Разработка джозефсоновского параметрического усилителя бегущей волны нa основе алюминиевых СИС-переходов

We designed, fabricated, and tested several prototypes of a Josephson Travelling Wave Parametric Amplifier (JTWPA) with aluminum SIS junctions integrated in series array of dc SQUIDs in the central line of coplanar waveguide. Three types of fabrication recipes were tested: two with shadow evaporation and one with magnetron sputtering and direct e-beam lithography. IV curves of SQUIDs were measured at bath temperature of 0.3 K. We developed a cryogenic setup for meas-urements of spectral characteristics of JTWPA comprising cold HEMT amplifier with circulator, cold attenuators and filters in signal and pump coaxial lines. Resonant characteristic of coplanar quarter-wave resonator with directional coupler intended for short JTWPA was measured.

Variable intake manifold geometry influence on volumetric efficiency enhancement at gaseous engine starting speeds

This paper studied the effect of variable intake length manifold on filling and volumetric efficiency at starting engine speeds using numerical and experimental process. The investigation is based on acoustic supercharging phenomenon. For this purpose, 1-D engine gas-flow model was developed and optimum intake lengths for several low engine speeds were determined using acoustic theory based-resolution. Using the method of characteristics, pressure waves were predicted at the end of intake line length (intake valve level) in order to test the dynamic inertial supercharging phenomena. The quarter-wave resonator technique was taken into consideration to explore the inlet pressure pulsations. Simulations of pressure wave propagation were achieved during intake stroke and intake valve closed phase. Simulation predictions confirmed the analytically calculated optimum intake length. Numerical investigations were carried out on five in-cylinder flow moving through intake system; air, air-gasoline, air-LPG, air-H2 and air-LPG-H2 blend. The percentages of supplied hydrogen with LPG were 0%, 5%, 10%, 15% and 20% in volume. To experimentally validate the analytical founded lengths, an instrumented cold-flow four cylinder Ford SI engine test bench was prepared. Flow through variable intake length manifold was analyzed. Geometry variation was performed on the plenum length. Three engine low speeds are tested; 500 rpm, 750 rpm and 1000 rpm. The experiment results showed an in-cylinder velocity increase by about 60%, 58% and 48% using the optimal intake length at 500 rpm, 750 rpm and 1000 rpm respectively. Furthermore, the collected data proves that varying intake pipe length continuously with the engine speed leads to an average of 39.7% improvement in volumetric efficiency from the original engine configuration at 1000 rpm.

Heat Transfer in Pulsating Flow and Its Impact on Temperature Distribution and Damping Performance of Acoustic Resonators

A numerical framework for the prediction of acoustic damping characteristics is developed and applied to a quarter-wave resonator with non-uniform temperature. The results demonstrate a significant impact of the temperature profile on the damping characteristics and hence the necessity of accurate modeling of heat transfer in oscillating flow. Large Eddy Simulations are applied to demonstrate and quantify enhancement in heat transfer induced by pulsations. The study covers wall-normal heat transfer in pulsating flow as well as longitudinal convective effects in oscillating flow. A discussion of hydrodynamic and thermal boundary layers provides insight into the flow physics of oscillatory convective heat transfer.

Self-oscillatory flow in the Hartmann resonator – Numerical simulation

Self-oscillatory flow in the Hartmann resonator is numerically calculated within the framework of ideal (inviscid and non-heat-conducting) gasdynamics. The calculations are performed for the case of a sonic jet impinging on a tube varying from that with a sealed inlet (rod) to a fairly deep cavity. The spacing between the tube and the nozzle and the nozzle pressure ratio are also varied in the calculations. On the basis of the calculated results the oscillation process is described in detail and its mechanism is revealed for both shallow and deep tubes. For shallow tubes and a rod it is due to an imbalance in the flow rate and momentum between two regions in the jet that impinges on the obstacle. For deep tubes the oscillations are due to the tube filling and evacuation somewhat reminiscent of the process occurring in a one-quarter-wave resonator. In any case no signature of a feedback loop in the external acoustic field of the jet was detected. The results of the calculations are in good agreement with experimental data. The effects of mounting a lip on the tube (transition from a low- to high-frequency operation mode) and heating in the Hartmann tube are also discussed.