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

Assessment of experimental optical techniques for characterizing heat transfer using numerical simulations

This manuscript addresses the application of numerical simulations for assessing the error in the measurement of the bulk temperature along the laser beam of a 3D flow using a 2D Moiré deflectometry analysis. To analyze the effect of different flow parameters on the error, a 3D computational model of an experimental system was developed. The simulated domain represents the well-known solution of the backward facing step in a rectangular channel but includes a hot-plate at the bottom of the step to enhance the heat transfer effects. The geometry resembles that found in a general heat exchanger. The difference between the computed bulk temperature of the flow and the average temperature obtained via the 2D Moiré is analytically evaluated for various assumed general temperature profiles; the numerically computed profiles of temperature indicates that the error decreases with the channel aspect ratio. The use of CFD enables the determination of the flow topology and thus an evaluation of the 3D flow behavior that will cause the measurement error. A parametric study was performed for different flow conditions, namely, the aspect ratio of the channel, the inflow conditions (flow velocity or Reynolds number), and the temperature of the hot wall. The results indicate that the Moiré technique is suitable for evaluating the bulk temperature in typical heat exchange devices and flow conditions

A study of the combustion problems of solid materials at conditions existing in space stations

Combustión of a solid at microgravity conditions at zero or at very small forced flow velocities is in the first place discussed, pointing out that this is the basic process of a fire in a manned spacecraft, in which might exist small air currents originated by the air conditioning equipment or by the motion of the people. Results of an experimental programme carried out in the 23rd ESA Flight campaign 96/12 and utilising a NASA aircraft laboratory, are shown and discussed. Six combustión chambers were utilised provided with video and infrared cameras. Non visible flames in the visual range were originated at two oxygen concentrations, and photographs were taken by means of an infrared camera. Several ignition tests at different oxygen concentrations were performed and flammability limits were obtained. Fíame spread velocities were measured and compared at three different gravity levéis (1 g, ~10"2 g and 10"4 g). A combustión research programme to be carried out in a Texus rocket, already in progress is briefly discussed. Finally, the scope of a complete research programme, which is in the process of being carried out in the NASA combustión module of the International Space Station is briefly resumed

An experimental research programme on heterogeneous combustion processes under microgravity conditions. Preliminary results

In the present work preliminary results are given of an experimental programme on flame spreading over the surface of PMMA rods in NgO2 mixtures under microgravity conditions. Results were obtained in the NASA KC-135 aircraft laboratory. Six experiments were carried out in March of this year and 36 more experiments will be conducted in March 1987. These preliminary experiments allowed to determine the flame spreading velocities for three different mixture compositions, showing that they were smaller but of the same order of magnitude than downwards spreading velocities at one g and for the same mixture condition

An Experimental Programme on Flame Spreading at Reduced Gravity Conditions.

An experimental programme on flame spreading over the surface of polymethylmetacrylate (PMMA) samples has been conducted at reduced gravity conditions in the NASA KC-135 air craft laboratory. A total of 36 experiments were performed. From the results of these experiments the flame spreading velocities over PMMA samples have been obtained, as well as their laws of variation with pressure and mixture composition. Both cylindrical and flat samples have been investigated. These results were compared with those obtained for the same conditions of pressure and composition on the ground at 1 g. In this way it was shown how gravity does influence the spreading process and how this influence was affected by pressure and mixture composition

Analytical Calculation of Stall-inception and Surge Points for an Axial-flow Compresor Rotor

Recently, a theoretical criterion to calculate the stability of an axial-flow compressor rotor has been presented in the scientific literature. This theoretical criterion was used for determining the locus of the stability line over the rotor map and for predicting the post-stall evolution of the constant-speed line of a rotor. The main objective of this paper is to improve the predictions of such a model. To do that, the paper proposes a different characterization of the characteristic azimuthal length and a calculation of the ratio of specific heats based on a polytropic exponent. Thanks to these new values, the model predicts two bifurcation points in the behaviour of the flow: the inception point of the instability and the surge point. Experimental data from a pure axial compressor are used to validate the model showing that the prediction of the flow coefficient at the surge point has an error inferior to 5%. For the rotor studied, the paper provides a quantitative and qualitative description of the inception of the instability and of the mechanism involved in the instable region of the compressor map. The paper also discusses the role of rotor efficiency in the position of the bifurcations and gives a sensitivity analysis of its position. Finally, it presents a discussion about how the model can explain the different behaviours exhibited by the same rotor when the flow coefficient is reduce

Moiré-Fourier deflectometry for local heat transfer measurement over a backward-facing step

This paper explores the possibility of using the Moire-Fourier deflectometry for measuring the local heat transfer coefficient inside small confined flows (micro-channels) and their relevance for checking theoretical models. This optical technique, supplemented with a digital image processing method of fringes, is applied for studying the local heat transfer over a backward facing step. The experimental results are compared with numerical results obtained from a commercial code, which has been contrasted with relevant solutions from the literature and bulk fluid temperature measurements at the inlet and outlet sections. In order to show the possibilities of the experimental technique, the influence of assuming an adiabatic wall on the numerical heat-transfer model is examined and the degree of agreement is discussed. As a result, the paper shows that the proposed Moiré-Fourier technique is a simple experimental setup suitable for temperature measurements with an accuracy similar to the thermocouples but with a spatial resolution near 0.01 mm.Moiré-Fourier deflectometry for local heat transfer measurement over a backward-facing ste

Programas de investigación sobre propagación de llamas en condiciones de gravedad reducida

Se presenta en este trabajo un resumen del programa experimental sobre propagación de llamas a gravedad reducida que se está llevando a cabo por la Escuela Técnica Superior de Ingenieros Aeronáuticos; programa en el que últimamente colabora la empresa SENER. La propagación de llamas sobre la superficie de un sólido en atmósfera reactante es un tipo de proceso fuertemente afectado por la convección libre, y por tanto, especialmente sensible al valor de la gravedad

Heterogeneous combustion processes under microgravity conditions

An experimental programme on flame spreading over the surface of PMMA (plexiglass) samples has been conducted under microgravity conditions in the NASA KC-135 aircraft laboratory. A few experiments (three) were conducted in 1986 under the preceding contract no. 6284/85/F/FL, but the largest part of the experimental programme has been carried out under the present contract in two parabolic flights campaigns. A total of 36 experiments were performed, most of them successful. From the results of these experiments the flame-spreading velocities over PMMA samples have been obtained, as well as their laws of variation with pressure and mixture composition. Both cylindrical (axial symmetry) and flat (bidimensional symmetry) samples have been investigated

Study on combustion processes in reduced gravity : final report volume I

1. ABSTRACT OF THE WORK 1.1. GENERAL CONSIDERATION ON THE WORKING PACKAGES The following tasks have been carried out under the present Contract: WP1. Continuation of the experiments on flame spreading in parabolic aircraft flights, conducted in one flight campaign. These experiments have been, in part, a continuation of the preceeding research programmes and they were directed to the study of the influence of fuel thickness at reduced gravity on the flame spread velocity. In addition, a few experiments were carried out in order to obtain some preliminary information on possible combustion experiments to be performed in a sounding rocket module. WP2 and WP3. These works on the sounding rocket module and on the sounding rocket experiments were preceeded by a common study, which consisted in a review of the combustion experiments that could be carried out in a sounding rocket module. The requirements of the experiments were analised, with special emphasis on the essential factors of the time and space needed for each possible experiment. It was definitively concluded that there is no practical way to keep constant the gaseous atmospheric composition in the module chamber throughout a stationary combustion process in a still atmosphere. This is due to the fact that there is not any practical feasible way to extract the combustion products and to feed into the module the oxygen or the reactant gases consumed without strongly disturbing the flow field. This occurs because under microgravity conditions gas velocities in combustion processes at constant pressure are essentially controlled by diffusion and they are usually very small. 3. As a consequence, the module has to contain a sufficient amount of oxidizer such that its variation during the combustion process should be permissible. This requirement imposes limitations in the volume and combustion time, which are interdependent and in the size of the experiment. In addition, the volume available has to be sufficiently large in order to avoid significant interference of the walls of the module on the combustion field. If the experiment is of a non-stationary nature and the flame size increases with time, as it occurs in many combustion processes, this imposes another limitation in the combustion time and in the size of the experiment. The aforementioned review of the combustion processes is shown in this Final Report and from its conclusions the basic data for the study and specifications of the combustion module were obtained. 1.2. MULTIPLE EXPERIMENTS From the aforementioned review it was concluded than in most combustion experiments times of the order of one minute would be sufficient. Since there are six minutes at reduced gravity available, the problem of utilizing the module for several experiments has to be considered, specially taking into account the high cost of the launching of a sounding rockets. Except for the experiments in which a little amount of oxidizer is consumed, such as in droplet combustion, reutilization of the module for multiple experiments require emptying the module and refilling it with the specified gaseous mixture. This process is mechanically simple but it presents the difficult problem of knowing the time required for the oxygen or gaseous mixture introduced into the chamber to become at rest. The process is asymptotic, therefore it has to be specified the minimum value admitted for the gas fluctuation velocities (for example <2 mm/s). The analytical solution of this problem is very difficult, and it is presently being studied by NASA. Considering its importance, the problem has been studied experimentally under the present Contract. It has been concluded after a series of experiments with different tracers, that after elapsing times of the order of two minutes the fluctuation velocities were lower than 2 mm/s, which were considered sufficiently small. This implies that two or three refills are possible in each flight. A large amount of experiments would occupy the full available diameter of the module [-40 cm). Some experiments would need smaller diameters. This opens the possibility of utilizing several chambers inside the module, increasing the possibility of multiple experiments for each flight and reducing costs, and avoiding refilling in some cases. A preliminary desing of this multiple combustion chamber solution has been carried out. 1.3. FORCED CONVECTION EFFECTS AT LOW REYNOLDS NUMBER Forced Convection effects are currently considered of high interest in combustion processes at reduced gravity. This is due to two reasons: in the first place, forced convection effects at low Reynolds numbers cannot be experimentally studied at one g on the ground, because they are masked by free convection effects. On the other hand, if a fire takes place in a spacecraft or space laboratory it will be most likely take place in an environment of low velocity gas currents originated by the air conditioning equipment or even by the motion of people. Forced convection effects can be studied in the sounding rocket module in two different ways: by moving the burning smaple along the module keeping the oxygen or oxidizers at rest, or by keeping the sample at rest and producing a continuous flow of gas at a given velocity. Although their study was not specified in this Contract, both systems have been analysed. The first system is relatively simple, requiring refilling of the module. Three or four experiments would be possible to carry out in each flight. The second systems is mechanically very complicated requiring two valves controlled probably by a microcomputer. A specific system is proposed and studied. Its principal controlling laws are discussed, as well as the main problems and possible solutions. In principle, this system offers the possibility of carrying out more experiments per flight than the first system. However, some important transient problems have to be thoroughly studied, requiring a test programme before concluding that the proposed system is a viable or better solution. 1.4. WP4. THEORETICAL STUDIES The theoretical studied have been devoted to quiescent combustion and flame spreading utilizing numerical methods and an order of magnitude analysis. Several important results have been obtained, as for example the influence of gravity on flame spreading depending on the fuel thickness, which have been experimentally verified during the parabolic flights. In addition a study on the influence of forced convection on the flame spreading process has been carried out