Generation of combustion noise is here studied in a realistic turbine stage configuration, where the temperature fluctuations generated by an aeronautical burner (responsible of the direct combustion noise generation, often neglected in most of the studies) are modelled using a cylindrical fluctuating energy source term placed upstream of the inlet guide vanes. This modelling not only better accounts for the actual physical combustion noise generation phenomena, but also for the actual stratification of temperature at the combustor exit and covers a broader range of exciting frequencies as in actual engines. The temperature fluctuations generated by this realistic fluctuating energy source term are then convected through the turbine stage and the resulting noise is analyzed and compared with previous LES results with ideal monochromatic entropy forcing and analytical compact methods. New physical insight on the various noise generation mechanisms and mode conversion is also provided.
spots and vorticity through the turbine blades generates acoustic waves. The propagation of acoustic waves was first studied by Tsien [1] in a rocket engine within the combustion instability framework. Marble and Candel [2] extended this study to take into account entropy waves and computed the wave transfer functions of a compact nozzle (where the nozzle length is considered small compared with the wavelength of the perturbations). Cumpsty and Marble [3] extended the 1D compact nozzle theory of Marble and Candel to take into account 2D compact stator and rotor blades. Huet and Giauque [4] developed a model to take into account the non linear effects produced by high temperature fluctuations (typically above 10% of the averaged background temperature) within the compact theory. Nevertheless, work done by Marble and Candel [2] and Moase et al. [5] showed that the modulus of the transfer functions of chocked nozzles changes significantly with frequency and hence the compact theory is no longer valid. Marble and Candel [2] assume that the nozzle has a defined geometry with a linear velocity profile, obtaining for this very specific case an analytical solution in the form of an hyper-geometric differential equation. Moase et al. [5] considered a chocked nozzle where the velocity profile was approached as piecewise-linear and used the solution of Marble and Candel for each interval to obtain the nozzle transfer functions. Stow et al. [6] used an asymptotic analysis to compute a first order correction to the compact hypothesis in the case of a choked nozzle obtaining an effective nozzle length to correct the phase prediction of the reflection coefficient. Goh and Morgans [7] extended this approach to compute the transition coefficient of a nozzle with a choked flow. Finally, Duran and Moreau [8] solved the quasi 1-D linearised Euler Equations (LEE) giving an extension to the compact assumption to the whole frequency domain for all types of nozzle.
Compact and non-compact analytical solutions of the subsonic operating point of the entropy wave generator experiment are compared with detailed numerical results obtained by large Eddy simulations. Two energy deposition methods are presented to account for the experimental ignition sequence and geometry: a single-block deposition as previously used and a delayed deposition that reproduces the experimental protocle closely. The unknown inlet acoustic reflection coefficient is assumed to be fully reflective to be more physically consistent with the actual experimental setup. The time delay between the activation of the heating modules must be considered to retrieve the temperature signal measured at the vibrometer and pressure signals at the microphones. Moreover, pressure signals extracted from the large Eddy simulations in the outlet duct using the delayed ignition model clearly reproduce the experimental signals better than the analytical models. An additional simulation with actual temperature fluctuations directly injected at the inlet of the computational domain clearly shows that the pressure fluctuations produced by the acceleration of the hot slug yields indirect noise almost entirely. Finally, the entropy spot is shown to be distorted when convecting through the turbulent flow in the entropy wave generator nozzle. Its amplitude decreases and its shape is dispersed, but hardly any dissipation occurs. The distortion appears to be negligible through the nozzle and become important only when convected over a long distance in the downstream duct. As the dominant frequencies of the entropy wave generator entropy forcing are very low, the effects of dispersion by the mean flow are however weak.
Virtual education offers the possibility to implement and put into practice an education process as ample and complex as it is necessary. It keeps us in touch with our students through online resources which turn it into a powerful and attractive way of communication which works based on previously set objectives. In this context the role of the teacher becomes key to achieve a meaningful, effective and quality teaching-learning process. The teacher must possess specific characteristics which will allow him to attain the desired educational objectives. The objective of this research paper is to identify and detail which are the basic competencies that a virtual teacher should cover. In order to carry out this research we made a literature review of texts focused on distance education and teaching skills necessary for it. This activity allowed us to dimension the issues that were of interest and especially to put them in context.
The learning objects and the instructional design have begun to position themselves as important support elements in the teaching of the chair, as well as in the mobility of the students, since through an adequate design it is possible to contribute to a good preparation of the student. which will finally improve the acquisition of a second language by having access to a stay abroad. Objectives, methodology: Identify the importance of the learning object in the design of tools that allow the student to have virtual access while in mobility. An exploratory methodology with questionnaires was applied. Contribution: This document contains the advances of an investigation that is currently being carried out at the Fidel Velázquez Technological University. The purpose of this study is to prove that instructional design is a very important element to support students aspiring to a mobility scholarship or who are already in the process of mobility by contrasting with the opinions of students who have already concluded said process. Although there are advances in the current context in design and the application of instructional design, such a resource has not yet been exploited as such in student mobility and an excellent means should be the application in the classroom from the first courses for the student in the classroom, which will also allow the acquisition of a second language to be successful.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.