. Pulse energy and instantaneous pulse power (hereafter referred to as energy and power) are calculated using simultaneous voltage and current measurements. Electrical characteristics are evaluated as a function of peak voltage, pulse frequency, discharge length, and dielectric thickness. Schlieren imaging is used to provide a relative estimate of discharge energy that is coupled to the near surface gas as heat for the same parameters. Characteristics of the DBD load have a substantial effect on the individual voltage and current traces which are reflected in the energy and power values. Power is mainly dependent on actuator length which is inconsistent with schlieren data as expected. Higher per unit length energy indicates a stronger compression wave for a given actuator geometry, but this is not universally true across different actuators suggesting some constructions more efficiently couple energy to the gas. Energy and compression wave strength are linearly related. Higher pulse frequency produces higher energy but is primarily attributed to heating of the actuator and power supply components and not to an optimal discharge frequency. Both energy and wave strength increase as peak voltage to the power of approximately 3.5 over a substantial range similar to ac-DBD plasma actuators.

Characterization of nanosecond pulse driven dielectric barrier discharge plasma actuators for aerodynamic flow control

Nanosecond pulse discharge plasma imaging, coupled pulse energy measurements, and kinetic modeling are used to analyze the mechanism of energy coupling in high repetition rate, spatially uniform, nanosecond pulse discharges in air in plane-to-plane geometry. Under these conditions, coupled pulse energy scales nearly linearly with pressure (number density), with energy coupled per molecule being nearly constant, in good agreement with the kinetic model predictions. In spite of high-peak reduced electric field reached before breakdown, E/N ∼ 500–700 Td, the reduced electric field in the plasma after breakdown is much lower, E/N ∼ 50–100 Td, predicting that a significant fraction of energy coupled to the air plasma, up to 30–40%, is loaded into nitrogen vibrational mode.A self-similar, local ionization kinetic model predicting energy coupling to the plasma in a surface ionization wave discharge produced by a nanosecond voltage pulse has been developed. The model predicts key discharge parameters such as ionization wave speed and propagation distance, electric field, electron density, plasma layer thickness, and pulse energy coupled to the plasma, demonstrating good qualitative agreement with experimental data and two-dimensional kinetic modeling calculations. The model allows an analytic solution and lends itself to incorporation into existing compressible flow codes, at very little computational cost, for in-depth analysis of the nanosecond discharge plasma flow control mechanism. The use of the model would place the main emphasis on coupling of localized thermal perturbations produced by the discharge with the flow via compression waves and would provide quantitative insight into the flow control mechanism on a long time scale.

https://iopscience.iop.org/article/10.1088/0963-0252/22/1/015013/pdf

Measurements and kinetic modeling of energy coupling in volume and surface nanosecond pulse discharges

The efficacy of a single dielectric barrier discharge plasma actuator for controlling turbulent boundary-layer separation from the deflected flap of a high-lift airfoil is investigated between Reynolds numbers of 240,000 (15 m/s) and 750,000 (45 m/s). Momentum coefficients for the dielectric barrier discharge plasma actuator are approximately an order of magnitude lower than those usually employed for such studies, yet control authority is still realized through amplification of natural vortex shedding from the flap shoulder, which promotes momentum transfer between the freestream and separated region. This increases dynamic loading on the flap and further organizes turbulent fluctuations in the wake. The measured lift enhancement is primarily due to upstream effects from increased circulation around the entire model, rather than full reattachment to the deflected flap surface. Lift enhancement via instability amplification is found to be relatively insensitive to changes in angle of attack, provided that the separation location and underlying dynamics do not change. The modulation waveform used to excite low-frequency perturbations with a high-frequency plasma-carrier signal has a considerable effect on the actuator performance. Control authority decreases with increasing Reynolds number and flap deflection, highlighting the necessity for further improvement of plasma actuators for use in realistic takeoff and landing transport aircraft applications. These findings are compared to studies on a similar high-lift platform using piezoelectric-driven zero-net-mass flux actuation.

High-lift airfoil separation with dielectric barrier discharge plasma actuation

A model for the propulsion system of a small-scale electric Unmanned Aircraft System (UAS) is presented. This model is based on a Blade Element Momentum (BEM) model of the propeller, with corrections for tip losses, Mach effects, three-dimensional flow components, and Reynolds scaling. Particular focus is placed on the estimation of scale effects not commonly encountered in the full-scale application of the BEM modeling method. Performance predictions are presented for geometries representative of several commercially available propellers. These predictions are then compared to experimental wind tunnel measurements of the propellers’ performance. The experimental data supports the predictions of the proposed BEM model and points to the importance of scale effects on prediction of the overall system performance.

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Blade Element Momentum Modeling of Low-Re Small UAS Electric Propulsion Systems

A model for the propulsion system of a small-scale electric unmanned aerial system is presented. This model is based on a blade element momentum (BEM) model of the propeller, with corrections for tip losses, Mach effects, three-dimensional flow components, and Reynolds scaling. Particular focus is placed on the estimation of scale effects not commonly encountered in the full-scale application of the BEM modeling method. Performance predictions are presented for geometries representative of several commercially available propellers. These predictions are then compared with experimental wind tunnel measurements of the propellers’ performance. The experimental data support the predictions of the proposed BEM model and point to the importance of scale effects on prediction of the overall system performance.

Blade Element Momentum Modeling of Low-Reynolds Electric Propulsion Systems

A phenomenological model, suitable for coupling to Large Eddy Simulations (LES) of flow control applications, is developed to simulate the effects of a nanosecond dielectric barrier discharge (NS-DBD) actuator. The model considers various surface and volume heating profiles to reproduce the key qualitative and quantitative features of NSDBD actuators. The model is tuned to match the unique wave shape observed in Schlieren imagery and quantitative wave speed and displacement data. The induced wave structure, comprised of a cylindrical component with a tail, can be reproduced with a spatially varying heating distribution – a Gaussian variation in the direction of the discharge provides accurate results. The instantaneous location of the wave, which propagates at approximately acoustic speed after an initial transient may be matched by considering a volumetric deposition model. Power input estimates in the current model are consistent with those postulated in experimental investigations.

A Semi-Empirical Model of a Nanosecond Pulsed Plasma Actuator for Flow Control Simulations with LES

For most orbital maneuvers, small satellites weighing less than 10 kg require propulsion systems capable of producing thrust in the micro-Newton to milli-Newton force range. At this scale, electrokinetic (EK) pumping offers a method to precisely meter liquid propellants under purely electrical control at pressures and flow rates well-suited for microthruster applications. After exploring a variety of materials and surface treatments for the electrokinetic pumping media, we have demonstrated EK pumping of anhydrous hydrazine using both packed-capillary and larger sintered-monolith pump designs. Hydrogen peroxide has proven difficult to directly pump electrokinetically, but we have shown the utility of delivering peroxide and other electrokinetically incompatible liquids indirectly using in-line reservoirs with fluidic isolation to separate the pump working fluid from the propellant. Directly- and indirectly-pumped propellants have been delivered to novel capillary microthrusters with integrated catalyst beds and plasma-formed micronozzle structures. Specific impulses up to 190 s have been shown for hydrazine in non-optimized capillary thrusters at a mass flow rate of 1.5 mg/s. Controlled thrust pulses with a maximum continuous thrust of 1.5 mN, minimum impulse bit of 7 μN-s, and average specific impulse of 110 s have been demonstrated with the electrokinetically pumped microthruster assembly.

Electrokinetic pumping of liquid propellants for small satellite microthruster applications

Detect and Avoid (DAA) systems are complex communication and locational technologies comprising multiple independent components. DAA technologies support communications between ground-based and space-based operations with aircraft. Both manned and unmanned aircraft systems (UAS) rely on DAA communication and location technologies for safe flight operations. We examined the occurrence and duration of communication losses between radar and automatic dependent surveillance–broadcast (ADS-B) systems with aircraft operating in proximate airspace using data collected during actual flight operations. Our objectives were to identify the number and duration of communication losses for both radar and ADS-B systems that occurred within a discrete time period. We also investigated whether other unique communication behavior and anomalies were occurring, such as reported elevation deviations. We found that loss of communication with both radar and ADS-B systems does occur, with variation in the length of communication losses. We also discovered that other unexpected behaviors were occurring with communications. Although our data were gathered from manned aircraft, there are also implications for UAS that are operating within active airspaces. We are unaware of any previously published work on occurrence and duration of communication losses between radar and ADS-B systems.

Matthew McCrink

Papers

Blade Element Momentum Modeling of Low-Re Small UAS Electric Propulsion Systems

Blade Element Momentum Modeling of Low-Reynolds Electric Propulsion Systems

A Semi-Empirical Model of a Nanosecond Pulsed Plasma Actuator for Flow Control Simulations with LES

Electrokinetic pumping of liquid propellants for small satellite microthruster applications

Analysis of Radar and ADS-B Influences on Aircraft Detect and Avoid (DAA) Systems