CFD Validation of the Optimal Arrangement of the Propulsive Dorsal Fin of Gymnarchus niloticus

Gymnarchus niloticus, a typical freshwater fish, swims by undulations of a long-based dorsal fin aided by the two pectoral fins, while commonly it holds its body rigid and straight. The long flexible dorsal fin is the main propulsor of G niloticus; it has also considerable influence on the streamline profile. This paper proposes a CFD approach to validate that the natural arrangement of the propulsive dorsal fin is optimal. Using morphological data and a smoothness-keeping algorithm, the dorsal fin is ‘virtually＇ moved forward and backward with several displacements from the natural location. For each case, we reconstruct geometry, generate CFD grids, and calculate the pressure, viscous and total drag coefficients respectively. The results show that the pressure and total drag coefficients increase whether the dorsal fin is displaced forward or backward, and that greater displacement from its original position leads to greater pressure and total drag coefficients. This suggests that the natural position of the dorsal fin is significant for maintaining the fish＇s streamline profile and reducing drag.

New CFD Validation Method with Application to Verify Computations of Near Wall Flows

For high Re number flows,a new computational fluid dynamics （CFD） validation method,namely,wall-surface compatibility criteria method and also called Gao＇s criteria,is proposed to verify near wall flows.As examples,Gao＇s criteria method and other two CFD verification methods （analytic solutions method and grid convergence analysis） are used to verify FLUENT＇s near wall flows solutions for two-dimensional incompressible laminar stagnation-point flows.The exact solution of the Navier-Stokes equations for laminar stagnation-point flows satisfy accurately all Gao＇s criteria,numerical simulations of laminar stagnation-point flows show that when physical parameters （the pressure coefficient and the Stanton number at wall surface） achieve convergence with more and more fine-screen grid,a part of Gao＇s criteria are not satisfied.

ON DISPERSION-CONTROLLED PRINCIPLES FOR NON-OSCILLATORY SHOCK-CAPTURING SCHEMES

The role of dispersions in the numerical solutions of hydrodynamic equation systems has been realized for long time.It is only during the last two decades that extensive studies on the dispersion-controlled dissipative(DCD)schemes were reported.The studies have demonstrated that this kind of the schemes is distinct from conventional dissipation-based schemes in which the dispersion term of the modified equation is not considered in scheme construction to avoid nonphysical oscillation occurring in shock wave simulations.The principle of the dispersion controlled aims at removing nonphysical oscillations by making use of dispersion characteristics instead of adding artificial viscosity to dissipate the oscillation as the conventional schemes do.Research progresses on the dispersion- controlled principles are reviewed in this paper,including the exploration of the role of dispersions in numerical simulations,the development of the dispersion-controlled principles,efforts devoted to high-order dispersion-controlled dissipative schemes,the extension to both the finite volume and the finite element methods,scheme verification and solution validation,and comments on several aspects of the schemes from author's viewpoint.

Experimental Investigation of the Aerodynamic Flow in the Aircraft Carrier Ski-jump by means of PIV

Computational Fluid Dynamics （CFD） methods have opened a new field to perform aerodynamic studies saving money and time. The difficulties presented by this method to calculate complex flow field problems imply that CFD validation is needed to provide correct results. Experimental data have recently been used to validate the accuracy of CFD predictions. Particle Image Velocimetry （PIV） has shown to be a powerful tool in the investigation of complex flows. The aim of this paper is to present results from PIV experiments that would be interesting for CFD validation. Regarding aircraft operations, the short runway available implies the necessity of equipment which helps to take-off performances. Ski-jump ramp system improves aircraft performances by an increment of lift resulting in successful take-off operations. The ski-jump ramp presence generates a complex flow bounded by a turbulent shear layer and a low velocity recirculation bubble over the end of the flight deck. The adverse effects on the aircraft aerodynamics affect to pilot safe operations, so this region is an interesting problem to be studied by means of wind tunnel experimental tests.

Recent development of a CFD-wind tunnel correlation study based on CAE-AVM investigation

This paper starts with brief introduction to the open topic of the CFD and wing tunnel correlation study, followed by a description of the Chinese Aeronautical Establishment（CAE） –Aerodynamic Validation Model（AVM） and its wind tunnel test in the German-Dutch Wind tunnels（DNW）. The features of the aerodynamic design, the CFD approach, the wind tunnel model fabrication and the experimental techniques are discussed along with the motivation of the CAEDNW workshop on CFD-wind tunnel correlation study. The workshop objective is focused on the interference from the aero-elastic deformation of the wind tunnel model and the model support system to the aerodynamic performance and CFD validations. The four study cases, geometry and mesh preparation of the workshop are introduced. A comprehensive summary of the CFD results from the organizer and the participants is provided. Major observations, both CFD to CFD and CFD to wind tunnel, are identified and summarized. The CFD results of the participants are in good agreement with each other, and with the wind tunnel test data when the wing deformation and a Z-sting system are included in the CFD, indicating the importance of considering such interference at high subsonic Mach number of 0.85.

Transition Modelling Implications in the CFD Analysis of a Turbine Nozzle Vane Cascade Tested Over a Range of Mach and Reynolds Numbers

The aerodynamic performance of a gas turbine nozzle vane cascade was investigated over a range of Mach and Reynolds numbers.The work is part of a vast research project aimed at the analysis of fluid dynamics and heat transfer phenomena in cooled blades.In this paper computed results on the"solid vane"(without cooling devices)are presented and discussed in comparison with experimental data.Detailed measurements were provided by the University of Bergamo where the experimental campaign was carried out by means of a subsonic wind tunnel.The impact of boundary layer transition is investigated by using a novel laminar kinetic energy transport model and the widely used Langtry-Menterγ-Reθ,t model.The comparison between calculations and measurements is presented in terms of blade loading distributions,total pressure loss coefficient contours downstream of the cascade,and velocity/turbulence-intensity profiles within the boundary layer at selected blade surface locations at mid-span.It will be shown how transitional calculations compare favorably with experiments.