Suppression of Unwanted Noise and Howl in a Test Configuration Where Jet Exhaust is Discharged Into a Duct

John H. Glenn Research Center, Cleveland, Ohio

This technology is based on a model-scale experiment simulating a test facility where an engine exhaust is discharged into a duct. Such a configuration sometimes encounters unwanted noise in the form of high-amplitude spectral levels in certain frequency ranges or, in worst cases, a howl that can raise structural concern. The innovation involves placement of a velocity fluctuation damper at the end of the duct. Such a damper is shown to suppress not only the broadband unwanted noise, but also the howl when it occurs. Even though placing the damper on the upstream end of the duct works, the preferred location is the downstream end.

Posted in: Briefs, Propulsion, Noise, Noise, Exhaust pipes, Jet engines

Reynolds-Averaged Navier-Stokes Integration for Shock Noise (RISN)

Reynolds-averaged Navier-Stokes (RANS) Integration for Shock- Noise (RISN) is a computer program that evaluates acoustic analogies to predict jet noise. Jet noise is due to turbulence from the chaotic flow within the exhaust of a rocket or air-breathing jet engine. The source of jet noise is the turbulent mixing of the exhaust, screech (tones) due to a feedback loop between the semi-periodic shock cells and the nozzle, and broadband shockassociated noise due to the interaction of the turbulence with the shock cells. Acoustic analogies are rearrangements of the Navier-Stokes equations into a left-hand-side propagation operator and a right-hand-side equivalent noise source. RISN is capable of predicting the noise spectrum from all source components within supersonic offdesign jets. Furthermore, the noise from three-dimensional and axisymmetric nozzles can be predicted as long as a steady RANS solution is present. RISN predictions are based upon integrations of computational fluid dynamic solutions. Predictions consist of the spectral density at observers positioned around the nozzle exit.

Posted in: Briefs, Aerospace, Propulsion, Computational fluid dynamics, Computer software / hardware, Computer software and hardware, Computer software / hardware, Computer software and hardware, Noise, Noise, Jet engines

Regeneratively Cooled Porous Media Jacket

A non-toxic nitrous oxide fuel blend (NOFB) monopropellant with a high adiabatic flame temperature reaching and probably exceeding 3,450 K and a very high thermal decomposition limit (>390 °C) is under development. To design an optimal rocket engine that can handle the high adiabatic temperature during continuous rocket thruster operations, a regeneratively cooled rocket engine is desirable, but the regenerative jacket temperatures must remain well below the monopropellant’s thermal decomposition limit. In fact, the entire engine during operation should ideally remain well below the thermal ignition limit so that heat soak-back cannot potentially decompose the monopropellant following an engine restart.

Posted in: Briefs, Aerospace, Propulsion, Cooling, Rocket engines

Multi-Pulse Motor (MPM) Designed for Use with Electric Solid Propellants

The multi-pulse motor is a solid-propellant rocket motor that is able to produce a number of pulses for various thrust levels (5 to 30 pulses and thrusts between 0.25 and 1.5 N, depending on electric power delivery system) and can be turned on and off through the application of electrical power.

Posted in: Briefs, Aerospace, Propulsion, Solid propellants, Rocket engines

Adaptive Augmenting Control

Marshall Space Flight Center, Alabama

Adaptive augmenting control (AAC) is a forward gain, multiplicative adaptive algorithm for launch vehicle flight control that meets three summary-level design objectives: Do no harm — return to baseline control design when not needed; respond to errors in the ability of the vehicle to track commands to increase performance; and respond to undesirable parasitic dynamics (e.g., control-structure interaction) to maintain stability.

Posted in: Briefs, Propulsion, Adaptive control, Flight control systems, Adaptive control, Flight control systems, Launch vehicles

Servo Drive

Elmo Motion Control (Nashua, NH) offers the NANO Gold Twitter servo drive that delivers up to 4000 Watts of qualitative power, current up to 50A at 100VDC, and up to 15A/200V with advanced servo capabilities and support for EtherCAT or CANopen networking communication. It weighs 18 grams, is less than 13 cm3 in volume, and complies to safety, EMC, and environmental standards.

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Posted in: Products, Power Management, Manufacturing & Prototyping, Motion Control, Power Transmission

Pyramid Micro-Electrofluidic-Spray Propulsion Thruster with Integrated Attitude and Thrust Vector Control

NASA’s Jet Propulsion Laboratory, Pasadena, California

A micro-electrofluidic-spray propulsion (MEP) system was built on a micro scale, in which arrays of hundreds of nano-thrusters are etched on silicon wafers like ICs, only a centimeter on a side. Many dozens of these thruster chips can be arrayed to form a macro-thruster of finite and significant thrust. Approximately 300 centimeter-square, 100-micro-Newton micro-thrusters are arrayed in a square pyramidal structure. The pyramid is of shallow obliquity, with no more than 20° offset from the spacecraft face. This small angular offset is sufficient to provide thrust vector control (TVC) for the thruster.

Posted in: Briefs, Aerospace, Mechanical Components, Nanotechnology, Propulsion, Semiconductors & ICs

Evaluation of Rail Gun Technology for Launch Assist of Air-Breathing Rockets

John F. Kennedy Space Center, Florida

A prototype horizontal electromagnetic rail launcher has been demonstrated along with a corresponding theory. This system builds out of published work in augmented rail guns, but modifies this technology so that the motor can operate for seconds rather than milliseconds, and provide low acceleration (such as might be needed to launch an aircraft) rather than the extreme accelerations seen in the guns. The final system operates off of relatively low voltages (tens of volts), but with substantial currents. A lab bench prototype has been constructed and operated, demonstrating 13 Gs acceleration of a small 230-gram sled.

Posted in: Briefs, Aerospace, Motion Control, Motors & Drives, Propulsion, Aircraft, Launch vehicles

Using Harmonics to Control Flutter in Wings with Electrical Motors

This control system concept applies principles of forced aeroelasticity to distributed electric propulsion systems.

Armstrong Flight Research Center, Edwards, California

As aeronautics engineers develop innovative distributed electric propulsion systems, they face new challenges in ensuring that these innovative aircraft are safe as well as fuel efficient. In particular, these systems involve a large number of electrically driven fan motors mounted across a wing that induce vibrations that negatively affect the aircraft’s stability. These vibrations cause problems regardless of whether the motors are bottom-mounted, top-mounted, or wing-embedded.

Posted in: Briefs, Aeronautics, Motion Control, Motors & Drives, Propulsion, Vibration, Vibration, Electric motors, Fans

Micropulse Detonation Rocket Engine for Nano-Satellite Propulsion

Goddard Space Flight Center, Greenbelt, Maryland

An efficient propulsion system would use a micropulse detonation rocket engine (–PDRE) for nano-satellite maneuverability in space. Technical objectives are to design, build, and conduct a small detonation tube experiment in order to explore the feasibility of using –PDRE for propelling a nano-satellite. The plan is to study the requirement and predict the performance of –PDRE using various candidate propellants, as well as to conduct ground experiments, demonstrate useful thrust, and measure the specific impulse in a two-year time frame, so that a follow-on project can be proposed in a future NRI Center Innovation Fund.

Posted in: Briefs, TSP, Aeronautics, Motion Control, Propulsion, Automation, Propellants, Rocket engines, Satellites

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