8 items pinned
Supersonic steady aerodynamics of a cylinder with a fluid flare
Abstract: Abstract Basing upon the ideal inviscid perfect gas model the aerodynamic characteristics and the gasdynamic function distributions over the surface of a cylinder in a steady supersonic three-dimensional flow are studied in the absence and the presence of combined intense air injection from the flat-ended nose and the lateral surface of the body into the shock layer. The purpose of the study is to investigate the influence of gas injection from different regions of the cylinder surface on supersonic flow past the cylinder at different angles of attack.AbstractBasing upon the ideal inviscid perfect gas model the aerodynamic characteristics and the gasdynamic function distributions over the surface of a cylinder in a steady supersonic three-dimensional flow are studied in the absence and the presence of combined intense air injection from the flat-ended nose and the lateral surface of the body into the shock layer. The purpose of the study is to investigate the influence of gas injection from different regions of the cylinder surface on supersonic flow past the cylinder at different angles of attack.
Pub.: 01 Nov '16, Pinned: 12 Apr '17
Drag reduction for the combination of spike and counterflow jet on blunt body at high Mach number flow
Abstract: Drag reduction at high speed flows around blunt bodies is one of the major challenges in the field of aerodynamics. Using of spikes and counterflow jets each of them separately for reducing of drag force is well known. The present work is description of flow field around a hemispherical nose cylinder with a new combination of spike and counterflow jet at free stream of Mach number of 6.The air gas was injected through the nozzle at the nose of the hemispherical model at sonic speed. In this numerical analysis, axisymmetric Reynolds-averaged Navier-Stokes equations was solved by k-ω (SST) turbulence model. The results were validated with experimental results for spiked body without jet condition. Then the results presented for different lengths of spike and different pressures of counterflow jets. The results show a significant reduction in the drag coefficient about 86–90% compared to the spherical cylinder model without jet and spike for practical models (L/D=1.5 and 2). Furthermore also our results indicate that the drag reduction is increased even more with increasing of the length of the spike.
Pub.: 12 Jan '17, Pinned: 12 Apr '17
An adaptive fully-Lagrangian meshless method for incompressible laminar flow airfoil studies
Abstract: Laminar incompressible flow around a NACA0012 airfoil placed in a free-stream at various incidences has been revisited with the use of a fully-Lagrangian meshless method based on a Smoothed Particle Hydrodynamics (SPH) formulation. Spatial adaptivity has been incorporated in the scheme via splitting and merging of SPH particles employing zonal criteria. In addition, a novel algorithm has been proposed here so that particle merging may be achieved, ensuring the robustness, accuracy and efficiency of the computational simulations. The results obtained have been benchmarked against available data from mesh-based methods. Good agreement has been found both in steady and unsteady flow regimes. Overall, the present work demonstrated the effectiveness and competitiveness of this meshfree approach for detailed studies in aerodynamics.
Pub.: 07 Feb '17, Pinned: 12 Apr '17
The Design of Steady State Schemes for Computational Aerodynamics
Abstract: Publication date: Available online 5 January 2017 Source:Handbook of Numerical Analysis Author(s): F.D. Witherden, A. Jameson, D.W. Zingg The majority of industrial computational fluid dynamics simulations are steady. Such simulations therefore require numerical methods which can rapidly converge a boundary value problem, typically either the Euler or Reynolds-averaged Navier–Stokes (RANS) equations. In this chapter we outline two major approaches: time-marching methods built on top of Runge–Kutta time-stepping schemes and Newton–Krylov methods. A range of techniques for accelerating convergence are presented including local time-stepping, enthalpy damping, residual averaging, multigrid methods and preconditioning. More recent hybrid approaches such as the Runge–Kutta symmetric Gauss–Seidel are also discussed. The effectiveness of these methodologies, within the context of several Euler and RANS test cases, is also evaluated.
Pub.: 09 Jan '17, Pinned: 12 Apr '17
Variation in Aerodynamic Coefficients with Altitude
Abstract: Precise aerodynamics performance prediction plays key role for a flying vehicle to get its mission completed within desired accuracy. Aerodynamic coefficients for same Mach number can be different at different altitude due to difference in Reynolds number. Prediction of these aerodynamics coefficients can be made through experiments, analytical solution or Computational Fluid Dynamics (CFD). Advancements in computational power have generated the concept of using CFD as a virtual Wind Tunnel (WT), hence aerodynamic performance prediction in present study is based upon CFD (numerical test rig). Simulations at different altitudes for a range of Mach numbers with zero angle of attack are performed to predict axial force coefficient behavior with altitude (Reynolds number). Similar simulations for a fixed Mach number ‘3’ and a range of angle of attacks are also carried out to envisage the variation in normal force and pitching moment coefficients with altitude (Reynolds number). Results clearly depict that the axial force coefficient is a function of altitude (Reynolds number) and increase as altitude increases, especially for subsonic region. Variation in axial force coefficient with altitude (Reynolds number) slightly increases for larger values of angle of attacks. Normal force and pitching moment coefficients do not depend on altitude (Reynolds number) at smaller values of angle of attacks but show slight decrease as altitude increases. Present study suggests that variation of normal force and pitching moment coefficients with altitude can be neglected but the variation of axial force coefficient with altitude should be considered for vehicle fly in dense atmosphere. It is recommended to continue this study to more complex configurations for various Mach numbers with side slip and real gas effects.
Pub.: 22 Mar '17, Pinned: 12 Apr '17
Effect of Static Shape Deformation on Aerodynamics and Aerothermodynamics of Hypersonic Inflatable Aerodynamic Decelerator
Abstract: The inflatable aerodynamic decelerator (IAD), which allows heavier and larger payloads and offers flexibility in landing site selection at higher altitudes, possesses potential superiority in next generation space transport system. However, due to the flexibilities of material and structure assembly, IAD inevitably experiences surface deformation during atmospheric entry, which in turn alters the flowfield around the vehicle and leads to the variations of aerodynamics and aerothermodynamics. In the current study, the effect of the static shape deformation on the hypersonic aerodynamics and aerothermodynamics of a stacked tori Hypersonic Inflatable Aerodynamic Decelerator (HIAD) is demonstrated and analyzed in detail by solving compressible Navier-Stokes equations with Menter's shear stress transport (SST) turbulence model. The deformed shape is obtained by structural modeling in the presence of maximum aerodynamic pressure during entry. The numerical results show that the undulating shape deformation makes significant difference to flow structure. In particular, the more curved outboard forebody surface results in local flow separations and reattachments in valleys, which consequently yields remarkable fluctuations of surface conditions with pressure rising in valleys yet dropping on crests while shear stress and heat flux falling in valleys yet rising on crests. Accordingly, compared with the initial (undeformed) shape, the corresponding differences of surface conditions get more striking outboard, with maximum augmentations of 379 pa, 2224 pa, and 19.0 W/cm2, i.e., 9.8%, 305.9%, and 101.6% for the pressure, shear stress and heat flux respectively. Moreover, it is found that, with the increase of angle of attack, the aerodynamic characters and surface heating vary and the aeroheating disparities are evident between the deformed and initial shape. For the deformable HIAD model investigated in this study, the more intense surface conditions and changed flight aerodynamics are revealed, which is critical for the selection of structure material and design of flight control system.
Pub.: 23 Mar '17, Pinned: 12 Apr '17
Aeroelastic simulation of the wind-excited torsional vibration of a parabolic trough solar collector
Abstract: We investigate the wind-excited torsional vibration of a parabolic trough solar collector using large eddy simulation. Past studies of wind loads on parabolic trough solar collectors have used rigid models, thereby neglecting possible feedback effects of structural motion on wind loads. Therefore, the primary aim of this study is to assess the extent to which feedback effects of the structural motion on aerodynamic loading can affect the response. To this end, we perform both one-way and two-way coupled fluid-structure interaction simulations corresponding to rigid and aeroelastic models, respectively. In both cases, the collector is exposed to realistic time-varying wind gusts in order to account for their effect on the flow instabilities around the structure. Comprehensive data obtained by numerical simulation is analyzed to provide new insight into the transient flow behavior around a collector and its interaction with the torsional vibration. We show that significant self-excited vibrations can occur for certain pitch angles. The onset of self-excited vibrations coincides with the synchronization of the vortex shedding process with the torsional vibration of the collector.
Pub.: 18 Mar '17, Pinned: 12 Apr '17
Fluctuating wind pressure distribution around full-scale cooling towers
Abstract: At present, external wind pressure description around cooling towers in various loading Codes is based on full-scale measurement data. The data has been collected during 1960s–1990s for hyperbolic cooling towers with heights of about 90 m~120 m, and focus has been usually on the average wind pressure distribution. In fact, modern cooling towers taller than 165 m show sensitivity to wind-induced effects under strong wind excitation. The performance of these flexible structures is closely related to the fluctuating wind action in the atmospheric boundary layer. Modeling of these features is underscored by the difficulty in matching supercritical Reynolds number in boundary layer wind tunnels. Accordingly, it has been difficult to accurately establish a relationship between fluctuating pressures on the surface of a cooling tower to inflow conditions. This has caused a bottleneck for enhancements in the state of wind resistant structural design of larger cooling towers. In view of this difficulty, high Reynolds number flows were simulated in the wind tunnel using scaled model with a combination of surface roughness elements to establish a relationship between the inflow turbulence intensity and pressure fluctuations. This was supplemented by a validation using data from long-term measurements of wind pressure around a 166.68 m cooling tower. Wind tunnel experiments were in a general agreement with full-scale observations which offered a relationship between the fluctuating wind pressure distribution and the incoming turbulence intensity at supercritical Reynolds number conditions (Re≥4×10E7).
Pub.: 06 Mar '17, Pinned: 12 Apr '17