The main purpose of this research is the second-order modeling of flow and turbulent heat flux in nonpremixed methane-air combustion.A turbulent stream of non-premixed combustion in a stoichiometric condition,is numer...The main purpose of this research is the second-order modeling of flow and turbulent heat flux in nonpremixed methane-air combustion.A turbulent stream of non-premixed combustion in a stoichiometric condition,is numerically analyzed through the Reynolds averaged Navier-Stokes(RANS) equations.For modeling radiation and combustion,the discrete ordinates(DO) and eddy dissipation concept model have been applied.The Reynolds stress transport model(RSM) also was used for turbulence modeling.For THF in the energy equation,the GGDH model and high order algebraic model of HOGGDH with simple eddy diffusivity model have been applied.Comparing the numerical results of the SED model(with the turbulent Prandtl 0.85) and the second-order heat flux models with available experimental data follows that applying the second-order models significantly led to the modification of predicting temperature distribution and species mass fraction distribution in the combustion chamber.Calculation of turbulent Prandtl number in the combustion chamber shows that the assumption of Pr_(t) of 0.85 is far from reality and Pr_(t) in different areas varies from 0.4 to 1.2.展开更多
The validity of the flow-mediated dilation (FMD) test has been doubted due to the lack of normalization to the primary stimulus, shear stress. Shear stress can be calculated using a simplified mathematical model based...The validity of the flow-mediated dilation (FMD) test has been doubted due to the lack of normalization to the primary stimulus, shear stress. Shear stress can be calculated using a simplified mathematical model based on Poiseuille’s law. Poiseuille’s law assumes that the blood velocity profile is parabolic. The presence of turbulence will violate this assumption. The Reynolds number (RE) is used to define critical values for the transition from laminar to turbulent flow. Between RE values of 2000 and 4000, flow enters a transitional phase where turbulence is possible. Purpose: To determine whether brachial artery blood flow becomes turbulent during reactive hyperemia following forearm ischemia. Methods: Eleven healthy male subjects (25 ± 5 years) were tested. Brachial artery diameters and blood velocities were measured continuously following 2, 4, 6 and 10 minutes ischemia. The peak post-ischemic RE (REpeak) and RE integrated over 40 seconds (RE40) post-ischemia were calculated. Results: There was a significant change in REpeak (F4,7 = 98.573, p = ≤ 0.001) and RE40) (F4,7) = 50.613, p = ≤ 0.001) in response to ischemia. Within-subjects contrasts revealed a significant increase in REpeak and RE40 for each duration of ischemia versus baseline (p = ≤ 0.001). Following 4 minutes of ischemia there was approximately 12 seconds of potentially turbulent flow. Conclusion: Blood flow transitions between laminar and turbulent flow during ischemia-induced reactive hyperemia. This may limit the efficacy of estimating shear stress when using the standard FMD test protocol.展开更多
文摘The main purpose of this research is the second-order modeling of flow and turbulent heat flux in nonpremixed methane-air combustion.A turbulent stream of non-premixed combustion in a stoichiometric condition,is numerically analyzed through the Reynolds averaged Navier-Stokes(RANS) equations.For modeling radiation and combustion,the discrete ordinates(DO) and eddy dissipation concept model have been applied.The Reynolds stress transport model(RSM) also was used for turbulence modeling.For THF in the energy equation,the GGDH model and high order algebraic model of HOGGDH with simple eddy diffusivity model have been applied.Comparing the numerical results of the SED model(with the turbulent Prandtl 0.85) and the second-order heat flux models with available experimental data follows that applying the second-order models significantly led to the modification of predicting temperature distribution and species mass fraction distribution in the combustion chamber.Calculation of turbulent Prandtl number in the combustion chamber shows that the assumption of Pr_(t) of 0.85 is far from reality and Pr_(t) in different areas varies from 0.4 to 1.2.
文摘The validity of the flow-mediated dilation (FMD) test has been doubted due to the lack of normalization to the primary stimulus, shear stress. Shear stress can be calculated using a simplified mathematical model based on Poiseuille’s law. Poiseuille’s law assumes that the blood velocity profile is parabolic. The presence of turbulence will violate this assumption. The Reynolds number (RE) is used to define critical values for the transition from laminar to turbulent flow. Between RE values of 2000 and 4000, flow enters a transitional phase where turbulence is possible. Purpose: To determine whether brachial artery blood flow becomes turbulent during reactive hyperemia following forearm ischemia. Methods: Eleven healthy male subjects (25 ± 5 years) were tested. Brachial artery diameters and blood velocities were measured continuously following 2, 4, 6 and 10 minutes ischemia. The peak post-ischemic RE (REpeak) and RE integrated over 40 seconds (RE40) post-ischemia were calculated. Results: There was a significant change in REpeak (F4,7 = 98.573, p = ≤ 0.001) and RE40) (F4,7) = 50.613, p = ≤ 0.001) in response to ischemia. Within-subjects contrasts revealed a significant increase in REpeak and RE40 for each duration of ischemia versus baseline (p = ≤ 0.001). Following 4 minutes of ischemia there was approximately 12 seconds of potentially turbulent flow. Conclusion: Blood flow transitions between laminar and turbulent flow during ischemia-induced reactive hyperemia. This may limit the efficacy of estimating shear stress when using the standard FMD test protocol.
