The Reynolds Averaged Navier-Stokes(RANS) models are still the workhorse in current engineering applications due to its high efficiency and robustness. However, the closure coefficients of RANS turbulence models are d...The Reynolds Averaged Navier-Stokes(RANS) models are still the workhorse in current engineering applications due to its high efficiency and robustness. However, the closure coefficients of RANS turbulence models are determined by model builders according to some simple fundamental flows, and the suggested values may not be applicable to complex flows, especially supersonic jet interaction flow. In this work, the Bayesian method is employed to recalibrate the closure coefficients of Spalart-Allmaras(SA) turbulence model to improve its performance in supersonic jet interaction problem and quantify the uncertainty of wall pressure and separation length. The embedded model error approach is applied to the Bayesian uncertainty analysis. Firstly, the total Sobol index is calculated by non-intrusive polynomial chaos method to represent the sensitivity of wall pressure and separation length to model parameters. Then, the pressure data and the separation length are respectively served as calibration data to get the posterior uncertainty of model parameters and Quantities of Interests(Qo Is). The results show that the relative error of the wall pressure predicted by the SA turbulence model can be reduced from 14.99% to 2.95% through effective Bayesian parameter estimation. Besides, the calibration effects of four likelihood functions are systematically evaluated. The posterior uncertainties of wall pressure and separation length estimated by different likelihood functions are significantly discrepant, and the Maximum a Posteriori(MAP) values of parameters inferred by all functions show better performance than the nominal values. Finally, the closure coefficients are also estimated at different jet total pressures. The similar posterior distributions of model parameters are obtained in different cases, and the MAP values of parameters calibrated in one case are also applicable to other cases.展开更多
Interaction flow field of the sonic air jet through diamond shaped orifices at different incidence angles （10 degrees, 27.5 degrees, 45 degrees and 90 degrees） and total pressures （0.10 MPa and 0. 46 MPa） with a M...Interaction flow field of the sonic air jet through diamond shaped orifices at different incidence angles （10 degrees, 27.5 degrees, 45 degrees and 90 degrees） and total pressures （0.10 MPa and 0. 46 MPa） with a Mach 5.0 freestream was studied experimentally. A 90 degrees circular injector was examined for comparison. Crosssection Mach number contours were acquired by a Pitot-cone five-hole pressure probe. The results indicate that the low Mach semicircular region close to the wall is the wake region. The boundary layer thinning is in the areas adjacent to the wake. For the detached case, the interaction shock extends further into the freestream, and the shock shape has more curvature, also the low-Mach upwash region is larger. The vortices of the plume and the height of the jet interaction shock increase with increasing incidence angle and jet pressure. 90 degrees diamond and circular injector have stronger plume vorticity, and for the circular injector low-Mach region is smaller than that for the diamond injector. Tapered ramp increases the plume vorticity, and the double ramp reduces the level of vorticity. The three-dimensional interaction shock shape was modeled from the surface shock shape, the center plane shock shape, and crosssectional shock shape. The shock total pressure was estimated with the normal component of the Mach number using normal shock theory. The shock induced total pressure losses decrease with decreasing jet incidence angle and injection pressure, where the largest losses are incurred by the 90 degrees, circular injector.展开更多
The paper focuses on the triple jets interaction with a hypersonic external flow on a revolution body. The experimental model is a ogive-cylinder body with three supersonic nozzles, which are aligned along the flow di...The paper focuses on the triple jets interaction with a hypersonic external flow on a revolution body. The experimental model is a ogive-cylinder body with three supersonic nozzles, which are aligned along the flow direction. The freestream Mach numbers are 5 and 6. The spatial and surface flow characteristics are illustrated by the schlieren photographs and the typical pressure distribution. The results show that there are multi-wave system, separation, reattachment, multi-peak pressure, high-pressure and low-pressure zone boundaries obvious distinction in tri-jets interference flowfield. The present paper also analyzes how do the pressure ratio, the angle of attack, and Mach number effect on tri-jets interaction characteristics.展开更多
The strong force effect on gluon distribution of quark-gluon plasma and its influence on jet energy loss with detailed balance are studied. We solve the possibility equation and obtain the value of non-extensive param...The strong force effect on gluon distribution of quark-gluon plasma and its influence on jet energy loss with detailed balance are studied. We solve the possibility equation and obtain the value of non-extensive parameter q. In the presence of strong interaction, more gluons stay at low-energy state than the free gluon case. The strong interaction effect is found to be important for jet energy loss with detailed balance at intermediate jet energy. The energy gain via absorption increases with the strong interaction. This will affect the nuclear modification factor RAA and the parameter of q at intermediate jet energy.展开更多
As one type of potential flow control actuators, cavity-actuated supersonic jet oscillators, which consist of a 2-D convergent nozzle and two face to face cavities, need to be investigated dee- ply to get the knowledg...As one type of potential flow control actuators, cavity-actuated supersonic jet oscillators, which consist of a 2-D convergent nozzle and two face to face cavities, need to be investigated dee- ply to get the knowledge of their oscillating feature and underlying mechanism. Wind tunnel testing are conducted under different back pressures in a vacuum-type wind tunnel for two supersonic jet oscillators, to obtain their characteristics and the conditions for jet oscillating. The experimental results show that the continuous, nearly symmetric or asymmetric flipping between the two cavities appears over certain nozzle pressure ratio （NPR） range for both oscillators according to schlieren visualizations. Compared to the free jet, the oscillating jet with large exit achieves larger mixing; the oscillating jet with small exit has less mixing, based on the analysis of jet axial peak velocity and the entrainment. The cross-junction mode for estimating the resonance frequency in a pipe with two closed side branches is modified and obtained comparable estimations of the frequency of jet flipping with experimental data, but further investigations are needed to discover the underlying mechanism for the jet flipping.展开更多
Wind tunnel testing is conducted at different back pressures in a vacuum-type wind tunnel for a novel supersonic fluidic oscillator which consists of a two-dimensional Laval nozzle, a rectangular cavity and a backward...Wind tunnel testing is conducted at different back pressures in a vacuum-type wind tunnel for a novel supersonic fluidic oscillator which consists of a two-dimensional Laval nozzle, a rectangular cavity and a backward step, to obtain its characteristics and the conditions for jet oscillating. The experimental results show that periodic asymmetrical flipping of the supersonic jet appears over certain nozzle pressure ratio（NPR） range according to schlieren visualization and pressure fluctuations. The jet flipping appears only when the jet is over expanded. The normalized average amplitude of the lateral pressure difference acting on the roofs of the cavity and the step varies around 0.2 while the periodic flipping appears. The supersonic jet periodic flipping frequencies obtained from the experiments agree well with those from the modified Rossiter mode for cavity-step acoustic resonance, but further investigations are needed to discover the underlying mechanism for the jet flipping.展开更多
Gaseous jets injected into water are typically found in underwater propulsion, and the flow is essentially unsteady and turbulent. Additionally, the high water-to-gas density ratio can result in complicated flow struc...Gaseous jets injected into water are typically found in underwater propulsion, and the flow is essentially unsteady and turbulent. Additionally, the high water-to-gas density ratio can result in complicated flow structures; hence measuring the flow structures numerically and experimentally remains a challenge. To investigate the performance of the underwater propulsion, this paper uses detailed NavierStokes flow computations to elucidate the gas-water interactions under the framework of the volume of fluid （VOF） model. Furthermore, these computations take the fluid compressibility, viscosity, and energy transfer into consideration. This paper compares the numerical results and experimental data, showing that phenomena including expansion, bulge, necking/breaking, and back-attack are highlighted in the jet process. The resulting analysis indicates that the pressure difference on the rear and front surfaces of the propul- sion system can generate an additional thrust. The strong and oscillatory thrust of the underwater propulsion system is caused by the intermittent pulses of the back pressure and the nozzle exit pressure. As a result, the total thrust in underwater propulsion is not only determined by the nozzle geometry but also by the flow structures and associated pressure distri- butions.展开更多
In the present work, computational simulations was made using ANSYS CFX to predict the improvements in film cooling performance with dual trench. Dual-trench confguradon consists of two trenches together, one wider tr...In the present work, computational simulations was made using ANSYS CFX to predict the improvements in film cooling performance with dual trench. Dual-trench confguradon consists of two trenches together, one wider trench and the other is narrow trench that extruded from the wider one. Several blowing ratios in the range （0.5：5） were investigated. The pitch-to-diameter ratio of 2.775 is used. By using the dual trench configuration, the coolant jet impacted the trench wall two times allowing increasing the spreading of coolant laterally in the trench, reducing jet velocity and jet completely covered on the surface. The results indicate that this configuration increased adiabatic effectiveness as blowing ratio increased. The spatially averaged adiabatic effectiveness reached 57.6% for at M= 2. No observed film blow-off at all blowing ratios. The adiabatic film effectiveness of dual trench case outperformed the narrow trench case, laidback fan-shaped hole, fan-shaped hole and cylinder hole at different blowing ratios.展开更多
基金supported by the National Numerical Windtunnel Project,China(No.NNW2019ZT1-A03)the National Natural Science Foundation of China(No.11721202)。
文摘The Reynolds Averaged Navier-Stokes(RANS) models are still the workhorse in current engineering applications due to its high efficiency and robustness. However, the closure coefficients of RANS turbulence models are determined by model builders according to some simple fundamental flows, and the suggested values may not be applicable to complex flows, especially supersonic jet interaction flow. In this work, the Bayesian method is employed to recalibrate the closure coefficients of Spalart-Allmaras(SA) turbulence model to improve its performance in supersonic jet interaction problem and quantify the uncertainty of wall pressure and separation length. The embedded model error approach is applied to the Bayesian uncertainty analysis. Firstly, the total Sobol index is calculated by non-intrusive polynomial chaos method to represent the sensitivity of wall pressure and separation length to model parameters. Then, the pressure data and the separation length are respectively served as calibration data to get the posterior uncertainty of model parameters and Quantities of Interests(Qo Is). The results show that the relative error of the wall pressure predicted by the SA turbulence model can be reduced from 14.99% to 2.95% through effective Bayesian parameter estimation. Besides, the calibration effects of four likelihood functions are systematically evaluated. The posterior uncertainties of wall pressure and separation length estimated by different likelihood functions are significantly discrepant, and the Maximum a Posteriori(MAP) values of parameters inferred by all functions show better performance than the nominal values. Finally, the closure coefficients are also estimated at different jet total pressures. The similar posterior distributions of model parameters are obtained in different cases, and the MAP values of parameters calibrated in one case are also applicable to other cases.
文摘Interaction flow field of the sonic air jet through diamond shaped orifices at different incidence angles （10 degrees, 27.5 degrees, 45 degrees and 90 degrees） and total pressures （0.10 MPa and 0. 46 MPa） with a Mach 5.0 freestream was studied experimentally. A 90 degrees circular injector was examined for comparison. Crosssection Mach number contours were acquired by a Pitot-cone five-hole pressure probe. The results indicate that the low Mach semicircular region close to the wall is the wake region. The boundary layer thinning is in the areas adjacent to the wake. For the detached case, the interaction shock extends further into the freestream, and the shock shape has more curvature, also the low-Mach upwash region is larger. The vortices of the plume and the height of the jet interaction shock increase with increasing incidence angle and jet pressure. 90 degrees diamond and circular injector have stronger plume vorticity, and for the circular injector low-Mach region is smaller than that for the diamond injector. Tapered ramp increases the plume vorticity, and the double ramp reduces the level of vorticity. The three-dimensional interaction shock shape was modeled from the surface shock shape, the center plane shock shape, and crosssectional shock shape. The shock total pressure was estimated with the normal component of the Mach number using normal shock theory. The shock induced total pressure losses decrease with decreasing jet incidence angle and injection pressure, where the largest losses are incurred by the 90 degrees, circular injector.
文摘The paper focuses on the triple jets interaction with a hypersonic external flow on a revolution body. The experimental model is a ogive-cylinder body with three supersonic nozzles, which are aligned along the flow direction. The freestream Mach numbers are 5 and 6. The spatial and surface flow characteristics are illustrated by the schlieren photographs and the typical pressure distribution. The results show that there are multi-wave system, separation, reattachment, multi-peak pressure, high-pressure and low-pressure zone boundaries obvious distinction in tri-jets interference flowfield. The present paper also analyzes how do the pressure ratio, the angle of attack, and Mach number effect on tri-jets interaction characteristics.
基金Supported by the National Natural Science Foundation of China under Grant No 11205024the Doctoral Scientific Fund Project of the Ministry of Education of China under Grant No 2012004112004
文摘The strong force effect on gluon distribution of quark-gluon plasma and its influence on jet energy loss with detailed balance are studied. We solve the possibility equation and obtain the value of non-extensive parameter q. In the presence of strong interaction, more gluons stay at low-energy state than the free gluon case. The strong interaction effect is found to be important for jet energy loss with detailed balance at intermediate jet energy. The energy gain via absorption increases with the strong interaction. This will affect the nuclear modification factor RAA and the parameter of q at intermediate jet energy.
基金supported by a grant from ‘‘Preeminence Program-Star of Zijin" of Nanjing University of Science and Technology – China. (No. AB41361)
文摘As one type of potential flow control actuators, cavity-actuated supersonic jet oscillators, which consist of a 2-D convergent nozzle and two face to face cavities, need to be investigated dee- ply to get the knowledge of their oscillating feature and underlying mechanism. Wind tunnel testing are conducted under different back pressures in a vacuum-type wind tunnel for two supersonic jet oscillators, to obtain their characteristics and the conditions for jet oscillating. The experimental results show that the continuous, nearly symmetric or asymmetric flipping between the two cavities appears over certain nozzle pressure ratio （NPR） range for both oscillators according to schlieren visualizations. Compared to the free jet, the oscillating jet with large exit achieves larger mixing; the oscillating jet with small exit has less mixing, based on the analysis of jet axial peak velocity and the entrainment. The cross-junction mode for estimating the resonance frequency in a pipe with two closed side branches is modified and obtained comparable estimations of the frequency of jet flipping with experimental data, but further investigations are needed to discover the underlying mechanism for the jet flipping.
基金supported by a grant from the Natural Science Foundation of Jiangsu Province (No. BK20150781)
文摘Wind tunnel testing is conducted at different back pressures in a vacuum-type wind tunnel for a novel supersonic fluidic oscillator which consists of a two-dimensional Laval nozzle, a rectangular cavity and a backward step, to obtain its characteristics and the conditions for jet oscillating. The experimental results show that periodic asymmetrical flipping of the supersonic jet appears over certain nozzle pressure ratio（NPR） range according to schlieren visualization and pressure fluctuations. The jet flipping appears only when the jet is over expanded. The normalized average amplitude of the lateral pressure difference acting on the roofs of the cavity and the step varies around 0.2 while the periodic flipping appears. The supersonic jet periodic flipping frequencies obtained from the experiments agree well with those from the modified Rossiter mode for cavity-step acoustic resonance, but further investigations are needed to discover the underlying mechanism for the jet flipping.
文摘Gaseous jets injected into water are typically found in underwater propulsion, and the flow is essentially unsteady and turbulent. Additionally, the high water-to-gas density ratio can result in complicated flow structures; hence measuring the flow structures numerically and experimentally remains a challenge. To investigate the performance of the underwater propulsion, this paper uses detailed NavierStokes flow computations to elucidate the gas-water interactions under the framework of the volume of fluid （VOF） model. Furthermore, these computations take the fluid compressibility, viscosity, and energy transfer into consideration. This paper compares the numerical results and experimental data, showing that phenomena including expansion, bulge, necking/breaking, and back-attack are highlighted in the jet process. The resulting analysis indicates that the pressure difference on the rear and front surfaces of the propul- sion system can generate an additional thrust. The strong and oscillatory thrust of the underwater propulsion system is caused by the intermittent pulses of the back pressure and the nozzle exit pressure. As a result, the total thrust in underwater propulsion is not only determined by the nozzle geometry but also by the flow structures and associated pressure distri- butions.
基金Supprted by Harbin Engineering University Scholarship under Grant No. 20100903D01
文摘In the present work, computational simulations was made using ANSYS CFX to predict the improvements in film cooling performance with dual trench. Dual-trench confguradon consists of two trenches together, one wider trench and the other is narrow trench that extruded from the wider one. Several blowing ratios in the range （0.5：5） were investigated. The pitch-to-diameter ratio of 2.775 is used. By using the dual trench configuration, the coolant jet impacted the trench wall two times allowing increasing the spreading of coolant laterally in the trench, reducing jet velocity and jet completely covered on the surface. The results indicate that this configuration increased adiabatic effectiveness as blowing ratio increased. The spatially averaged adiabatic effectiveness reached 57.6% for at M= 2. No observed film blow-off at all blowing ratios. The adiabatic film effectiveness of dual trench case outperformed the narrow trench case, laidback fan-shaped hole, fan-shaped hole and cylinder hole at different blowing ratios.
