The fractional calculus approach in the constitutive relationship model of a generalized second grade fluid is introduced.Exact analytical solutions are obtained for a class of unsteady flows for the generalized secon...The fractional calculus approach in the constitutive relationship model of a generalized second grade fluid is introduced.Exact analytical solutions are obtained for a class of unsteady flows for the generalized second grade fluid with the fractional derivative model between two parallel plates by using the Laplace transform and Fourier transform for fractional calculus.The unsteady flows are generated by the impulsive motion or periodic oscillation of one of the plates.In addition,the solutions of the shear stresses at the plates are also determined.展开更多
Pressure wave propagation along a pipe attached with an activepressure-controlling system at an end was described by an unsteady state-changing motion of thepressure wave fronts, in order to study the interaction amon...Pressure wave propagation along a pipe attached with an activepressure-controlling system at an end was described by an unsteady state-changing motion of thepressure wave fronts, in order to study the interaction among successive waves caused by successivecontrolling spillovers with the consideration of liquid compressibility due to high head. A modelfor water hammer propagation was established by using the continuity, momentum, and energyequations. The influence of the wave interactions on the pressure suppression was analyzed. Testingverifications were conducted with a 2575m length and 776m head penstock in hydro-power station. Thecomputed results are in good agrement with the tested ones.展开更多
This study concerns the characterization of both the steady and unsteady flows and the analysis of stator/rotor interactions of a two-stage axial turbine. The predicted aerodynamic performances show noticeable differe...This study concerns the characterization of both the steady and unsteady flows and the analysis of stator/rotor interactions of a two-stage axial turbine. The predicted aerodynamic performances show noticeable differences when simulating the turbine stages simultaneously or separately. By considering the multi-blade per row and the scaling technique, the Computational fluid dynamics(CFD) produced better results concerning the effect of pitchwise positions between vanes and blades. The recorded pressure fluctuations exhibit a high unsteadiness characterized by a space–time periodicity described by a double Fourier decomposition. The Fast Fourier Transform FFT analysis of the static pressure fluctuations recorded at different interfaces reveals the existence of principal harmonics and their multiples, and each lobed structure of pressure wave corresponds to the number of vane/blade count. The potential effect is seen to propagate both upstream and downstream of each blade row and becomes accentuated at low mass flow rates. Between vanes and blades, the potential effect is seen to dominate the quasi totality of blade span, while downstream the blades this effect seems to dominate from hub to mid span. Near the shroud the prevailing effect is rather linked to the blade tip flow structure.展开更多
基金The project supported by the National Natural Science Foundation of China (10372007,10002003) and CNPC Innovation Fund
文摘The fractional calculus approach in the constitutive relationship model of a generalized second grade fluid is introduced.Exact analytical solutions are obtained for a class of unsteady flows for the generalized second grade fluid with the fractional derivative model between two parallel plates by using the Laplace transform and Fourier transform for fractional calculus.The unsteady flows are generated by the impulsive motion or periodic oscillation of one of the plates.In addition,the solutions of the shear stresses at the plates are also determined.
文摘Pressure wave propagation along a pipe attached with an activepressure-controlling system at an end was described by an unsteady state-changing motion of thepressure wave fronts, in order to study the interaction among successive waves caused by successivecontrolling spillovers with the consideration of liquid compressibility due to high head. A modelfor water hammer propagation was established by using the continuity, momentum, and energyequations. The influence of the wave interactions on the pressure suppression was analyzed. Testingverifications were conducted with a 2575m length and 776m head penstock in hydro-power station. Thecomputed results are in good agrement with the tested ones.
文摘This study concerns the characterization of both the steady and unsteady flows and the analysis of stator/rotor interactions of a two-stage axial turbine. The predicted aerodynamic performances show noticeable differences when simulating the turbine stages simultaneously or separately. By considering the multi-blade per row and the scaling technique, the Computational fluid dynamics(CFD) produced better results concerning the effect of pitchwise positions between vanes and blades. The recorded pressure fluctuations exhibit a high unsteadiness characterized by a space–time periodicity described by a double Fourier decomposition. The Fast Fourier Transform FFT analysis of the static pressure fluctuations recorded at different interfaces reveals the existence of principal harmonics and their multiples, and each lobed structure of pressure wave corresponds to the number of vane/blade count. The potential effect is seen to propagate both upstream and downstream of each blade row and becomes accentuated at low mass flow rates. Between vanes and blades, the potential effect is seen to dominate the quasi totality of blade span, while downstream the blades this effect seems to dominate from hub to mid span. Near the shroud the prevailing effect is rather linked to the blade tip flow structure.
