Radiation and control of sound from evolving wave packet on a concave-convex surface
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Maestrello, Lucio↗
Engineering topics
Maestrello, Lucio
Publications and source records attributed to Maestrello, Lucio.
Application of localized surface heating to actively control the boundary layer separation
The use of localized surface heating to improve the performance of the airfoil of a fixed wing or rotating blade at high angle of attack is considered. Separation control by active means can be accomplished by acoustic perturbation of the separated area above the airfoil or by localized surface heating in a pressure gradient region. Active control by sound in the vicinity of the leading edge of an airfoil is shown to greatly reduce the area of separation. Therefore, the overall circulation is sufficiently changed to result in an increase in lift and a reduction in drag.
El-Hady, Nabit M.↗
Transition delay and relaminarization of turbulent flow
Several techniques used for delaying transition both in air and water are overviewed, among them uniform surface heating, localized surface heating, and the application of broad-band disturbance-wave cancellation using the wave superposition principle. It is pointed out that localized heating, in air, can effectively delay transition along a flat plate and reduce viscous drag. Attention is focused on an experiment where the feasibility of relaminarizing turbulent flow over a flat plate with an upstream concave-convex curvature, in air, has been demonstrated using localized heating on the concave part of the curved surface. The flow over the curved surface investigated by thermal mapping using an infrared technique is also covered.
Maestrello, Lucio↗
Numerical Study of Three-dimensional Spatial Instability of a Supersonic Flat Plate Boundary Layer
The behavior of spatially growing three-dimensional waves in a supersonic boundary layer was studied numerically by solving the complete Navier-Stokes equations. Satisfactory comparison with linear parallel and non-parallel stability theories, and experiment are obtained when a small amplitude inflow disturbance is used. The three-dimensional unsteady Navier-Stokes equations are solved by a finite difference method which is fourth-order and second-order accurate in the convection and viscous terms respectively, and second-order accurate in time. Spanwise periodicity is assumed. The inflow disturbance is composed of eigenfunctions from linear stability theory. By increasing the amplitude of the inflow disturbance, nonlinear effects in the form of a relaxation type oscillation of the time signal of rho(u) are observed.
Maestrello, Lucio↗
Control of sound radiation from a wavepacket over a curved surface
Active control of acoustic pressure in the far field resulting from the growth and decay of a wavepacket convecting in a boundary layer over a concave-convex surface is investigated numerically using direct computations of the Navier-Stokes equations. The resulting sound radiation is computed using linearized Euler equations with the pressure from the Navier-Stokes solution as a time-dependent boundary condition. The acoustic far field exhibits directivity type of behavior that points upstream to the flow direction. A fixed control algorithm is used where the attenuation signal is synthesized by a filter which actively adapt it to the amplitude-time response of the outgoing acoustic wave.
Maestrello, Lucio↗
Relaminarization of turbulent flow on a flat plate by localized surface heating
Relaminarization of a turbulent boundary layer in air on a flat plate is demonstrated experimentally using localized surface heating. Localized heating is achieved by electrically heating a wire embedded in a thermally insulated substrate (Space Shuttle Tile) on the surface. The stability of the flow downstream of the applied control point increases with decreasing stream temperature in the flow direction. The mean and perturbation velocity profiles without control show that the flow is turbulent. With control, these profiles sequentially change from intermittently turbulent to a fully laminar state. In the relaminarization stage, the turbulent energy is dissipated by molecular transport due to viscous and conductivity mechanisms. The new profile adjusts to a lower Reynolds number based on the momentum thickness than that of the previous turbulent state.
Maestrello, Lucio↗
An application of active surface heating for augmenting lift and reducing drag of an airfoil
Application of active control to separated flow on the RC(6)-08 airfoil at high angle of attack by localized surface heating is numerically simulated by integrating the compressible 2-D nonlinear Navier-Stokes equation solver. Active control is simulated by local modification of the temperature boundary condition over a narrow strip of the upper surface of the airfoil. Both mean and perturbed profiles are favorably altered when excited with the same natural frequency of the shear layer by moderate surface heating for both laminar and turbulent separation. The shear layer is found to be very sensitive to localized surface heating in the vicinity of the separation point. The excitation field at the surface sufficiently altered both the local as well as the global circulation to cause a significant increase in lift and reduction in drag.
Maestrello, Lucio↗
Control of the boundary layer separation about an airfoil by active surface heating
Application of active control to separated flow on the RC(6)-08 airfoil at high angle of attack by localized surface heating is numerically simulated by integrating the compressible two-dimensional nonlinear Navier-Stokes equations solver. Active control is simulated by local modification of the temperature boundary condition over a narrow strip on the upper surface of the airfoil. Both mean and perturbed profiles are favorably altered when excited with the same natural frequency of the shear layer by moderate surface heating for both laminar and turbulent separation. The shear layer is found to be very sensitive to localized surface heating in the vicinity of the separation point. The excitation field at the surface sufficiently altered both the local as well as the global circulation to cause a significant increase in lift and reduction in drag.
Maestrello, Lucio↗
Application of sound and temperature to control boundary-layer transition
The growth and decay of a wave packet convecting in a boundary layer over a concave-convex surface and its active control by localized surface heating are studied numerically using direct computations of the Navier-Stokes equations. The resulting sound radiations are computed using linearized Euler equations with the pressure from the Navier-Stokes solution as a time-dependent boundary condition. It is shown that on the concave portion the amplitude of the wave packet increases and its bandwidth broadens while on the convex portion some of the components in the packet are stabilized. The pressure field decays exponentially away from the surface and then algebraically, exhibiting a decay characteristic of acoustic waves in two dimensions. The far-field acoustic behavior exhibits a super-directivity type of behavior with a beaming downstream. Active control by surface heating is shown to reduce the growth of the wave packet but have little effect on acoustic far field behavior for the cases considered. Active control by sound emanating from the surface of an airfoil in the vicinity of the leading edge is experimentally investigated. The purpose is to control the separated region at high angles of attack. The results show that injection of sound at shedding frequency of the flow is effective in an increase of lift and reduction of drag.
Maestrello, Lucio↗
Active Control of Transition and Turbulence
Two active means of manipulating boundary-layer flow developed, one controlling laminar-to-turbulent transition, other controlling amplitude of turbulent fluctuation. Purpose to control skin-friction drag over surfaces inside inlets and ducts. Resulting turbulence downstream has lower skin-friction drag than equivalent flow developing over same surfaces in absence of intervention. Heating strips trigger turbulence while transition amplitude and bandwidth controlled by acoustic signal.
Maestrello, Lucio↗
Study of instability and active control of boundary layers using Navier-Stokes equations
Spatial stability of a three-dimensional growing boundary layer is studied using Navier-Stokes equations. The finite difference method used is an explicit, predictor-corrector type which is fourth-order accurate in space and second-order in time. Active control of two-dimensional disturbances is simulated by localized surface heating. The computations show features of the flow relevant to early stages of transition such as lifting of vorticity away from the wall and localized regions of intense shear. Active control with single heating strip is only marginally effective, but may be improved by multiple strips.
Parikh, Paresh↗