Numerical simulations are carried out for wave action on a submerged horizontal circular cylinder by means of a viscous fluid model, and it is focused on the examination of the discrepancies between the viscous fluid ...Numerical simulations are carried out for wave action on a submerged horizontal circular cylinder by means of a viscous fluid model, and it is focused on the examination of the discrepancies between the viscous fluid results and the potential flow solutions. It is found that the lift force resulted from rotational flow on the circular cylinder is always in anti-phase with the inertia force and induces the discrepancies between the results. The influence factors on the magnitude of the lift force, especially the correlation between the stagnation-point position and the wave amplitude, and the effect of the vortex shedding are investigated by further examination on the flow fields around the cylinder. The viscous numerical calculations at different wave frequencies showed that the wave frequency has also significant influence on the wave forces. Under higher frequency and larger amplitude wave action, vortex shedding from the circular cylinder will appear and influence the wave forces on the cylinder substantially.展开更多
An iterative and full-coupled rotor/fuselage aerodynamic interaction analytical method is developed based upon the rotor free-wake model and the 3-D fuselage panel model. A close vortex/ surface interaction model usin...An iterative and full-coupled rotor/fuselage aerodynamic interaction analytical method is developed based upon the rotor free-wake model and the 3-D fuselage panel model. A close vortex/ surface interaction model using the Analytical/Numerical Matching (ANM) was adopted in the method in order to simulate effectively the unsteady close interaction between the rotor tip-vortex and fuselage surface. By the analytical method, the unsteady and steady pressure distribution on the fuselage surface, and the unsteady lift and pitching moment of the fuselage in a rotor interaction environment were calculated for different advance ratios. It is shown that the unsteady aerodynamic loads of the fuselage due to the rotor interaction have the same periodic characteristics as the rotor. The comparisons between the present close vortex/surface interaction model and a previous model, which simply excludes vortex filaments inside the fuselage, were also made and the advantages of the former over the latter were demonstrated in improving unsteady close interaction calculations.展开更多
In this paper, 2-D computational analyses were conducted for unsteady high Reynolds number flows around a smooth circular cylinder in the supercritical and upper-transition flow regimes, i.e. 8.21×104〈Re〈1.54&#...In this paper, 2-D computational analyses were conducted for unsteady high Reynolds number flows around a smooth circular cylinder in the supercritical and upper-transition flow regimes, i.e. 8.21×104〈Re〈1.54×106. The calculations were performed by means of solving the 2-D Unsteady Reynolds-Averaged Navier-Stokes （URANS） equations with a k-ε turbulence model. The calculated results, produced flow structure drag and lift coefficients, as well as Strouhal numbers. The findings were in good agreement with previous published data, which also supplied us with a good understanding of the flow across cylinders of different high Reynolds numbers. Meanwhile, an effective measure was presented to control the lift force on a cylinder, which points the way to decrease the vortex induced vibration of marine structure in future.展开更多
Numerical simulation of wing stall of a blended flying wing configuration at transonic speed was conducted using both delayed detached eddy simulation（DDES） and unsteady Reynolds-averaged Navier-Stokes（URANS） equa...Numerical simulation of wing stall of a blended flying wing configuration at transonic speed was conducted using both delayed detached eddy simulation（DDES） and unsteady Reynolds-averaged Navier-Stokes（URANS） equations methods based on the shear stress transport（SST） turbulence model for a free-stream Mach number 0.9 and a Reynolds number 9.6 × 10. A joint time step/grid density study is performed based on power spectrum density（PSD） analysis of the frequency content of forces or moments, and medium mesh and the normalized time scale0.010 were suggested for this simulation. The simulation results show that the DDES methods perform more precisely than the URANS method and the aerodynamic coefficient results from DDES method compare very well with the experiment data. The angle of attack of nonlinear vortex lift and abrupt wing stall of DDES results compare well with the experimental data. The flow structure of the DDES computation shows that the wing stall is caused mainly by the leeward vortex breakdown which occurred at x/x= 0.6 at angle of attack of 14°. The DDES methods show advantage in the simulation problem with separation flow. The computed result shows that a shock/vortex interaction is responsible for the wing stall caused by the vortex breakdown. The balance of the vortex strength and axial flow, and the shock strength, is examined to provide an explanation of the sensitivity of the breakdown location. Wing body thickness has a great influence on shock and shock/vortex interactions, which can make a significant difference to the vortex breakdown behavior and stall characteristic of the blended flying wing configuration.展开更多
Wake separation is crucial to aircraft landing safety and is an important factor in airport operational efficiency.The near-ground evolution characteristics of wake vortices form the foundation of the wake separation ...Wake separation is crucial to aircraft landing safety and is an important factor in airport operational efficiency.The near-ground evolution characteristics of wake vortices form the foundation of the wake separation system design.In this study,we analysed the near-ground evolution of vortices in the wake of a domestic aircraft ARJ21 initialised by the lift-drag model using large eddy simulations based on an adaptive mesh.Evolution of wake vortices formed by the main wing,flap and horizontal tail was discussed in detail.The horizontal tail vortices are the weakest and dissipate rapidly,whereas the flap vortices are the strongest and induce the tip vortex to merge with them.The horizontal tail and flap of an ARJ21 do not significantly influence the circulation evolution,height change and movement trajectory of the wake vortices.The far-field evolution of wake vortices can therefore be analysed using the conventional wake vortex model.展开更多
For purpose of easy identification of the role of free vortices on the lift and drag and for purpose of fast or engineering evaluation of forces for each individual body, we will extend in this paper the Kutta-Joukows...For purpose of easy identification of the role of free vortices on the lift and drag and for purpose of fast or engineering evaluation of forces for each individual body, we will extend in this paper the Kutta-Joukowski （K J） theorem to the case of inviscid flow with multiple free vortices and multiple airfoils. The major simplification used in this paper is that each airfoil is represented by a lumped vortex, which may hold true when the distances between vortices and bodies are large enough. It is found that the Kutta-Joukowski theorem still holds provided that the local freestream velocity and the circulation of the bound vortex are modified by the induced velocity due to the out- side vortices and airfoils. We will demonstrate how to use the present result to identify the role of vortices on the forces according to their position, strength and rotation direction. Moreover, we will apply the present results to a two-cylinder example of Crowdy and the Wagner example to demon- strate how to perform fast force approximation for multi-body and multi-vortex problems. The lumped vortex assumption has the advantage of giving such kinds of approximate results which are very easy to use. The lack of accuracy for such a fast evaluation will be compensated by a rig- orous extension, with the lumped vortex assumption removed and with vortex production included, in a forthcoming paper.展开更多
The flow past two tandem circular cylinders of different diameters was simulated using the finite volume method. The diameter of the downstream main cylinder （D） was kept constant, and the diameter of the upstream c...The flow past two tandem circular cylinders of different diameters was simulated using the finite volume method. The diameter of the downstream main cylinder （D） was kept constant, and the diameter of the upstream control cylinder （d） varied from 0.1D to D. The studied Reynolds numbers based on the diameter of the downstream main cylinder were 100 and 150. The gap between the control cylinder and the main cylinder （G） ranged from 0.1D to 4D. It is concluded that the gap-to-diameter ratio （G/D） and the diameter ratio between the two cylinders （d/D） have important effects on the drag and lift coefficients, pressure distributions around the cylinders, vortex shedding frequencies from the two cylinders, and flow characteristics.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51490672 and 51761135011)the financial supports by the National Natural Science Foundation of China(Grant No.51490673)the Petro China Innovation Foundation(Grant No.2016D-5007-0601)
文摘Numerical simulations are carried out for wave action on a submerged horizontal circular cylinder by means of a viscous fluid model, and it is focused on the examination of the discrepancies between the viscous fluid results and the potential flow solutions. It is found that the lift force resulted from rotational flow on the circular cylinder is always in anti-phase with the inertia force and induces the discrepancies between the results. The influence factors on the magnitude of the lift force, especially the correlation between the stagnation-point position and the wave amplitude, and the effect of the vortex shedding are investigated by further examination on the flow fields around the cylinder. The viscous numerical calculations at different wave frequencies showed that the wave frequency has also significant influence on the wave forces. Under higher frequency and larger amplitude wave action, vortex shedding from the circular cylinder will appear and influence the wave forces on the cylinder substantially.
文摘An iterative and full-coupled rotor/fuselage aerodynamic interaction analytical method is developed based upon the rotor free-wake model and the 3-D fuselage panel model. A close vortex/ surface interaction model using the Analytical/Numerical Matching (ANM) was adopted in the method in order to simulate effectively the unsteady close interaction between the rotor tip-vortex and fuselage surface. By the analytical method, the unsteady and steady pressure distribution on the fuselage surface, and the unsteady lift and pitching moment of the fuselage in a rotor interaction environment were calculated for different advance ratios. It is shown that the unsteady aerodynamic loads of the fuselage due to the rotor interaction have the same periodic characteristics as the rotor. The comparisons between the present close vortex/surface interaction model and a previous model, which simply excludes vortex filaments inside the fuselage, were also made and the advantages of the former over the latter were demonstrated in improving unsteady close interaction calculations.
基金Foundation item： Supported by Supported by the National Natural Science Foundation of China （Grant No. 51009070）.
文摘In this paper, 2-D computational analyses were conducted for unsteady high Reynolds number flows around a smooth circular cylinder in the supercritical and upper-transition flow regimes, i.e. 8.21×104〈Re〈1.54×106. The calculations were performed by means of solving the 2-D Unsteady Reynolds-Averaged Navier-Stokes （URANS） equations with a k-ε turbulence model. The calculated results, produced flow structure drag and lift coefficients, as well as Strouhal numbers. The findings were in good agreement with previous published data, which also supplied us with a good understanding of the flow across cylinders of different high Reynolds numbers. Meanwhile, an effective measure was presented to control the lift force on a cylinder, which points the way to decrease the vortex induced vibration of marine structure in future.
基金supported by the National Natural Science Foundation of China (No. 11372337)
文摘Numerical simulation of wing stall of a blended flying wing configuration at transonic speed was conducted using both delayed detached eddy simulation（DDES） and unsteady Reynolds-averaged Navier-Stokes（URANS） equations methods based on the shear stress transport（SST） turbulence model for a free-stream Mach number 0.9 and a Reynolds number 9.6 × 10. A joint time step/grid density study is performed based on power spectrum density（PSD） analysis of the frequency content of forces or moments, and medium mesh and the normalized time scale0.010 were suggested for this simulation. The simulation results show that the DDES methods perform more precisely than the URANS method and the aerodynamic coefficient results from DDES method compare very well with the experiment data. The angle of attack of nonlinear vortex lift and abrupt wing stall of DDES results compare well with the experimental data. The flow structure of the DDES computation shows that the wing stall is caused mainly by the leeward vortex breakdown which occurred at x/x= 0.6 at angle of attack of 14°. The DDES methods show advantage in the simulation problem with separation flow. The computed result shows that a shock/vortex interaction is responsible for the wing stall caused by the vortex breakdown. The balance of the vortex strength and axial flow, and the shock strength, is examined to provide an explanation of the sensitivity of the breakdown location. Wing body thickness has a great influence on shock and shock/vortex interactions, which can make a significant difference to the vortex breakdown behavior and stall characteristic of the blended flying wing configuration.
基金financial support from the National Natural Science Foundation of China(Grant 91752205)Civil Aviation Joint Fund of NSFC(Grant U1733203)Civil Aviation Safety Capacity Building Project(Grant TM 2019-16-1/3)。
文摘Wake separation is crucial to aircraft landing safety and is an important factor in airport operational efficiency.The near-ground evolution characteristics of wake vortices form the foundation of the wake separation system design.In this study,we analysed the near-ground evolution of vortices in the wake of a domestic aircraft ARJ21 initialised by the lift-drag model using large eddy simulations based on an adaptive mesh.Evolution of wake vortices formed by the main wing,flap and horizontal tail was discussed in detail.The horizontal tail vortices are the weakest and dissipate rapidly,whereas the flap vortices are the strongest and induce the tip vortex to merge with them.The horizontal tail and flap of an ARJ21 do not significantly influence the circulation evolution,height change and movement trajectory of the wake vortices.The far-field evolution of wake vortices can therefore be analysed using the conventional wake vortex model.
基金supported by National Basic Research Program of China (2012CB720205)
文摘For purpose of easy identification of the role of free vortices on the lift and drag and for purpose of fast or engineering evaluation of forces for each individual body, we will extend in this paper the Kutta-Joukowski （K J） theorem to the case of inviscid flow with multiple free vortices and multiple airfoils. The major simplification used in this paper is that each airfoil is represented by a lumped vortex, which may hold true when the distances between vortices and bodies are large enough. It is found that the Kutta-Joukowski theorem still holds provided that the local freestream velocity and the circulation of the bound vortex are modified by the induced velocity due to the out- side vortices and airfoils. We will demonstrate how to use the present result to identify the role of vortices on the forces according to their position, strength and rotation direction. Moreover, we will apply the present results to a two-cylinder example of Crowdy and the Wagner example to demon- strate how to perform fast force approximation for multi-body and multi-vortex problems. The lumped vortex assumption has the advantage of giving such kinds of approximate results which are very easy to use. The lack of accuracy for such a fast evaluation will be compensated by a rig- orous extension, with the lumped vortex assumption removed and with vortex production included, in a forthcoming paper.
基金supported by the National Natural Science Foundation of China(Grant No.40871050)
文摘The flow past two tandem circular cylinders of different diameters was simulated using the finite volume method. The diameter of the downstream main cylinder （D） was kept constant, and the diameter of the upstream control cylinder （d） varied from 0.1D to D. The studied Reynolds numbers based on the diameter of the downstream main cylinder were 100 and 150. The gap between the control cylinder and the main cylinder （G） ranged from 0.1D to 4D. It is concluded that the gap-to-diameter ratio （G/D） and the diameter ratio between the two cylinders （d/D） have important effects on the drag and lift coefficients, pressure distributions around the cylinders, vortex shedding frequencies from the two cylinders, and flow characteristics.
