The unsteady flow past a NACA 0012 airfoil that is undertaking a constant-rate pitching up motion is investigated experimentally by the PIDV technique in a water towing tank. The Reynolds number is 5000, based upon the airfoil's chord and the free-stream velocity. The airfoil is pitching impulsively from 0 to 30 deg. with a dimensionless pitch rate alpha of 0.131. Instantaneous velocity and associated vorticity data have been acquired over the entire flow field. The primary vortex dominates the flow behavior after it separates from the leading edge of the airfoil. Complete stall emerges after this vortex detaches from the airfoil and triggers the shedding of a counter-rotating vortex near the trailing edge. A parallel computational study using the discrete vortex, random walk approximation has also been conducted. In general, the computational results agree very well with the experiment.

Unsteady flow past an airfoil pitching at a constant rate

An immersed interface method for the Vortex-In-Cell algorithm

Prediction of unsteady flow around square and rectangular section cylinders using a discrete vortex method

Trailing-edge-flap flow control for the mitigation of large negative pitching moments and negative aerodynamic damping caused by helicopter rotor blade dynamic stall was studied by means of computational fluid dynamics. A discrete vortex method was used for the simulations. The model geometry was a NACA 0012 airfoil oscillating in an α(t) = 15 deg + 10 deg sin(ωt) motion at the reduced frequency of k = 0.173. The freestream flow conditions were of M = 0.117 and Re = 1.463296 x 10 6 . The flap actuation was a brief pulse signal of a sinusoidal shape

Alleviation of airfoil dynamic stall moments via trailing-edge-flap flow control

The paper presents a two-dimensional immersed interface technique for the vortex-in-cell (VIC) method for the simulation of flows past complex geometries. The particle-mesh VIC algorithm is augmented by a local particle-particle (PP) correction term in a particle-particle particle-mesh (PPPM) context to resolve sub-grid scales incurred by the presence of the immersed interface. The PP correction furthermore allows mesh and particle resolution to be disjoined by explicitly resolving sub-grid scales on the particles. This PPPM algorithm uses an influence matrix technique to annihilate the anisotropic sub-grid scales and an exact PP correction term. Free-space boundary conditions are satisfied through the use of modified Green's functions in the solution of the Poisson equation for the stream function. The random walk technique is employed for the diffusion in order to relax the need for a remeshing of the computational elements close to solid boundaries. The immersed interface technique is applied to the fl...

An immersed interface method for the vortex-in-cell algorithm

Amodi® ed discrete vortexmethod to simulate the separated ow around an aerofoil undergoingpitchingmotion is described The vorticity generated in the thin layer around the body is discretized into vortices in accordance with themultipanel surface representation By convectionand diffusion the vortices are released from the body and advanced in the wake as determined by the Biot± Savart law and random-walkmodel, respectively Both unsteady static and pitching cases are presented, and comparisonwith the test data illustrates that, without prior knowledge of the developing separation and reattachment points for the model, good agreement has been achieved

Discrete Vortex Method for Simulating Unsteady Flow

Amodi® ed discretevortex method to simulatetheseparatedowaround an aerofoil undergoing pitching motion is described. The vorticity generated in the thin layer around the body is discretized into vortices in accordance withthemultipanel surfacerepresentation. Byconvectionand diffusionthevorticesarereleased fromthebody and advanced in the wake as determined by the Biot± Savart law and random-walk model, respectively. Both unsteady static and pitching casesare presented, and comparison with the test data illustratesthat, without priorknowledge of the developing separation and reattachment points for the model, good agreement has been achieved. Nomenclature A = area of body (section) B = volume within the body c = aerofoil chord Fb = volume within the control zone Fw = volume outside the control zone K = number of subpanels for each panel k = unit vector k = reduced pitch rate k = X c/2V l = panel length m = index number of subpanel within the panel N = number of panels for the body P = static pressure Re = Reynolds number r, r = position vector and its magnitude S = surface of the body s, n = unit vector along and normal to the surface t = time U = ¯ ow velocity V = velocity Z = position in the form of complex number z = vortex position in the form of complex number a = angle of attack C = circulation c = circulation density 4 t = time step d = distance of nascent vortex off the body m = kinematic viscosity q = ¯ uid density r = vortex core radius W ,W = vector potential and stream function X = rotational velocity x = vorticity Subscripts

Hequan Lin

Papers

Discrete Vortex Method for Simulating Unsteady Flow

Discrete Vortex Method for Simulating Unsteady Flow Around Pitching Aerofoils