To investigate the influence of bluff body shape on wall pressure distribution in a vortex flowmeter,experiments were conducted on a specially designed test section in a closed water rig at Reynolds numbers of 6.2...To investigate the influence of bluff body shape on wall pressure distribution in a vortex flowmeter,experiments were conducted on a specially designed test section in a closed water rig at Reynolds numbers of 6.2×10 4-9.3×10 4.The cross sections of the bluff bodies were semicircular,square,and triangular shaped,and there were totally 21 pressure tappings along the conduit to acquire the wall pressures.It is found that the variation trends of wall pressures are basically identical regardless of the bluff body shapes.The wall pressures begin to diverge from 0.3D(D is the inner diameter of the vortex flowmeter) in front of the bluff body due to the diversity in shape,and all reach the minimum values at 0.3D behind the bluff body.A discrepancy between the triangular or square cylinder and the semicircular cylinder in wall pressure change is observed at 0-0.1D behind the bluff body.It is also found that the wall pressures and irrecoverable pressure loss coefficients increase with flow rates,and the triangular cylinder causes the smallest irrecoverable pressure loss at a fixed flow rate.展开更多
Turbulent kinetic energy budgets are presented for a highly curved flow generated by the collision of plane wall turbulent jet with a low-velocity boundary layer. The different terms are obtained in the vertical plane...Turbulent kinetic energy budgets are presented for a highly curved flow generated by the collision of plane wall turbulent jet with a low-velocity boundary layer. The different terms are obtained in the vertical plane of symmetry by quadratic interpolation of the LDV （Laser Doppler Velocimetry） measurements, for a wall jet-to-boundary layer velocity ratio of 2. The results, which have relevance to flows encountered in powered-lift aircraft operating in ground effect, quantify the structure of the complex ground vortex flow. The analysis of turbulent energy equation terms using the measured data revealed that production by normal and shear stresses are both very important to the turbulent structure of the impact zone of the ground vortex. This is an indication that the modeling of turbulence of a ground vortex requires a good representation of the production by normal stresses which is most important in the collision zone.展开更多
Flow separation in a conical diffuser with large divergence angle （29.14°） and large area ratio （3.533） is eliminated by a novel passive flow control device called Karman-Vortex Generator （KVG）. The effect ...Flow separation in a conical diffuser with large divergence angle （29.14°） and large area ratio （3.533） is eliminated by a novel passive flow control device called Karman-Vortex Generator （KVG）. The effect of the KVG is verified and investigated by the URANS, DES and DDES methods based on the SST model. CFD results show that the performance coefficient of the diffuser can be doubled by the KVG, and the total pressure recovery coefficient can be improved by about 1.2%. DES and DDES re- suits show that the KVG can introduce a Karman-vortex street frequency in the diffuser. This frequency decays rapidly, and could not be detected in the ending plane of the expansion section, Different KVG configurations with different locations and dimensions are numerically simulated and compared. Some suggestions are provided.展开更多
The two-dimensional flows around a cylinder between two parallel walls at Re=40 and Re=100 are simulated with computational fluid dynamics(CFD). The governing equations are Navier-Stokes equations. They are discretize...The two-dimensional flows around a cylinder between two parallel walls at Re=40 and Re=100 are simulated with computational fluid dynamics(CFD). The governing equations are Navier-Stokes equations. They are discretized with finite volume method(FVM) and the solution is iterated with PISO Algorithm. Then, the calculating results are compared with the numerical results in literature, and good agreements are obtained. After that, the mechanism of the formation of Karman vortex street is investigated and the instability of the entire flow field is analyzed with the energy gradient theory. It is found that the two eddies attached at the rear of the cylinder have no effect on the flow instability for steady flow, i.e., they don't contribute to the formation of Karman vortex street. The formation of Karman vortex street originates from the combinations of the interaction of two shear layers at two lateral sides of the cylinder and the absolute instability in the cylinder wake. For the flow with Karman vortex street, the initial instability occurs at the region in a vortex downstream of the wake and the center of a vortex firstly loses its stability in a vortex. For pressure driven flow, it is confirmed that the inflection point on the time-averaged velocity profile leads to the instability. It is concluded that the energy gradient theory is potentially applicable to study the flow stability and to reveal the mechanism of turbulent transition.展开更多
基金Project(51006125) supported by the National Natural Science Foundation of China
文摘To investigate the influence of bluff body shape on wall pressure distribution in a vortex flowmeter,experiments were conducted on a specially designed test section in a closed water rig at Reynolds numbers of 6.2×10 4-9.3×10 4.The cross sections of the bluff bodies were semicircular,square,and triangular shaped,and there were totally 21 pressure tappings along the conduit to acquire the wall pressures.It is found that the variation trends of wall pressures are basically identical regardless of the bluff body shapes.The wall pressures begin to diverge from 0.3D(D is the inner diameter of the vortex flowmeter) in front of the bluff body due to the diversity in shape,and all reach the minimum values at 0.3D behind the bluff body.A discrepancy between the triangular or square cylinder and the semicircular cylinder in wall pressure change is observed at 0-0.1D behind the bluff body.It is also found that the wall pressures and irrecoverable pressure loss coefficients increase with flow rates,and the triangular cylinder causes the smallest irrecoverable pressure loss at a fixed flow rate.
文摘Turbulent kinetic energy budgets are presented for a highly curved flow generated by the collision of plane wall turbulent jet with a low-velocity boundary layer. The different terms are obtained in the vertical plane of symmetry by quadratic interpolation of the LDV （Laser Doppler Velocimetry） measurements, for a wall jet-to-boundary layer velocity ratio of 2. The results, which have relevance to flows encountered in powered-lift aircraft operating in ground effect, quantify the structure of the complex ground vortex flow. The analysis of turbulent energy equation terms using the measured data revealed that production by normal and shear stresses are both very important to the turbulent structure of the impact zone of the ground vortex. This is an indication that the modeling of turbulence of a ground vortex requires a good representation of the production by normal stresses which is most important in the collision zone.
基金supported by the National Natural Science Foundation of China (Grant Nos.10932005,10972120 and 11102098)the China Postdoctoral Science Foundation (Grant No.2011M500301)
文摘Flow separation in a conical diffuser with large divergence angle （29.14°） and large area ratio （3.533） is eliminated by a novel passive flow control device called Karman-Vortex Generator （KVG）. The effect of the KVG is verified and investigated by the URANS, DES and DDES methods based on the SST model. CFD results show that the performance coefficient of the diffuser can be doubled by the KVG, and the total pressure recovery coefficient can be improved by about 1.2%. DES and DDES re- suits show that the KVG can introduce a Karman-vortex street frequency in the diffuser. This frequency decays rapidly, and could not be detected in the ending plane of the expansion section, Different KVG configurations with different locations and dimensions are numerically simulated and compared. Some suggestions are provided.
基金supported by the Natural Science Foundation of Zhejiang Province LY14E060003 )the Special Major Project of Science and Technology of Zhejiang Province (No.2013C01139)+1 种基金Zhejiang Province Key Science and Technology Innovation Team (2 013TD18)the Science Foundation of Zhejiang Sci-Tech University (No.11130032661215)
文摘The two-dimensional flows around a cylinder between two parallel walls at Re=40 and Re=100 are simulated with computational fluid dynamics(CFD). The governing equations are Navier-Stokes equations. They are discretized with finite volume method(FVM) and the solution is iterated with PISO Algorithm. Then, the calculating results are compared with the numerical results in literature, and good agreements are obtained. After that, the mechanism of the formation of Karman vortex street is investigated and the instability of the entire flow field is analyzed with the energy gradient theory. It is found that the two eddies attached at the rear of the cylinder have no effect on the flow instability for steady flow, i.e., they don't contribute to the formation of Karman vortex street. The formation of Karman vortex street originates from the combinations of the interaction of two shear layers at two lateral sides of the cylinder and the absolute instability in the cylinder wake. For the flow with Karman vortex street, the initial instability occurs at the region in a vortex downstream of the wake and the center of a vortex firstly loses its stability in a vortex. For pressure driven flow, it is confirmed that the inflection point on the time-averaged velocity profile leads to the instability. It is concluded that the energy gradient theory is potentially applicable to study the flow stability and to reveal the mechanism of turbulent transition.
