Plasma assisted combustion: Dynamics and chemistry

http://engine.princeton.edu/Publications/Ombrello_2010-2.pdf

Flame propagation enhancement by plasma excitation of oxygen. Part I: Effects of O3

conferencia sobre "Particle Image Velocimetry" de les 13:00-14:00 a la Sala de Juntes de l'FNB impartida pel professor Peter Bueken da l'Antwerp Maritime Acedemy (Belgica)

Particle Image Velocimetry

A review of livestock monitoring and the need for integrated systems

This paper presents a method aimed at recognizing environmental sounds for surveillance and security applications. We propose to apply one-class support vector machines (1-SVMs) together with a sophisticated dissimilarity measure in order to address audio classification, and more specifically, sound recognition. We illustrate the performance of this method on an audio database, which consists of 1015 sounds belonging to nine classes. The database used presents high intraclass diversity in temps of signal properties and some kind of interclass similarities. A large discrepancy in the number of items in each class implies nonuniform probability of sound appearances. The method proceeds as follows: first, the use of a set of state-of-the-art audio features is studied. Then, we introduce a set of novel features obtained by combining elementary features. Experiments conducted on a nine-class classification problem show the superiority of this novel sound recognition method. The best recognition accuracy (96.89%) is obtained when combining wavelet-based features, MFCCs, and individual temporal and frequency features. Our 1-SVM-based multiclass classification approach overperforms the conventional hidden Markov model-based system in the experiments conducted, the improvement in the error rate can reach 50%. Besides, we provide empirical results showing that the single-class SVM outperforms a combination of binary SVMs. Additional experiments demonstrate our method is robust to environmental noise.

Using One-Class SVMs and Wavelets for Audio Surveillance

There has been a need for improved flow prediction methods for low pressure turbine (LPT) blades operating at high altitudes with a reduced inlet Reynolds number. These conditions present an increased amount of laminar-to-turbulent transitional flow within the boundary layers on the LPT blade surfaces. Also, boundary layer separation is more likely to occur within the flowfield of the LPT stages due to the lower freestream velocities in the regions of adverse pressure gradients on the suction surfaces. More accurate predictions of aerodynamic losses due to low Reynolds effects are needed for CFD to provide more accurate input to the design process for LPT stages operating at high altitudes. Steady flow CFD simulations of flow in a multistage LPT geometry were completed at nominal and high altitude conditions with the conventional Spalart-Allmaras turbulence model and a recentlydeveloped three-equation eddy-viscosity type transitional flow model. These models were used in combination with a mixing plane model for the simulation of flow through a three stage low pressure turbine. Flow visualizations were completed using surface flow and streamline calculations to help identify vortical structures present within the flowfield. Also, the total pressure loss coefficient was calculated for each blade row. Qualitative comparisons indicate the amount and the location of the flow separation differed significantly depending on the chosen turbulence model. Overall, the high altitude condition had an increased amount of separated flow compared to the nominal altitude condition resulting in an increase in the loss coefficient. The altitude effect on the laminar-to-turbulent transition location was studied using the three-equation model. The model provided a more detailed understanding of the aerodynamic loss mechanisms present in low Reynolds number flows, since it accounted for transitional boundary layer flow effects. Based on the these results, the CFD using the three-equation model has the potential to be a more effective method for turbine flow prediction at low Reynolds numbers compared to conventional RANS turbulence models.

Turbulence Model Comparisons for Mixing Plane Simulations of a Multistage Low Pressure Turbine Operating at Low Reynolds Numbers

Hot-Flow Testing of an Integrated Aero-Ramp-Injector/ Plasma-Igniter for Scramjets with Hydrocarbon Fuel

A potential flow computer model that can handle blade row interaction problems has been used to analyze the circumferential static pressure distribution at the trailing edge plane of the last rotor in an axial compressor which is produced by a downstream stator/strut system. The computer model is based on the DouglasNeumann formulation. The code was used to design a circumferentially nonuniform stagger angle distribution for the stator that reduced the static pressure disturbance on the rotor. The predicted circumferential static pressure distribution and its resulting frequency content at the rotor trailing edge station for the baseline (uniform circumferential stagger angles) stator and for the optimized stator are compared to static pressure data and derived frequency content from engine tests of each configuration. The results show good agreement between the model predictions and the test data, The results are further confirmed by measurements of rotor strain levels with the baseline stator and with the optimized stator, which show a proportional decrease in rotor strain for the optimized stator configuration. Since incorporation of this low-cost modification, there has been no evidence of vibratory induced rotor distress, thereby improving engine reliability and maintainability and enhancing customer satisfaction.

/pdf/the-use-of-circumferentially-nonuniform-stators-to-attenuate-354n1kwc76.pdf

The Use of Circumferentially Nonuniform Stators to Attenuate LP Compressor Rotor-Stator-Strut Aerodynamic and Mechanical Interactions

This study was conducted for the purpose of providing a more fundamental understanding of separated flow in cascades and to provide performance data for fully-stalled blade rows. Cascades of a single blade geometry and a solidity of unity were studied for three stagger angles and the full range of angle of attack, extending well into the stalled flow regime. Results are presented from flow visualization and time-mean velocity measurements of stalled flow in the cascade. Surface and smoke flow visualization revealed that the blade stagger angle is a key parameter in determining the location of the separation line and the occurrence of propagating stall. Time-mean velocity measurements obtained with a dual hot split-film probe also showed that the separated velocity profiles within the blade passages and the profiles in the wake have distinctly different characteristics depending on the stagger angle.Copyright © 1992 by ASME

/pdf/separated-flow-in-a-low-speed-two-dimensional-cascade-part-i-rp5f71x7pq.pdf

Separated Flow in a Low Speed Two-Dimensional Cascade: Part I — Flow Visualization and Time-Mean Velocity Measurements

Turbofan engine performance depends highly on the characteristics and conditions of the inlet flow. Swirl distortions, caused by non-uniformities in flows arising from boundary layer or ground/fuselage vortex ingestion are of concern and need to be fully understood to guarantee efficiency and safety of propulsion systems. To investigate a fundamental single-vortex distortion development in a duct at different Reynolds numbers, a StreamVane distortion generating device was designed and experimentally analyzed in a small-scale low-speed wind tunnel (ReD 500,000) and in a full-scale engine testing rig (ReD 3 million). Stereoscopic particle image velocimetry was used to measure the three-component velocity fields at discrete measurement planes downstream of the distortion device. Results show that the secondary flow is generated and develops very similarly in both scales, and is mostly driven by two-dimensional (2D) vortex dynamics. Induced velocities arising from the proximity of the vortex to the duct wall causes the vortex center to convect circumferentially around the duct, in the same sense as the vortex rotation, as it travels downstream. Small-scale turbulence results show small-scale instabilities related to the development of the vortex. This work shows that the development of this vane-generated, vortex-dominated flow is largely Reynolds number independent for the covered range, so that details of similar duct-bounded flows can be analyzed in depth in small-scale experiments, decreasing development efforts and cost.

Walter F. O'Brien

Papers

Turbulence Model Comparisons for Mixing Plane Simulations of a Multistage Low Pressure Turbine Operating at Low Reynolds Numbers

Hot-Flow Testing of an Integrated Aero-Ramp-Injector/ Plasma-Igniter for Scramjets with Hydrocarbon Fuel

The Use of Circumferentially Nonuniform Stators to Attenuate LP Compressor Rotor-Stator-Strut Aerodynamic and Mechanical Interactions

Separated Flow in a Low Speed Two-Dimensional Cascade: Part I — Flow Visualization and Time-Mean Velocity Measurements

Vortical Flow Development in Round Ducts Across Scales for Engine Inlet Applications