Micro-Jet Test Facility for Aerospace Propulsion Engineering Education

This paper describes the methodology that has been developed and implemented at the School ofAeronautics (ETSIA) of the Universidad Politecnica de Madrid (UPM) to familiarize aerospaceengineering students with the operation of real complex jet engine systems. This methodology has atwo-pronged approach: students carry out preparatory work by using, first, a gas turbineperformance prediction numerical code; then they validate their assumptions and results on anexperimental test rig. When looking at the educational aspects, we have taken care that, apart frombeing sufficiently robust and flexible, the experimental set-up is similar to real jet engine rigs, so thestudents are not constrained to exploring a much too limited parametric space. Also, because afacility like this is usually subject to extensive and somewhat rugged use, we have focused on a lowcost design

Interacción de un pulso de láser de alta potencia con una microesfera sobredensa

El problema fundamental en la obtención de energía de fusión controlada es el confinamiento de un plasma durante el tiempo necesario para producir reacciones termonucleares que liberen, al menos, la energía consumida en la producción de dicho plasma. Numerosos estudios han mostrado, por una parte, la posibilidad de conseguir el confinamiento del plasma mediante la acción del láser y, por otra, la importancia que la interacción laser-plasma tiene en la consecución de reacciones termonucleares controladas mediante la acción del láser. Por esta razón, los esfuerzos encaminados al conocimiento de la interacción de la luz de láser con la materia se han visto enormemente incrementados en los últimos años. En este trabajo se han analizado algunos aspectos fundamentales de la interacción laser-plasma. En particular, y para el régimen de onda térmica (que corresponde a pulsos de láser de muy alta intensidad y duración extraordinariamente corta), se ha obtenido un método integral para el cálculo de la evolución espacio temporal de la onda térmica esférica; la comparación de resultados obtenidos de la aplicación del método integral con resultados numéricos, muestra un acuerdo excelente. Se ha analizado, también dentro de este régimen, la expansión del plasma al vacío; los resultados obtenidos, cuando se ignoran los efectos de la presión de radiación, muestran la existencia de tres tipos diferentes de solución, según que la temperatura aumente, permanezca constante, o disminuya con el tiempo (dT/dt menor, igual, o mayor que cero). Posteriormente, se ha extendido el análisis incluyendo el efecto de la presión de radiación de la onda de luz incidente; en particular, se ha encontrado que existe siempre un frente de rarefacción (onda de choque de rarefacción), que engloba a la superficie crítica (superficie en que la densidad electrónica N coincide con la densidad crítica), y modifica la región supercrítica (Ñ mayor que Nc) dando lugar a cavidades, zonas de densidad constante ("plateaus"), u ondas de choque, según que dT/dt menor, igual o mayor que 0. La región subcrítica (ñ menor que Nc) ha sido también analizada empleando un método de escalas múltiples. Finalmente, se ha estudiado el efecto que la presión de radiación ejerce sobre las especies iónicas de diferente relación masa carga (A/Z); en el caso de dos especies iónicas, se ha encontrado que la especie de menor A/Z experimenta, respecto a la otra especie, una gran aceleración en una zona, que engloba la superficie crítica, y cuyo espesor es del orden de la longitud de onda de la luz del láse

Self-consistent profile modification in the underdense region of laser-produced plasmas

Profile modification in the underdense region of laser-plasmas with spatially uniform temperature Te, is studied. A multiple scale method is used to describe self-consistently the plasma flow and the wave field, in (i) the scale of the field wavelength, and (ii) the overall expansion scale. For Te taordinary differential equations with definite boundary conditions are obtained. For a = 0 and weak fields, we explicitly solve the equations and relate the field in the critical layer to the incident field

Comment on "Steady-state planar ablative flow"

In a recent paper Manheimer et al.1 attempted to proceed beyond older analyses2 on the ablative corona ejected by planar láser targets. Here we comment on some aspects of the analysis of Ref. 1, common to most previous papers on the subject

A novel particle tracking and break-up detection algorithm: application to the turbulent break-up of bubbles

A new method has been developed to measure experimentally the break-up properties of bubbles. The technique is based on the application of a particle tracking velocimetry algorithm to high-speed video images not only to measure the velocity of the bubbles, but also to detect the break-up events. Thus the algorithm is able to associate every broken bubble with the daughter bubbles formed upon their corresponding break-up. Moreover, the lifetime, as well as the number and size of fragments resulting from the break-up process, can be measured for a large number of bubbles. Statistical processing of the information collected allows us to compute the break-up frequency and daughter size distribution of the bubbles as a function of the bubble size and the mean properties of the base flow. The method has been employed to study the break-up of a cloud of bubbles injected at the central axis of a turbulent water jet. Experimental results for the break-up frequency and daughter bubble size distribution are also presented to illustrate the performance of the technique

On the breakup of an air bubble injected into a fully developed turbulent flow. Part 2. Size PDF of the resulting daughter bubbles

Based on energy principles, we propose a statistical model to describe the bubble size probability density function of the daughter bubbles resulting from the shattering of a mother bubble of size D0 immersed in a fully developed turbulent water flow. The model shows that the bubble size p.d.f. depends not only on D0, but also on the value of the dissipation rate of turbulent kinetic energy of the underlying turbulence of the water, [epsilon]. The phenomenological model is simple, yet it predicts detailed experimental measurements of the transient bubble size p.d.f.s performed over a range of bubble sizes and dissipation rates [epsilon] in a very consistent manner. The agreement between the model and the experiments is particularly good for low and moderate bubble turbulent Weber numbers, Wet = [rho][Delta]u2(D0)D0/[sigma] where the assumption of the binary breakup is shown to be consistent with the experimental observations. At larger values of Wet, it was found that the most probable number of daughter bubbles increases and the assumption of tertiary breakup is shown to lead to a better fit of the experimental measurements

On the breakup of an air bubble injected into a fully developed turbulent flow. Part 1. Breakup frequency

The transient evolution of the bubble-size probability density functions resulting from the breakup of an air bubble injected into a fully developed turbulent water ow has been measured experimentally using phase Doppler particle sizing (PDPA) and image processing techniques. These measurements were used to determine the breakup frequency of the bubbles as a function of their size and of the critical diameter Dc defined as Dc = 1.26 ([sigma]/[rho])3/5[epsilon][minus sign]2/5, where [epsilon] is the rate of dissipation per unit mass and per unit time of the underlying turbulence. A phenomenological model is proposed showing the existence of two distinct bubble size regimes. For bubbles of sizes comparable to Dc, the breakup frequency is shown to increase as ([sigma]/[rho])[minus sign]2/5[epsilon][minus sign]3/5 [surd radical]D/Dc[minus sign]1, while for large bubbles whose sizes are greater than 1.63Dc, it decreases with the bubble size as [epsilon]1/3D[minus sign]2/3. The model is shown to be in good agreement with measurements performed over a wide range of bubble sizes and turbulence intensitie

Two-temperature model of the coronal irradiated pellets

A two electron-temperature, quasi-steady model of the corona of a laser-ablated pellet is considered. Ablation pressure, critical radius and mass flow rate are determined. Results are close to those obtained with heat flux saturation well below the free-streaming limit