Flow around circular and noncircular cylinders by a low-order panel method

SummaryThree low-order panel methods developed for the analysis of supersonic flows have been used to make calculations for a number of test configurations, with the aim of establishing the range of problems for which this class of computational method yields adequate solutions. The programs investigated were the Woodward USSAERO/C program, the related NLRAERO program, and the British Aerospace Warton supersonic panel program. Results obtained using these programs have been evaluated against theoretical and experimental data for a number of test cases covering wing-alone, body-alone and wing-body geometries. It is concluded that low-order panel methods can provide adequate solutions for supersonic flows about wings, bodies and wing-body combinations, provided the assumptions implicit in the linearised potential flow model are not violated. Examples show that the prediction of lift and pitching moment curve slopes for quite complex configurations may be acceptable, but that the detailed pressure distributions are not always predicted satisfactorily. In particular, serious problems are encountered in calculating the flow about wings with rounded supersonic leading edges due to the linearised flow model which is used.

A zonal method based on the iterative coupling between an in viscid panel method and a Navier-Stokes (NS) method has been developed to analyze the complex flowfield associated with the V/STOL flow environment in order to improve the prediction of aerodynamic characteristics. The low-order panel method, VSAERO, developed by Analytical Methods, Inc. is used to solve for the entire flow region, which includes the V/STOL configuration and jet boundary model. In two separate investigations presented here, ARC3D, a well-known compressible thin layer NS code developed at NASA Ames Research Center, and APPL, a parabolized NS code developed at Amtec Engineering, are used to solve for the details of the jet region subject to the boundary condition provided by VSAERO. Overlapping boundaries are used for the purpose of coupling. Comparisons with the available experimental data for a jet-in-crossflow and a V/STOL configuration with lift-jet in a subsonic freestream show qualitative agreement with experiment and improved correlations over those by inviscid computations alone.

Flow-induced vibrations (FIV) can occur when a flexible or flexibly mounted bluff body is exposed to fluid flow. As the flow passes the structure, the shed vortices downstream of the body can produce fluctuating forces on the structure, causing large-amplitude oscillations. FIV is known as a destructive phenomenon causing fatigue damage to engineering structures. Over the past few decades, numerous studies have been conducted on the FIV of a circular cylinder as a canonical geometry. The FIV response of a bluff body is highly sensitive to its cross-sectional geometry as the location of the separation point, which is intricately linked to the vortex-shedding mechanism, is different for each geometry. Previous studies on the FIV of structures with non-circular and asymmetric cross-sections have mainly focused on the flexibly-mounted rigid bodies in flow. However, to fully understand the complex dynamic response of the system in many real-life applications where the structure has a non-circular cross-section, such as iced-covered electrical transmission lines, decks of suspension bridges, tension chains, and the riser that become asymmetric due to corrosion in the water, the structure’s spanwise flexibility should be considered. This research attempts to fill the gap in the literature by doing laboratory measurements to investigate the FIV of flexible bluff bodies with an asymmetric and non-circular cross-section. The two structures studied in this research are (a) a flexible cylinder with a triangular cross-section and (b) a flexible circular cylinder with an attached flexible splitter plate. Among the parameters affecting the FIV response of the system, the role of the angle of attack of the triangular cylinder and the length of the splitter plate is investigated in our study. Findings from this research can leverage our fundamental understanding of the fluid-structure interactions response of the long-span flexible asymmetric structures, with applications in the design of fluidic energy harvesters as well as suppression of unwanted vibrations of systems operating in fluid environments. A series of well-controlled lab experiments have been conducted using water channel tests. Cylinder’s oscillation was captured using a high-speed imaging technique, and the spanwise continuous response was reconstructed using a modal-analysis based technique. The structural response of the system is analyzed in terms of its oscillation amplitude and frequency. Qualitative and quantitative flow field visualizations and measurements have been conducted using Hydrogen Bubble (HB) and the state-of-the-art time-resolved volumetric Particle Tracking Velocimetry(TR-PTV) techniques. Three-dimensional vortex dynamics in the wake of the structure are studied and analyzed using the proper orthogonal decomposition technique. The interaction between structural dynamic response and the vortex-dominated flow field in the wake of the structure leads to a fully coupled fluid-structure interactions response that is investigated in this research.

A closed form for low-order panel methods

A BEM-isogeometric method for the ship wave-resistance problem

The local error of a low-order boundary element method at the trailing edge of a hydrofoil and its effect on the global solution

The added mass coefficients for two and three-dimensional submerged bodies were calculated using a low-order panel code. The source and dipole strengths, and the panel surface area for each panel, were used to compute the integrals needed for added mass in all six degrees of motions. Several applications of this method were used in comparing the results with the theoretical, when available, experimental or other numerical results. The method was found to be successful in predicting the added mass coefficients using relatively low numbers of panels.

Aerodynamic characteristics of a guided rocket projectile are numerically simulated. Simulations are performed in a range of flight conditions using a commercial CFD software FLUENT, and variations of lift coefficients and drag coefficients with Mach numbers and angles of attack were demonstrated. The numerical results also indicate that the angle of canard deflection has significant influence on the flow field near tailfins.

A suitable low order panel method is introduced, that allows the calculation of free vortex sheets emanating from sharp-edged wings in subsonic flow. The wing surfaces as well as the separated shear layers are discretized into panels, each carrying a constant doublet distribution. Bodies — e.g. fuselages — can be modeled by a network of source panels with elementwise constant strength.

A computerized analysis of supersonic nonuniform flows over sharp and spherically blunted cones at angle of attack

As the interest in arctic shipping and arctic exploration of oil and gas is increasing in recent years, the number of ice class vessels is increasing rapidly. Also the choices for propulsion devices are getting wider and these include podded propulsion systems. This study is a framework for the numerical prediction of the ice interaction loads acting on a podded propeller blade. The results of this study will help us to understand the propeller-ice interaction problem more comprehensively. Several studies for propeller-ice interaction have been carried out in the past few decades. Propeller-ice interaction, however, is a complicated process with a high level of uncertainties due to ice properties, ship operating conditions, and environmental conditions. Full-scale measurements involve high costs. In order to overcome these difficulties, model tests were carried out with model ice in an ice tank. The model tests provide well-controlled ice properties and interaction conditions to reduce the uncertainties. The tests were carried out in the ice tank with scaled down model ice at the National Research Council of Canada’s Institute for Ocean Technology. The ice loads acting on the propeller blade were measured with a six-component force and moment load cell fitted to the shaft and one of the propeller blades. Based on the experimental results, a numerical prediction model was developed to estimate the ice loads on the propeller blade. The numerical prediction is composed of three parts: the hydrodynamic calculations including separable and inseparable hydrodynamic loads, and the ice milling loads calculation. The separable and inseparable hydrodynamic loads can be obtained from clear water and blocked flow respectively. The hydrodynamic calculations were done by a low order panel method. The subroutines for calculating the ice milling loads are implemented into the panel method. The numerical prediction model for ice milling loads is described and the results are compared with those of experiments.

A novel method of calculating static derivatives and acceleration derivatives using Computational Fluid Dynamics is presented. This method uses field velocity approach to simulate the unsteady forced-plunging flow field over the aircraft without updating the field grids during each time step. This provides an improvement in computational efficiency over similar precision without loss of generality. Finally, to verify the present method, the Basic Finner missile as the benchmark example was taken to calculate its acceleration derivatives at various Mach number. Results are in fairly good agreement with traditionally method and the tunnel experimental results. Comparisons with the results of time-dependent simulations are also included.

Evolution of disturbances in three-dimensional boundary layers

Corrugations are folds on a surface as found on wings of dragon fly insects. Although they fly at relatively lower altitudes its wings are adapted for better aerodynamic and aero-elastic characteristics. In the present work, three airfoil geometries were studied using the 2-D panel method to evaluate the aerodynamic performance for low Reynolds number. The experiments were conducted in wind tunnel for incompressible flow regime to demonstrate the coefficients of lift drag and glide ratio at two Reynolds numbers 1.9x104 and 1.5x105 and for angles of attack ranging between 00 and 160. The panel method results have been validated using the current and existing experiment data as well as with the computational work from cited literature. A good agreement between the experimental and the panel methods were found for low angles of attack. The results showed that till 80 angle of attack higher lift coefficient and lower drag coefficient are obtainable for corrugated airfoils as compared to NACA 0010. The validation of surface pressure coefficients for all three airfoils using the panel method at 40 angles of attack was done. The contours of the non-dimensional pressure and velocity are illustrated from -100 to 200 angles of attack. A good correlation between the experiment data and the computational methods revealed that the corrugated airfoils exhibit better aerodynamic performance than NACA 0010.

Steady and unsteady asymmetric vortical flows around slender bodies at high angles of attack are solved using the unsteady, compressible, this-layer Navier-Stokes equations. An implicit, upwind-biased, flux-difference splitting, finite-volume scheme is used for the numerical computations. For supersonic flows past point cones, the locally conical flow assumption has been used for efficient computational studies of this phenomenon. Asymmetric flows past a 5° semiapex-angle circular cone at different angles of attack, free-stream Mach numbers, and Reynolds numbers has been studied in responses to different sources of disturbances. The effects of grid fineness and computational domain size have also been investigated. Next, the responses of three-dimensional supersonic asymmetric flow around a 5° circular cone at different angles of attack and Reynolds numbers to short-duration sideslip disturbances are presented. The results show that flow asymmetry becomes stronger as the Reynolds number and angles of attack are increased. The asymmetric solutions show spatial vortex shedding which is qualitatively similar to the temporal vortex shedding of the unsteady locally conical flow. A cylindrical afterbody is also added to the same cone to study the effect of a cylindrical part on the flow asymmetry. One of the cases of flow over a cone-cylinder configuration is validated fairly well by experimental data.