The Experts below are selected from a list of 4842 Experts worldwide ranked by ideXlab platform
Ulrich Rist - One of the best experts on this subject based on the ideXlab platform.
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Direct Numerical Simulation of a Square-Notched Trailing Edge for Jet-Noise Reduction
46th AIAA Aerospace Sciences Meeting and Exhibit, 2008Co-Authors: J. Kloker, Ulrich RistAbstract:Sound generation of a subsonic laminar jet has been investigated using direct numerical simulation (DNS). The simulation includes the Nozzle End, modelled by a finite flat splitter plate with Mach numbers of MaI = 0.8 above and MaI = 0.2 below the plate. Behind the Nozzle End, a combination of wake and mixing layer develops. Due to its instability, roll up and pairing of spanwise vortices occur, with the vortex pairing being the major acoustic source. As a first approach for noise reduction, a rectangular notch at the trailing edge is investigated. It generates longitudinal vortices and a spanwise deformation of the flow downstream of the Nozzle End. This leads to a an early breakdown of the large spanwise vortices and accumulations of small-scale structures. The emitted sound is compared with a two-dimensional simulation performed earlier. 2
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Direct Numerical Simulation of a Serrated Nozzle End for Jet-Noise Reduction
High Performance Computing in Science and Engineering `07, 1Co-Authors: Andreas Babucke, Markus J. Kloker, Ulrich RistAbstract:Sound generation of a subsonic laminar jet has been investigated using direct numerical simulation (DNS). The simulation includes the Nozzle End, modelled by a finite flat splitter plate with Mach numbers of MaI = 0.8 above and MaII = 0.2 below the plate. Behind the Nozzle End, a combination of wake and mixing layer develops. Due to its instability, roll up and pairing of spanwise vortices occur, with the vortex pairing being the major acoustic source. As a first approach for noise reduction, a rectangular notch at the trailing edge is investigated. It generates longitudinal vortices and a spanwise deformation of the flow downstream of the Nozzle End. This leads to a an early breakdown of the large spanwise vortices and accumulations of small-scale structures. Compared to a two-dimensional simulation performed earlier [3], the emitted sound is reduced by 6 dB.
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Numerical Investigation of Flow-Induced Noise Generation at the Nozzle End of Jet Engines
Notes on Numerical Fluid Mechanics and Multidisciplinary Design (NNFM), 1Co-Authors: Andreas Babucke, Markus J. Kloker, Ulrich RistAbstract:Sound generation downstream the Nozzle End of a subsonic laminar jet has been investigated using two-dimensional direct numerical simulations (DNS). The Nozzle End is modeled by a finite flat plate with Mach numbers of Ma I = 0.8 above and Ma II = 0.2 below the splitter plate. Behind the Nozzle End, a combination of a wake and mixing layer develops. Due to the high amplification rates, disturbances saturate before a pure mixing layer occurs. Non-linear generation mechanisms produce higher harmonic disturbances in the upper boundary layer, resulting in an only quasi periodic solution. The main acoustic sources correspond to the positions of vortex pairing. Broadband noise is emitted instead of tonal noise, known from the pure mixing layer without a splitter plate [4].
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Mechanisms and Active Control of Jet-Induced Noise
Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 1Co-Authors: Andreas Babucke, Markus J. Kloker, Bruno Spagnoli, Christophe Airiau, Ulrich RistAbstract:Fundamental mechanisms of jet noise are investigated by means of direct numerical simulation. In the mixing layer, subharmonics of the respective vortex pairing are found to be responsible for the main part of the generated noise which is directed in downstream direction. By modifying the phase shift between introduced disturbances it is possible to diminish or enhance relevant portions of the emitted sound. Optimal control has been applied successfully to a plane mixing layer. In the far field, the mean noise level could be reduced. DepEnding on the measurement line, some distributed control or anti-noise is generated by the control. A more realistic configuration is achieved by adding a splitter plate representing the Nozzle End. Rectangular serrations lead to a breakdown of the large coherent spanwise vortical structures and thus provide a noise reduction of 9dB.
C C Yetisen - One of the best experts on this subject based on the ideXlab platform.
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experimental study on ejector refrigeration system powered by low grade heat
Energy Conversion and Management, 2007Co-Authors: Rafet Yapici, C C YetisenAbstract:Abstract An ejector refrigeration system has been designed and constructed to operate with hot water. Such a refrigeration system, designed for low pressure refrigerants, can be operated using energy sources such as solar energy, geothermal energy and waste heat. In this study, the effects of the main operating parameters on system performance were experimentally investigated using R-11 as the working fluid and keeping constant the position of the primary Nozzle End at the inlet plane of the mixing chamber section of the ejector. The experimental study was performed over a range of vapor generator temperatures from about 90 to 102 °C, evaporator temperatures from 0 to 16 °C and condenser pressures from 114 to 143 kPa, and a COP up to 0.25 was obtained. It was seen that if higher cooling capacity and also lower evaporator temperature are desired from the system, the vapor generator temperature should be increased considerably.
Andreas Babucke - One of the best experts on this subject based on the ideXlab platform.
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Direct Numerical Simulation of a Serrated Nozzle End for Jet-Noise Reduction
High Performance Computing in Science and Engineering `07, 1Co-Authors: Andreas Babucke, Markus J. Kloker, Ulrich RistAbstract:Sound generation of a subsonic laminar jet has been investigated using direct numerical simulation (DNS). The simulation includes the Nozzle End, modelled by a finite flat splitter plate with Mach numbers of MaI = 0.8 above and MaII = 0.2 below the plate. Behind the Nozzle End, a combination of wake and mixing layer develops. Due to its instability, roll up and pairing of spanwise vortices occur, with the vortex pairing being the major acoustic source. As a first approach for noise reduction, a rectangular notch at the trailing edge is investigated. It generates longitudinal vortices and a spanwise deformation of the flow downstream of the Nozzle End. This leads to a an early breakdown of the large spanwise vortices and accumulations of small-scale structures. Compared to a two-dimensional simulation performed earlier [3], the emitted sound is reduced by 6 dB.
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Numerical Investigation of Flow-Induced Noise Generation at the Nozzle End of Jet Engines
Notes on Numerical Fluid Mechanics and Multidisciplinary Design (NNFM), 1Co-Authors: Andreas Babucke, Markus J. Kloker, Ulrich RistAbstract:Sound generation downstream the Nozzle End of a subsonic laminar jet has been investigated using two-dimensional direct numerical simulations (DNS). The Nozzle End is modeled by a finite flat plate with Mach numbers of Ma I = 0.8 above and Ma II = 0.2 below the splitter plate. Behind the Nozzle End, a combination of a wake and mixing layer develops. Due to the high amplification rates, disturbances saturate before a pure mixing layer occurs. Non-linear generation mechanisms produce higher harmonic disturbances in the upper boundary layer, resulting in an only quasi periodic solution. The main acoustic sources correspond to the positions of vortex pairing. Broadband noise is emitted instead of tonal noise, known from the pure mixing layer without a splitter plate [4].
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Mechanisms and Active Control of Jet-Induced Noise
Notes on Numerical Fluid Mechanics and Multidisciplinary Design, 1Co-Authors: Andreas Babucke, Markus J. Kloker, Bruno Spagnoli, Christophe Airiau, Ulrich RistAbstract:Fundamental mechanisms of jet noise are investigated by means of direct numerical simulation. In the mixing layer, subharmonics of the respective vortex pairing are found to be responsible for the main part of the generated noise which is directed in downstream direction. By modifying the phase shift between introduced disturbances it is possible to diminish or enhance relevant portions of the emitted sound. Optimal control has been applied successfully to a plane mixing layer. In the far field, the mean noise level could be reduced. DepEnding on the measurement line, some distributed control or anti-noise is generated by the control. A more realistic configuration is achieved by adding a splitter plate representing the Nozzle End. Rectangular serrations lead to a breakdown of the large coherent spanwise vortical structures and thus provide a noise reduction of 9dB.
Shahverdi Kaveh - One of the best experts on this subject based on the ideXlab platform.
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Faraday Waves-and Multiple-Fourier Horns-Based Ultrasonic Nozzles and Nebulizers
eScholarship University of California, 2020Co-Authors: Shahverdi KavehAbstract:Inhalation is an increasingly important route for non-invasive drug delivery for both systemic and local applications. Control of particle droplet size and throughput plays a critical role in the efficient and effective delivery of often expensive medications to the lung. Drugs designed to treat pulmonary diseases or for systemic absorption through the alveolar capillary bed require optimum particle sizes (2 to 6 µm) for effective delivery. Current advanced commercial devices such as Omron and ParieFlow produce droplets or aerosols by a vibrating mesh. All these devices suffer from broad particle size (poly-disperse) distributions and lack of size control capability, and also are plagued by clogging of the mesh orifices used.The new drug delivery device presented in this dissertation has demonstrated capability for control of particle size within the optimum size range at low drive power and desirable throughput and freedom from clogging. The new device employs a novel silicon-based ultrasonic Nozzle with multiple Fourier horns in resonance designed to operate based on the phenomena of Faraday waves at the frequency range of 1 to 2.5 MHz. The superior performance and batch fabrication economy of the centimeter-size Nozzles have demonstrated the potential towards commercialization of the new delivery device.The Nozzle consists of a drive section and a resonator section. The resonator section is made of multiple Fourier horns in cascade. The Nozzle is designed to vibrate at the resonance frequency of the multiple Fourier horns. A lead zirconate titanate (PZT) piezoelectric transducer is bonded on the drive section to excite mechanical vibrations (displacement) along the Nozzle axis. The PZT transducers are fed by a driving circuit. The resultant vibration amplitude on the Nozzle End face (tip of the distal horn) is greatly magnified. As the liquid fed from a plastic tubing to the Nozzle’s tip, a liquid layer is maintained on the surface of the Nozzle tip to form standing capillary waves and production of monodisperse droplets when the tip vibration amplitude exceeds a threshold value. The major objective of this dissertation research is to devise and develop methods to accomplish a high level of performance and robustness for a standalone nebulization module. Significant advances have been made towards the objective
Rafet Yapici - One of the best experts on this subject based on the ideXlab platform.
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experimental study on ejector refrigeration system powered by low grade heat
Energy Conversion and Management, 2007Co-Authors: Rafet Yapici, C C YetisenAbstract:Abstract An ejector refrigeration system has been designed and constructed to operate with hot water. Such a refrigeration system, designed for low pressure refrigerants, can be operated using energy sources such as solar energy, geothermal energy and waste heat. In this study, the effects of the main operating parameters on system performance were experimentally investigated using R-11 as the working fluid and keeping constant the position of the primary Nozzle End at the inlet plane of the mixing chamber section of the ejector. The experimental study was performed over a range of vapor generator temperatures from about 90 to 102 °C, evaporator temperatures from 0 to 16 °C and condenser pressures from 114 to 143 kPa, and a COP up to 0.25 was obtained. It was seen that if higher cooling capacity and also lower evaporator temperature are desired from the system, the vapor generator temperature should be increased considerably.
