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| 1 | Experimental study on correlation between turbulence and sound in a subsonic wind tunnel显示文摘In this paper,the effects of turbulence on sound generation and velocity fluctuations due to pressure waves in a large subsonic wind tunnel are studied.A trip strip located at different positions in the contraction part or at one position in the diffuser of a large wind tunnel is used to investigate the aforementioned phenomenon,and the results indicate that the trip strip has significant effects on sound reduction.The lowest turbulence intensity and sound are obtained from a trip strip with a diameter of 0.91mm located either at X/L = 0.79 or at X/L = 0.115 in the wide portion of the contraction.Furthermore,the effect of monopole,dipole and quadrupole sources of aerodynamic noise at different velocities is investigated,and it is demonstrated that the contribution of the monopole is dominant,while the shares due to the dipole and quadrupole remain less important.In addition,it is found that the sound waves have a modest impact on the measured longitudinal turbulence and are generated essentially by eddies. | M.D.Manshadi K.Ghorbanian M.R.Soltani | 2010 | Acta Mechanica Sinica2010，26，4： | 1 |
| 2 | Axisymmetric and three-dimensional flow simulation of a mixed compression supersonic air inlet显示文摘The flow through an axisymmetric supersonic mixed-compression air inlet has been simulated numerically to investigate the effects and the necessity of the three-dimensional(3D)modeling in comparison with the axisymmetric one.For this purpose,a supersonic inlet has been simulated numerically via axisymmetric and 3D CFD solvers,using the steady state Reynolds-averaged Navier-Stokes equations along with the SST k-ωturbulence model,for a free-stream Mach number of 2.0 and at zero degrees angle of attack.The grid for the 3D cases was a 14.4-degree sector,instead of a 360-degree domain one,with rotational periodic boundary condition for the side boundaries.The results show that both static and total pressure distributions match well with the experimental data for both the axisymmetric and the 3D simulations.If the prediction of performance parameters is the main goal of simulations,it seems that the axisymmetric simulation provides adequate accuracy,and the 3D simulation one is not the best choice.The 3D numerical simulation results in an in-depth study on the supersonic inlets,including the shock wave-boundary layer interaction,the location of the terminal normal shock wave,and consequently the separation point.For an axisymmetric supersonic inlet in an axisymmetric flow condition,3D effects are not strong enough to have a significant influence on the inlet performance for all operational conditions.However,it seems that 3D effects play an important role in both critical and supercritical operating conditions during the steady state operation. | M.Abedi R.Askari J.Sepahi-Younsi M.R.Soltani | 2020 | Propulsion and Power Research2020，9，1： | 1 |
| 3 | Impact of reduced frequency on the time lag in pressure distribution over a supercritical airfoil in a pitch-pause-return motion显示文摘Effects of reduced frequency, stop angle, and pause duration have been studied on a thin supercritical airfoil undergoing a pitch-pause-return motion, which is one of the classic maneuvers introduced by the AIAA Fluid Dynamics Technical Committee. Experiments were conducted in a low-speed wind tunnel at both a constant mean angle of attack and an oscillation amplitude with a reduced frequency ranging from 0.01 to 0.12. The desired stop angles of the airfoil were set to occur during the upstroke motion. The unsteady pressure distribution on the airfoil was measured for below, near, and beyond static stall conditions. Results showed that the reduced frequency and stop angle were the dominant contributors to the time lag in the flowfield. For stop angles in both belowand post-stall regions, the time for the flowfield to reach its steady state conditions, known as the time lag, decreased as the reduced frequency was increased. However, in the static-stall region and for a certain value of reduced frequency, a resonance phenomenon was observed, and a minimum time lag was achieved. The pressure distribution in this condition was shown to be highly influenced by this phenomenon. | Haghighat Z.ESLAMI Ali R.DAVARI M.R.SOLTANI | 2019 | Chinese Journal of Aeronautics2019，32，2： | 0 |
| 4 | Experimental study of the boundary layer over an airfoil in plunging motion显示文摘This is an experimental study on the boundary layer over an airfoil under steady and unsteady conditions.It specifically deals with the effect of plunging oscillation on the laminar/turbulent characteristics of the boundary layer.The wind tunnel measurements involved surfacemounted hot-film sensors and boundary-layer rake.The experiments were conducted at Reynolds numbers of 0.42×10 6 to 0.84 × 10 6 and the reduced frequency was varied from 0.01 to 0.11.The results of the quasi-wall-shear stress as well as the boundary layer velocity profiles provided important information about the state of the boundary layer over the suction surface of the airfoil in both static and dynamic cases.For the static tests,boundary layer transition occurred through a laminar separation bubble.By increasing the angle of attack,disturbances and the transition location moved toward the leading edge.For the dynamic tests,earlier transition occurred with increasing rather than decreasing effective angle of attack.The mean angle of attack and the oscillating parameters significantly affected the state of the boundary layer.By increasing the reduced frequency,the boundary layer transition was promoted to the upstroke portion of the equivalent angle of attack,but the quasi skin friction coefficient was decreased. | F.Rasi Marzabadi M.R.Soltani | 2012 | Acta Mechanica Sinica2012，28，2： | 0 |
| 5 | Effects of Mach numbers on Magnus induced surface pressure显示文摘Experimental and numerical methods were used to investigate the Magnus phenomena over a spinning projectile.The pressure force acting on the surface of a spinning projectile was measured for various cases by employing a relatively novel experimental technique.A set of miniature pressure sensors along with a data acquisition board,battery and storage memory were placed inside a spinning model and the surface pressure were obtained through a remotely controlled system.Circumferential pressures of the model for both rotational and static conditions were obtained at two different free stream Mach numbers of 0.4 and 0.8 and at different angles of attack.The results showed the ability of this new test method to measure the very small Magnus force via surface pressures over the projectile.The results provide a deep insight into the flow structure and illustrate changes in the cross-flow separation locations as a result of rotation.Similar results were obtained by the numerical simulations and were compared with the experimental data. | F.ASKARY M.R.SOLTANI | 2020 | Chinese Journal of Aeronautics2020，33，12： | 0 |
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