With the increased emphasis on both reliability and multi-functionality in the aerospace industry, active materials are fast becoming an enabling technology capturing the attention of an increasing number of engineers and scientists worldwide. This article reviews the class of active materials known as shape memory alloys (SMAs), especially as used in aerospace applications. To begin, a general overview of SMAs is provided. Their useful properties and engineering effects are described and the methods in which these may be utilized are discussed. A review of past and present aerospace applications is presented. The discussion addresses applications for both atmospheric earth flight as well as space flight. To complete the discussion, SMA design challenges and methodologies are addressed and the future of the field is examined.

https://journals.sagepub.com/doi/pdf/10.1243/09544100JAERO211

Aerospace applications of shape memory alloys

A shape memory alloy (SMA) with a composition of Ni60Ti40 (wt%) was chosen for the fabrication of active beam elements intended for use as cyclic actuators and incorporated into a morphing aerospace structure. The active structure is a variable-geometry chevron (VGC) designed to reduce jet engine noise in the take-off flight regime while maintaining efficiency in the cruise regime. This two-part work addresses the training, characterization and derived material properties of the new nickel-rich composition, the assessment of the actuation properties of the active beam actuator and the accurate analysis of the VGC and its subcomponents using a model calibrated from the material characterization. The characterization performed in part I of this work was intended to provide quantitative information used to predict the response of SMA beam actuators of the same composition and with the same heat treatment history. Material in the form of plates was received and ASTM standard tensile testing coupons were fabricated and tested. To fully characterize the material response as an actuator, various thermomechanical experiments were performed. Properties such as actuation strain and transformation temperatures as a function of applied stress were of primary interest. Results from differential scanning calorimetry, monotonic tensile loading and constant stress thermal loading for the as-received, untrained material are first presented. These show lower transformation temperatures, higher elastic stiffnesses (60–90 GPa) and lower recoverable transformation strains (≈1.5%) when compared to equiatomic NiTi (Nitinol). Stabilization (training) cycles were applied to the tensile specimens and characterization tests were repeated for the stable (trained) material. The effects of specimen training included the saturation of cyclically generated irrecoverable plastic strains and a broadening of the thermal transformation hysteresis. A set of final derived material properties for this stable material is provided. Finally, the actuation response of a structural beam component composed of the same material given the same thermomechanical processing conditions was assessed by applying a constant bias load and a variable bias load as thermal actuation cycles were imposed.

https://iopscience.iop.org/article/10.1088/0964-1726/19/1/015020/pdf

Use of a Ni60Ti shape memory alloy for active jet engine chevron application: I. Thermomechanical characterization

Research on Pulse Detonation Combustion Systems: A Status Report

The continuous detonation engine (CDE) is based on detonation waves and is a new jet engine concept that is expected to bring a technical revolution to current aviation and aerospace propulsion sys...

Recent Progress, Development Trends, and Consideration of Continuous Detonation Engines

A multitube pulse detonation combustor consisting of eight unvalved tubes arranged in a can-annular configuration was integrated with a single-stage axial turbine nominally rated for 10 lbm=s, 25,000 rpm and 1000 hp. The multitube pulse-detonation-combustor-turbine hybrid was operated using ethylene-air mixtures for runs of 5 min to achieve thermal steady state in order to quantify performance at two operating conditions using simultaneous and sequential firing patterns. Analysis of these data reveal that turbine efficiency under pulsedetonation-combustor-fired operation was indistinguishable from steady performance within the 8 points measurement uncertainty. Furthermore, the pulse-detonation-combustor-turbine hybrid system demonstrated a potential 25% improvement in efficiency once corrections were made for the suboptimal fueling design, which resulted in lower-than-anticipated combustion efficiency. The present work is promising as it suggests that a pulsedetonation-combustor-turbine hybrid engine performance benefit can be realized with further development.

Experimental Investigations of the Performance of a Multitube Pulse Detonation Turbine System

Experimental studies were carried out to investigate the performance of a hybrid propulsion system integrating an axial flow turbine with multiple pulse detonation combustors. The integrated system consisted of a circular array of six pulse detonation combustor (PDC) tubes exhausting through an axial flow turbine. Turbine component performance was quantified by measuring the amount of power generated by the turbine section. Direct comparisons of specific power output and turbine efficiency between a PDC driven turbine and a turbine driven by a traditional steady flow combustor were made. It was found that the PDC driven turbine had comparable performance to that of a steady burner driven turbine across the operating map of the turbine.

Performance of an Axial Flow Turbine Driven by Multiple Pulse Detonation Combustors

Performance Measurements of a Pulse Detonation Combustor Array Integrated with an Axial Flow Turbine

*† ‡ Peak pressure attenuation data is presented for pulse detonation combustor (PDC) firing into a single stage axial flow turbine. Cases are presented for both single PDC tubes and for an annular array of six PDC tubes. Pressure attenuation is characterized for a wide array of PDC operating parameters, including fill fraction, equivalence ratio, nitrogen dilution percentage, and firing frequency. Effects of additional cold air flow mixed into the PDC exhaust prior to the turbine inlet are also quantified. It is shown that certain PDC operating conditions lead to a maximum peak pressure attenuation, which should correspond to the greatest energy extraction by the turbine from the PDC exhaust flow.

Acoustic Interactions of a Pulse Detonation Engine Array with a Gas Turbine

An experimental investigation on the directivity of acoustic emissions from a pulse detonation engine (PDE) was performed in an anechoic facility using a circular array of eight microphones (62 to 167 deg). The acoustic pressure-time traces for the baseline configuration were observed to be composed of an impulsive shock followed by a fast transient decay to ambient conditions. The spectra were characterized by a fundamental broadband distribution in the low frequency range of less than 1 kHz and a 20dB/decade decay rate at frequencies greater than 10 kHz. The higher frequency content is a result of the impulse source of the PDE blast-wave, while the fundamental mode was attributed to the approximate 1 to 2 ms transient following the blast-wave. The PDE operating conditions were systematically varied during the tests to quantify their effects on the acoustic emissions. The results showed an increase in OASPL with fill-fraction and a logarithmic increase with PDE cycle frequency. Fill-fraction was found to be an appropriate parameter for normalizing PDE acoustic data from different detonation tube lengths. In addition, three modes of operation of the PDE were also identified based on the value of fill-fraction. The sensitivity of the PDE acoustic levels to exhaust nozzle geometry was also studied. A converging nozzle showed global reduction in OASPL at all fill-fractions, while diverging nozzles experienced OASPL reductions in only the downstream angles. The results suggest that the acoustic levels were sensitive to both the nozzle length and area ratio, and it was observed that this sensitivity changed with fillfraction.

Acoustic measurements of a pulse detonation engine

A rig has been designed to integrate an annular array of six pulse detonation engines (PDEs) with a common gas turbine engine. The purpose of this rig is to allow for the examination of the acoustic and performance effects of such integration. The overall effect of this combination is a more compact, simplified engine concept whereby the core (the high pressure compressor, combustor, and high pressure turbine) of a typical gas turbine engine is replaced by the PDE tubes, and combustion occurs in an unsteady manner instead of that which comes from typical steady flow combustors. Success in such integration would result in a more efficient form of combustion that would use less fuel while reducing the weight and cost of the engine dramatically. This paper describes the design of the integration rig, and presents some preliminary pressure history results based on the flow inside the PDE tube, inside the rig itself, and the flow downstream of the turbine to provide an understanding of the behavior of the PDE flow passing through the blades of the turbine.

Aaron Glaser

Papers

Performance of an Axial Flow Turbine Driven by Multiple Pulse Detonation Combustors

Performance Measurements of a Pulse Detonation Combustor Array Integrated with an Axial Flow Turbine

Acoustic Interactions of a Pulse Detonation Engine Array with a Gas Turbine

Acoustic measurements of a pulse detonation engine

Acoustic Measurements of an Integrated Pulse Detonation Engine with Gas Turbine System