The New York Times announced America's entry into the 'long awaited' Jet Age when a Pan American (Pan Am) World Airways Boeing 707 airliner left New York for Paris on October 26, 1958. Powered by four turbojet engines, the 707 offered speed, more nonstop flights, and a smoother and quieter travel experience compared to newly antiquated propeller airliners. With the Champs-Elysees only 6 hours away, humankind had entered into a new and exciting age in which the shrinking of the world for good was no longer a daydream. Fifty years later, the New York Times declared the second coming of a 'cleaner, leaner' Jet Age. Decades-old concerns over fuel efficiency, noise, and emissions shaped this new age as the aviation industry had the world poised for 'a revolution in jet engines'. Refined turbofans incorporating the latest innovations would ensure that aviation would continue to enable a worldwide transportation network. At the root of many of the advances over the preceding 50 years was the National Aeronautics and Space Administration (NASA). On October 1, 1958, just a few weeks before the flight of that Pan Am 707, NASA came into existence. Tasked with establishing a national space program as part of a Cold War competition between the United States and the Soviet Union, NASA is often remembered in popular memory first for putting the first human beings on the Moon in July 1969, followed by running the successful 30-year Space Shuttle Program and by landing the Rover Curiosity on Mars in August 2012. What many people do not recognize is the crucial role the first 'A' in NASA played in the development of aircraft since the Agency's inception. Innovations shaping the aerodynamic design, efficient operation, and overall safety of aircraft made NASA a vital element of the American aviation industry even though they remained unknown to the public. This is the story of one facet of NASA's many contributions to commercial, military, and general aviation: the development of aircraft propulsion technology, which provides the power for flight.

https://ntrs.nasa.gov/api/citations/20180003207/downloads/20180003207.pdf

The Power for Flight: NASA’s Contributions to Aircraft Propulsion

A review is presented of recent experimental results, analytical procedures and test techniques employed to evaluate the effects of inlet flow distortion on the stability characteristics of representative afterburning turbofan and turbojet compression systems. Circumferential distortions of pressure and temperature, separately and in combination are considered. Resulting engine sensitivity measurements are compared with predictions based on simplified parallel compressor models and with several distortion descriptor parameters.

/pdf/summary-of-recent-investigations-of-inlet-flow-distortion-ept1wx0zat.pdf

Summary of recent investigations of inlet flow distortion effect on engine stability

Detailed, accurate knowledge of interactions between embedded engines and inlet/ airframe-generated nonuniform flow profiles is essential for the successful design of robust integrated engine systems. In the absence of direct-connect experimentation, flow distortion patterns must be simulated by generating the nonuniformities with flow conditioning devices. Traditionally, wire screens installed on a supporting grid have been used to induce regions of steady total pressure distortions, utilizing sections of constant-porosity wire meshes assembled to form a complete screen. The design of wire screens that accurately reproduce steady total pressure distortions representing inlet-engine interactions is challenging because modern fluids and structures modeling approaches cannot be efficiently applied, resulting in numerous construction and testing iterations. Additive manufacturing methods (“rapid prototyping”) can be used to quickly and accurately produce distortion screens for testing of integrated inlet-engine systems. Rapid prototyping methods enable the production of unique screen geometries that are otherwise very difficult, impractical, or even impossible. A screen design method compatible with additive manufacturing methods that utilizes a hexagonal-element flow control grid composed of airfoil cross-sections is presented. Advantages of this new design and screen production method include improved aerodynamic and flow control features, a more durable structure, and greater design flexibility resulting in a more accurate reproduction of the desired distortion profile. Results of the design and fabrication of a prototype screen are presented.

Application of Additive Manufacturing to Rapidly Produce High-Resolution Total Pressure Distortion Screens

For distortion free steady state operation at the maximum (full afterburning) throttle position, the afterburner combustion efficiency decreased from 0.91 to 0.68 as engine inlet Reynolds number index was reduced from 0.80 to 0.25. Engine afterburner operational limits were obtained for transient and fixed throttle operation over a range of engine inlet distortions. At limiting conditions, time histories of pressures in the fan compressor during throttle transients between military and maximum showed the development of rotating stall in the fan hub which quickly propagated and produced complete stall in the high pressure compressor.

/pdf/experimental-evaluation-of-a-tf30-p-3-turbofan-engine-in-an-146yzq1mlq.pdf

Experimental evaluation of a TF30-P-3 turbofan engine in an altitude facility: Afterburner performance and engine-afterburner operating limits

Two variations of gas generator method to calculate thrust of afterburning turbofan engines installed in F-111A aircraft

/pdf/an-investigation-of-two-variations-of-the-gas-generator-42w963e284.pdf

An investigation of two variations of the gas generator method to calculate the thrust of the afterburning turbofan engines installed in an F-111A airplane

Performance and stall limits of afterburner-type turbofan engine with and without inlet flow distortion

M. Abdelwahab

Papers

Performance and stall limits of an afterburner-equipped turbofan engine with and without inlet flow distortion