Martin Brouillette

Microscale Shock Tube

This paper reports on the design, microfabrication, characterization, and testing of the first instrumented micrometer-scale shock tube. This device was fabricated by a series of etching, deposition, and patterning processes of the different structural layers on a silicon substrate to first create an array of direct-sensing piezoelectric pressure sensors followed by the bonding of another substrate to create a microchannel. The resulting assembly is a rectangular channel with a hydraulic diameter of 34 μm and a length of 2000 μm, instrumented with five wall pressure sensors along its length. This device is used to characterize, for the first time, the propagation of shock waves at microscales, where transport effects such as wall friction and heat transfer are important. The results show shock-wave attenuation along the length of the microchannel in accordance with simple analytical models for these flows.

Rim-Rotor Rotary Ramjet Engine, Part 2: Quasi-One-Dimensional Aerothermodynamic Design

The rim–rotor rotary ramjet engine is a new propulsion-system design with the potential to significantly improve power density and reduce complexity over conventional gas turbines, thus making it an interesting alternative for future transportation and stationary power systems. This paper presents a quasi-one-dimensional aerothermodynamic design model, taking into account the dominant physics of the rim–rotor rotary ramjet engine: 1) shock-wave compression, 2) high-g field combustion, 3) viscous losses, 4) heat transfer, 5) inlet and outlet periodic condition, and 6) windage losses. It is shown that high flame velocity due to buoyant forces leads to a very compact combustion chamber and possibly very low nitrogen oxides. A 500 kW rim–rotor rotary-ramjet-engine version is designed with the model and could produce 7:6 kW=kg at a tangential velocity of 1000 m=s, which is more than twicetheactualgas-turbinepowerdensity.Aproof-of-conceptprototypeistestedatlowspeed(Mach1),andshows good agreement with the model for both indicated power without combustion and windage losses. Combustion efficiency is measured to over 85% at 220;000g. These results confirm the design model capabilities, at least within the range of tested Mach numbers.

Design and Experimental Validation of a Supersonic Concentric Micro Gas Turbine

This paper presents the design and experimental results of a new micro gas turbine architecture exploiting counterflow within a single supersonic rotor. This new architecture, called the supersonic rim-rotor gas turbine (SRGT), uses a single rotating assembly incorporating a central hub, a supersonic turbine rotor, a supersonic compressor rotor, and a rim-rotor. This SRGT architecture can potentially increase engine power density while significantly reducing manufacturing costs. The paper presents the preliminary design of a 5 kW SRGT prototype having an external diameter of 72.5 mm and rotational speed of 125,000 rpm. The proposed aerodynamic design comprises a single stage supersonic axial compressor, with a normal shock in the stator, and a supersonic impulse turbine. A pressure ratio of 2.75 with a mass flow rate of 130 g/s is predicted using a 1D aerodynamic model in steady state. The proposed combustion chamber uses an annular reverse-flow configuration, using hydrogen as fuel. The analytical design of the combustion chamber is based on a 0D model with three zones (primary, secondary, and dilution), and computational fluid dynamics (CFD) simulations are used to validate the analytical model. The proposed structural design incorporates a unidirectional carbon-fiber-reinforced polymer rim-rotor, and titanium alloy is used for the other rotating components. An analytical structural model and numerical validation predict structural integrity of the engine at steady-state operation up to 1000 K for the turbine blades. Experimentation has resulted in the overall engine performance evaluation. Experimentation also demonstrated a stable hydrogen flame in the combustion chamber and structural integrity of the engine for at least 30 s of steady-state operation at 1000 K.

Numerical Study of the Shock Wave Propagation in a Micron‐Scale Contracting Channel

Entry of a shock wave into a microchannel and its propagation in the channel are studied numerically by the continuum and kinetic approaches. It is shown that the shock wave is amplified immediately after it enters the microchannel. After that, the shock wave in an inviscid computation propagates over the microchannel with a constant velocity. In a viscous computation, the shock wave velocity decreases and the wave attenuates. Qualitative agreement between experimental data and viscous computations is demonstrated.

Spherical Indentation Testing on Ballistic Gelatin and Perma-Gel

This paper reports on a series of indentation tests performed on ballistic gelatin (10%) and Perma-Gel. In these experiments, both gels were submitted to strain rates varying from 0.1 and 2.7 s−1 in quasi-static indentation. Two methods were used to evaluate the Young’s modulus from quasi-static indentation test: the Hertz theory and the Oliver-Pharr model. The dependence of strain rate was also analyzed. Finally, dynamic indentation tests were performed on both gels at frequencies of 0.1 and 1.0 Hz to evaluate the gel’s viscoelastic properties characterized by the storage modulus, the loss modulus and the phase angle.Copyright

High-g Field Combustor of a Rim–Rotor Rotary Ramjet Engine

High-g field combustion, such as in rotary ramjet engines, is a promising approach to reduce nitride oxides and combustor size by taking advantage of the flame acceleration due to the buoyancy of the products over the reactants. This paper presents a high-g field combustor design for a rim–rotor rotary ramjet engine. In this device, a premixed flow of air and fuel is ignited in the nonrotating inlet track and then swallowed and stabilized in the rotating combustion chamber. Outboard ignition frees the rotating structure from igniters, increasing the maximal tangential speed of the engine and thus its maximal efficiency. The rotating combustor design benefits from extreme centrifugal fields (105g to 107g) for both stabilizing the flame during ignition and maximize flame velocity. A simple buoyancy-driven combustion model allows estimating the combustor length and shows good agreement with numerical simulations, which demonstrate a combustion efficiency to be higher than 85%, even with some reactants bypass...

Improving the sound absorbing efficiency of closed-cell foams using shock waves

Producing closed-cell foams is generally cheaper and simpler than open-cell foams. However, the acoustic efficiency of closed-cell foam materials is poor because it is very difficult for the acoustic waves to penetrate the material. A method to remove the membranes closing the cell pores (known as reticulations) and thus to improve the acoustic behavior of closed-cell foam material is presented. The method is based on the propagation of shock waves inside the foam aggregate where both the shock wave generator and the foam are in air at room conditions. Various shock treatments have been carried out on a Polyurethane foams and the following conclusions were drawn: (1) the reticulation rate increases and thus the airflow resistivity decreases while increasing the amplitude of the shock treatment; (2) the softness of the foam increases; (3) the process is reliable and repeatable and (4) the obtained acoustic performance is comparable to classical thermal reticulation.

Shock Wave Generation through Constructive Wave Amplification

As new biomedical and industrial applications of shock waves emerge, the need to accurately and economically generate shocks is becoming more critical. Since a very large potential resides in biology and medicine areas for diagnostic and therapeutic uses, shock waves need to be efficiently produced in cells, tissues and organs. In the past, there have been a number of methods used to produce shock waves in liquids, all characterized by a large and rapid energy deposition, either through the detonation of an explosive, the irradiation of a target with a pulse of laser energy, the dumping of electricity through a spark gap, or the sudden acceleration of a piston, either by electromagnetic or piezoelectric means. There are well known shortcomings associated with each of these methods, such as the requirement for high-voltage electronics, the manipulation of explosives and/or the lack of control over the shock properties [1]. This paper presents a new method to generate highamplitude pressure pulses in liquids exploiting the advantages of low amplitude piezoelectric generators.

THROUGH SILICON VIAS INTEGRABLE WITH THIN-FILM PIEZOELECTRIC STRUCTURES

This paper reports on the design and microfabrication of novel through silicon vias (TSV) that are compatible with high-temperature processing of piezoelectric structures. The present approach uses metal deposition in cavities etched in the SOI handle layer of the wafer and electrically isolated islands in the device layer. This design avoids the shortcomings of previous TSV designs, which either introduce large topologies on the wafer surface, include metals that cannot sustain high-temperature processing or use poor electrical insulators. TSVs microfabricated using this new approach exhibit good performance, specifically small resistance between the front and backside metal pads, isolation from the ground plane and small capacitance between the vias and the ground. These TSVs are eminently suitable for devices requiring high-temperature processing, such as thin-film piezoelectric sensors and actuators.

Comparison of methods for generating shock waves in liquids

We present two methods for producing high-amplitude pressure pulses in liquids. The electromagnetic generator, commonly used in lithotripters, is difficult to reduce in size, lacks complete control over the pressure pulse and requires high-voltage electronics. On the other hand, a time-reversal method is used to generate high-power acoustic pulses with a low-power electronic piezoeletric transducer.