The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
S Rosenwaks - One of the best experts on this subject based on the ideXlab platform.
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flowing gas diode pumped alkali lasers theoretical analysis of transonic vs supersonic and subsonic devices
Optics Express, 2016Co-Authors: Eyal Yacoby, Karol Waichman, O Sadot, Boris D Barmashenko, S RosenwaksAbstract:We examine transonic diode pumped alkali laser (DPAL) devices as a simpler alternative to supersonic devices, suggested by B.D. Barmashenko and S. Rosenwaks [Appl. Phys. Lett. 102, 141108 (2013)], where complex hardware, including supersonic nozzle, diffuser and high power mechanical pump, is required for continuous closed cycle operation. Three-dimensional computational fluid dynamics modeling of transonic (Mach number M ~0.9) Cs and K DPALs, taking into account the kinetic processes in the lasing medium is reported. The performance of these lasers is compared with that of supersonic (M ~2.5) and subsonic (M ~0.2) DPALs. For Cs DPAL the maximum achievable power of transonic device is lower than that of supersonic, with the same resonator and Cs density at the laser section inlet, by only ~3% implying that supersonic operation mode has only small advantage over transonic. On the other hand, for subsonic laser the maximum power is by 7% lower than in transonic, showing larger advantage of transonic over subsonic operation mode. The power achieved in supersonic and transonic K DPALs is higher than in subsonic by ~80% and ~20%, respectively, showing a considerable advantage of supersonic device over transonic and of transonic over subsonic.
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feasibility of supersonic diode pumped alkali lasers model calculations
Applied Physics Letters, 2013Co-Authors: Boris D Barmashenko, S RosenwaksAbstract:The feasibility of supersonic operation of diode pumped alkali lasers (DPALs) is studied for Cs and K atoms applying model calculations, based on a semi-analytical model previously used for studying static and subsonic flow DPALs. The operation of supersonic lasers is compared with that measured and modeled in subsonic lasers. The maximum power of supersonic Cs and K lasers is found to be higher than that of subsonic lasers with the same resonator and alkali density at the laser inlet by 25% and 70%, respectively. These results indicate that for scaling-up the power of DPALs, supersonic expansion should be considered.
Xiaolin Zhong - One of the best experts on this subject based on the ideXlab platform.
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sound radiation by supersonic unstable modes in hypersonic blunt cone boundary layers i linear stability theory
Physics of Fluids, 2019Co-Authors: Carleton P Knisely, Xiaolin ZhongAbstract:There has been renewed interest in supersonic modes in hypersonic boundary layers, which have been previously thought to be insignificant due to their smaller amplitudes than Mack’s traditional second mode. Supersonic modes are associated with an unstable second mode synchronizing with the slow acoustic spectrum, causing sound to radiate outwards from the boundary layer. Because supersonic modes have not been observed experimentally, the majority of previous investigations either relied on Linear Stability Theory (LST) to study supersonic modes on a flat plate or observed them in the context of other research objectives. This two-part study uses a combined LST and Direct Numerical Simulation (DNS) approach to investigate the mechanism of supersonic modes in Mach 5 flow over a blunt cold-wall cone with thermochemical nonequilibrium effects. Paper I focuses on LST with new shock boundary conditions, whereas Paper II [C.P. Knisely and X. Zhong, “Sound radiation by supersonic unstable modes in hypersonic blunt cone boundary layers. II. Direct numerical simulation,” Phys. Fluids 31, 024104 (2019)] focuses on DNS with the overall goal of investigating the impact of supersonic modes on transition. LST results indicate that supersonic modes exist in the flow with wall-to-free-stream temperature ratio Tw/T∞ = 0.2 and create an abnormal growth pattern. However, supersonic modes were not shown to exist using LST in the case with Tw/T∞ = 0.667. Subsequent DNS analysis in Paper II shows supersonic modes in the Tw/T∞ = 0.667 case, although they are significantly weaker than the second mode and are unlikely to lead to transition. Understanding the mechanism of supersonic modes can yield more accurate transition location predictions leading to improved estimates for drag and heat transfer to the vehicle.
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sound radiation by supersonic unstable modes in hypersonic blunt cone boundary layers i linear stability theory
Physics of Fluids, 2019Co-Authors: Carleton P Knisely, Xiaolin ZhongAbstract:There has been renewed interest in supersonic modes in hypersonic boundary layers, which have been previously thought to be insignificant due to their smaller amplitudes than Mack’s traditional second mode. Supersonic modes are associated with an unstable second mode synchronizing with the slow acoustic spectrum, causing sound to radiate outwards from the boundary layer. Because supersonic modes have not been observed experimentally, the majority of previous investigations either relied on Linear Stability Theory (LST) to study supersonic modes on a flat plate or observed them in the context of other research objectives. This two-part study uses a combined LST and Direct Numerical Simulation (DNS) approach to investigate the mechanism of supersonic modes in Mach 5 flow over a blunt cold-wall cone with thermochemical nonequilibrium effects. Paper I focuses on LST with new shock boundary conditions, whereas Paper II [C.P. Knisely and X. Zhong, “Sound radiation by supersonic unstable modes in hypersonic blunt cone boundary layers. II. Direct numerical simulation,” Phys. Fluids 31, 024104 (2019)] focuses on DNS with the overall goal of investigating the impact of supersonic modes on transition. LST results indicate that supersonic modes exist in the flow with wall-to-free-stream temperature ratio Tw/T∞ = 0.2 and create an abnormal growth pattern. However, supersonic modes were not shown to exist using LST in the case with Tw/T∞ = 0.667. Subsequent DNS analysis in Paper II shows supersonic modes in the Tw/T∞ = 0.667 case, although they are significantly weaker than the second mode and are unlikely to lead to transition. Understanding the mechanism of supersonic modes can yield more accurate transition location predictions leading to improved estimates for drag and heat transfer to the vehicle.There has been renewed interest in supersonic modes in hypersonic boundary layers, which have been previously thought to be insignificant due to their smaller amplitudes than Mack’s traditional second mode. Supersonic modes are associated with an unstable second mode synchronizing with the slow acoustic spectrum, causing sound to radiate outwards from the boundary layer. Because supersonic modes have not been observed experimentally, the majority of previous investigations either relied on Linear Stability Theory (LST) to study supersonic modes on a flat plate or observed them in the context of other research objectives. This two-part study uses a combined LST and Direct Numerical Simulation (DNS) approach to investigate the mechanism of supersonic modes in Mach 5 flow over a blunt cold-wall cone with thermochemical nonequilibrium effects. Paper I focuses on LST with new shock boundary conditions, whereas Paper II [C.P. Knisely and X. Zhong, “Sound radiation by supersonic unstable modes in hypersonic blun...
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sound radiation by supersonic unstable modes in hypersonic blunt cone boundary layers ii direct numerical simulation
Physics of Fluids, 2019Co-Authors: Carleton P Knisely, Xiaolin ZhongAbstract:Supersonic modes, previously thought to be insignificant due to their smaller amplitude than Mack’s traditional second mode, occur in hypersonic boundary layers when a disturbance travels supersonically with respect to the mean flow outside the boundary layer, causing outward-radiating acoustic waves. Very few previous studies perform Direct Numerical Simulation (DNS) of supersonic modes and instead rely on Linear Stability Theory (LST). This combined LST and DNS study investigates supersonic modes in Mach 5 flow over a blunt cold-wall cone. An LST analysis was performed in Paper I [C. P. Knisely and X. Zhong, “Sound radiation by supersonic unstable modes in hypersonic blunt cone boundary layers. I. Linear stability theory,” Phys. Fluids 31, 024103 (2019)], whereas DNS is the focus of Paper II. The overall goal is to determine the mechanism of supersonic modes and the conditions under which they exist. Compared to previous pure LST studies, DNS provides the advantage of making fewer limiting assumptions and can resolve interactions between modes. The results here indicate the excitation of supersonic modes via modal interactions not resolved with LST, suggesting the inadequacy of pure LST analyses concerning supersonic modes. Unsteady DNS results verified supersonic modes in the flow with wall-to-free-stream temperature ratio Tw/T∞ = 0.2, lending credence to the modes’ physical existence. However in the case of Tw/T∞ = 0.667, sound radiation was also found in DNS while LST predicted a stable supersonic mode. The mechanism for supersonic modes is attributed to a modal interaction between mode F1, mode S, and the slow acoustic spectrum. Therefore, it is necessary to perform combined LST and DNS studies of supersonic modes to reliably predict their presence and impact on transition to turbulence.Supersonic modes, previously thought to be insignificant due to their smaller amplitude than Mack’s traditional second mode, occur in hypersonic boundary layers when a disturbance travels supersonically with respect to the mean flow outside the boundary layer, causing outward-radiating acoustic waves. Very few previous studies perform Direct Numerical Simulation (DNS) of supersonic modes and instead rely on Linear Stability Theory (LST). This combined LST and DNS study investigates supersonic modes in Mach 5 flow over a blunt cold-wall cone. An LST analysis was performed in Paper I [C. P. Knisely and X. Zhong, “Sound radiation by supersonic unstable modes in hypersonic blunt cone boundary layers. I. Linear stability theory,” Phys. Fluids 31, 024103 (2019)], whereas DNS is the focus of Paper II. The overall goal is to determine the mechanism of supersonic modes and the conditions under which they exist. Compared to previous pure LST studies, DNS provides the advantage of making fewer limiting assumptions a...
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significant supersonic modes and the wall temperature effect in hypersonic boundary layers
AIAA Journal, 2019Co-Authors: Carleton P Knisely, Xiaolin ZhongAbstract:There has been renewed interest in studying supersonic modes in hypersonic boundary layers. Recent computational results have shown supersonic modes in hot-wall flows, upending the notion that they...
Boris D Barmashenko - One of the best experts on this subject based on the ideXlab platform.
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flowing gas diode pumped alkali lasers theoretical analysis of transonic vs supersonic and subsonic devices
Optics Express, 2016Co-Authors: Eyal Yacoby, Karol Waichman, O Sadot, Boris D Barmashenko, S RosenwaksAbstract:We examine transonic diode pumped alkali laser (DPAL) devices as a simpler alternative to supersonic devices, suggested by B.D. Barmashenko and S. Rosenwaks [Appl. Phys. Lett. 102, 141108 (2013)], where complex hardware, including supersonic nozzle, diffuser and high power mechanical pump, is required for continuous closed cycle operation. Three-dimensional computational fluid dynamics modeling of transonic (Mach number M ~0.9) Cs and K DPALs, taking into account the kinetic processes in the lasing medium is reported. The performance of these lasers is compared with that of supersonic (M ~2.5) and subsonic (M ~0.2) DPALs. For Cs DPAL the maximum achievable power of transonic device is lower than that of supersonic, with the same resonator and Cs density at the laser section inlet, by only ~3% implying that supersonic operation mode has only small advantage over transonic. On the other hand, for subsonic laser the maximum power is by 7% lower than in transonic, showing larger advantage of transonic over subsonic operation mode. The power achieved in supersonic and transonic K DPALs is higher than in subsonic by ~80% and ~20%, respectively, showing a considerable advantage of supersonic device over transonic and of transonic over subsonic.
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feasibility of supersonic diode pumped alkali lasers model calculations
Applied Physics Letters, 2013Co-Authors: Boris D Barmashenko, S RosenwaksAbstract:The feasibility of supersonic operation of diode pumped alkali lasers (DPALs) is studied for Cs and K atoms applying model calculations, based on a semi-analytical model previously used for studying static and subsonic flow DPALs. The operation of supersonic lasers is compared with that measured and modeled in subsonic lasers. The maximum power of supersonic Cs and K lasers is found to be higher than that of subsonic lasers with the same resonator and alkali density at the laser inlet by 25% and 70%, respectively. These results indicate that for scaling-up the power of DPALs, supersonic expansion should be considered.
Carleton P Knisely - One of the best experts on this subject based on the ideXlab platform.
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sound radiation by supersonic unstable modes in hypersonic blunt cone boundary layers i linear stability theory
Physics of Fluids, 2019Co-Authors: Carleton P Knisely, Xiaolin ZhongAbstract:There has been renewed interest in supersonic modes in hypersonic boundary layers, which have been previously thought to be insignificant due to their smaller amplitudes than Mack’s traditional second mode. Supersonic modes are associated with an unstable second mode synchronizing with the slow acoustic spectrum, causing sound to radiate outwards from the boundary layer. Because supersonic modes have not been observed experimentally, the majority of previous investigations either relied on Linear Stability Theory (LST) to study supersonic modes on a flat plate or observed them in the context of other research objectives. This two-part study uses a combined LST and Direct Numerical Simulation (DNS) approach to investigate the mechanism of supersonic modes in Mach 5 flow over a blunt cold-wall cone with thermochemical nonequilibrium effects. Paper I focuses on LST with new shock boundary conditions, whereas Paper II [C.P. Knisely and X. Zhong, “Sound radiation by supersonic unstable modes in hypersonic blunt cone boundary layers. II. Direct numerical simulation,” Phys. Fluids 31, 024104 (2019)] focuses on DNS with the overall goal of investigating the impact of supersonic modes on transition. LST results indicate that supersonic modes exist in the flow with wall-to-free-stream temperature ratio Tw/T∞ = 0.2 and create an abnormal growth pattern. However, supersonic modes were not shown to exist using LST in the case with Tw/T∞ = 0.667. Subsequent DNS analysis in Paper II shows supersonic modes in the Tw/T∞ = 0.667 case, although they are significantly weaker than the second mode and are unlikely to lead to transition. Understanding the mechanism of supersonic modes can yield more accurate transition location predictions leading to improved estimates for drag and heat transfer to the vehicle.
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sound radiation by supersonic unstable modes in hypersonic blunt cone boundary layers i linear stability theory
Physics of Fluids, 2019Co-Authors: Carleton P Knisely, Xiaolin ZhongAbstract:There has been renewed interest in supersonic modes in hypersonic boundary layers, which have been previously thought to be insignificant due to their smaller amplitudes than Mack’s traditional second mode. Supersonic modes are associated with an unstable second mode synchronizing with the slow acoustic spectrum, causing sound to radiate outwards from the boundary layer. Because supersonic modes have not been observed experimentally, the majority of previous investigations either relied on Linear Stability Theory (LST) to study supersonic modes on a flat plate or observed them in the context of other research objectives. This two-part study uses a combined LST and Direct Numerical Simulation (DNS) approach to investigate the mechanism of supersonic modes in Mach 5 flow over a blunt cold-wall cone with thermochemical nonequilibrium effects. Paper I focuses on LST with new shock boundary conditions, whereas Paper II [C.P. Knisely and X. Zhong, “Sound radiation by supersonic unstable modes in hypersonic blunt cone boundary layers. II. Direct numerical simulation,” Phys. Fluids 31, 024104 (2019)] focuses on DNS with the overall goal of investigating the impact of supersonic modes on transition. LST results indicate that supersonic modes exist in the flow with wall-to-free-stream temperature ratio Tw/T∞ = 0.2 and create an abnormal growth pattern. However, supersonic modes were not shown to exist using LST in the case with Tw/T∞ = 0.667. Subsequent DNS analysis in Paper II shows supersonic modes in the Tw/T∞ = 0.667 case, although they are significantly weaker than the second mode and are unlikely to lead to transition. Understanding the mechanism of supersonic modes can yield more accurate transition location predictions leading to improved estimates for drag and heat transfer to the vehicle.There has been renewed interest in supersonic modes in hypersonic boundary layers, which have been previously thought to be insignificant due to their smaller amplitudes than Mack’s traditional second mode. Supersonic modes are associated with an unstable second mode synchronizing with the slow acoustic spectrum, causing sound to radiate outwards from the boundary layer. Because supersonic modes have not been observed experimentally, the majority of previous investigations either relied on Linear Stability Theory (LST) to study supersonic modes on a flat plate or observed them in the context of other research objectives. This two-part study uses a combined LST and Direct Numerical Simulation (DNS) approach to investigate the mechanism of supersonic modes in Mach 5 flow over a blunt cold-wall cone with thermochemical nonequilibrium effects. Paper I focuses on LST with new shock boundary conditions, whereas Paper II [C.P. Knisely and X. Zhong, “Sound radiation by supersonic unstable modes in hypersonic blun...
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sound radiation by supersonic unstable modes in hypersonic blunt cone boundary layers ii direct numerical simulation
Physics of Fluids, 2019Co-Authors: Carleton P Knisely, Xiaolin ZhongAbstract:Supersonic modes, previously thought to be insignificant due to their smaller amplitude than Mack’s traditional second mode, occur in hypersonic boundary layers when a disturbance travels supersonically with respect to the mean flow outside the boundary layer, causing outward-radiating acoustic waves. Very few previous studies perform Direct Numerical Simulation (DNS) of supersonic modes and instead rely on Linear Stability Theory (LST). This combined LST and DNS study investigates supersonic modes in Mach 5 flow over a blunt cold-wall cone. An LST analysis was performed in Paper I [C. P. Knisely and X. Zhong, “Sound radiation by supersonic unstable modes in hypersonic blunt cone boundary layers. I. Linear stability theory,” Phys. Fluids 31, 024103 (2019)], whereas DNS is the focus of Paper II. The overall goal is to determine the mechanism of supersonic modes and the conditions under which they exist. Compared to previous pure LST studies, DNS provides the advantage of making fewer limiting assumptions and can resolve interactions between modes. The results here indicate the excitation of supersonic modes via modal interactions not resolved with LST, suggesting the inadequacy of pure LST analyses concerning supersonic modes. Unsteady DNS results verified supersonic modes in the flow with wall-to-free-stream temperature ratio Tw/T∞ = 0.2, lending credence to the modes’ physical existence. However in the case of Tw/T∞ = 0.667, sound radiation was also found in DNS while LST predicted a stable supersonic mode. The mechanism for supersonic modes is attributed to a modal interaction between mode F1, mode S, and the slow acoustic spectrum. Therefore, it is necessary to perform combined LST and DNS studies of supersonic modes to reliably predict their presence and impact on transition to turbulence.Supersonic modes, previously thought to be insignificant due to their smaller amplitude than Mack’s traditional second mode, occur in hypersonic boundary layers when a disturbance travels supersonically with respect to the mean flow outside the boundary layer, causing outward-radiating acoustic waves. Very few previous studies perform Direct Numerical Simulation (DNS) of supersonic modes and instead rely on Linear Stability Theory (LST). This combined LST and DNS study investigates supersonic modes in Mach 5 flow over a blunt cold-wall cone. An LST analysis was performed in Paper I [C. P. Knisely and X. Zhong, “Sound radiation by supersonic unstable modes in hypersonic blunt cone boundary layers. I. Linear stability theory,” Phys. Fluids 31, 024103 (2019)], whereas DNS is the focus of Paper II. The overall goal is to determine the mechanism of supersonic modes and the conditions under which they exist. Compared to previous pure LST studies, DNS provides the advantage of making fewer limiting assumptions a...
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significant supersonic modes and the wall temperature effect in hypersonic boundary layers
AIAA Journal, 2019Co-Authors: Carleton P Knisely, Xiaolin ZhongAbstract:There has been renewed interest in studying supersonic modes in hypersonic boundary layers. Recent computational results have shown supersonic modes in hot-wall flows, upending the notion that they...
Eyal Yacoby - One of the best experts on this subject based on the ideXlab platform.
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flowing gas diode pumped alkali lasers theoretical analysis of transonic vs supersonic and subsonic devices
Optics Express, 2016Co-Authors: Eyal Yacoby, Karol Waichman, O Sadot, Boris D Barmashenko, S RosenwaksAbstract:We examine transonic diode pumped alkali laser (DPAL) devices as a simpler alternative to supersonic devices, suggested by B.D. Barmashenko and S. Rosenwaks [Appl. Phys. Lett. 102, 141108 (2013)], where complex hardware, including supersonic nozzle, diffuser and high power mechanical pump, is required for continuous closed cycle operation. Three-dimensional computational fluid dynamics modeling of transonic (Mach number M ~0.9) Cs and K DPALs, taking into account the kinetic processes in the lasing medium is reported. The performance of these lasers is compared with that of supersonic (M ~2.5) and subsonic (M ~0.2) DPALs. For Cs DPAL the maximum achievable power of transonic device is lower than that of supersonic, with the same resonator and Cs density at the laser section inlet, by only ~3% implying that supersonic operation mode has only small advantage over transonic. On the other hand, for subsonic laser the maximum power is by 7% lower than in transonic, showing larger advantage of transonic over subsonic operation mode. The power achieved in supersonic and transonic K DPALs is higher than in subsonic by ~80% and ~20%, respectively, showing a considerable advantage of supersonic device over transonic and of transonic over subsonic.