Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session BO: Turbulence: Control I |
Hide Abstracts |
Chair: Barton Smith, Utah State University Room: Salt Palace Convention Center 251 C |
Sunday, November 18, 2007 10:34AM - 10:47AM |
BO.00001: Combining Countercurrent Shear Flow Control and Transverse Jets for Fluidic Thrust Vector Control Ignacio Echavarria Diaz-Guardamino, David Forliti Countercurrent shear flow control has been established as an effective method for thrust vector control but has been challenged by hardware integration issues. Recent developments in fluidic thrust vector control have focused on nozzle interior methods that skew the throat of the nozzle using multiple transverse jets. The present work is motivated to combine these two flow control approaches to create a thrust vector control technique with enhanced performance. A combined computational and experimental effort was undertaken to consider the integration of these two flow control techniques. A simple configuration of a channel flow was used with consideration of various geometrical and operating conditions. It is apparent that the employment of countercurrent flow control does enhance the thrust vector control performance over a single transverse jet. The influence of countercurrent shear on the turbulence created with the transverse jet will be studied to help understand how the two flow control methodologies contribute to the pressure gradients required for thrust vectoring. [Preview Abstract] |
Sunday, November 18, 2007 10:47AM - 11:00AM |
BO.00002: Three methods for Aerodynamically Vectoring a Planar Jet With Steady Control Flows Brandon Wilson, Ben Timmins, Barton Smith An experimental demonstration of Aerodynamic Jet Vectoring and its optimization for efficiency and stability is presented. Aerodynamic jet vectoring is an important element in new technologies for non-contact particle-size characterization, and particle detection for air quality testing. Aerodynamic jet vectoring used either a single, small, steady, suction or blowing control flow or a combination of both to redirect a two dimensional primary jet from its original path. For blowing only, three parameters are defined which influence the stability and vectoring efficiency of the vectored fluid stream. These are angle of the blowing flow with respect to the primary jet, the height of the blowing flow above the primary jet, and exit cross sectional area of the blowing flow. Vectoring efficiency is defined as the ratio of the momentum flux of the blowing to the primary jet. Alternately, it will be shown that similar vectoring can be achieved with suction control only, or with combinations of suction and blowing. Use of both suction and blowing results in much larger vectoring efficiencies, but can result in adverse flow field fluctuations. [Preview Abstract] |
Sunday, November 18, 2007 11:00AM - 11:13AM |
BO.00003: Control of High-Speed Spray Flows Using a Steady, Parallel Control Flow Under the Influence of the Coanda Effect Dustin Allen, Barton Smith An experimental demonstration of a jet vectoring technique used in our novel spray device called a Coanda-assisted Spray Manipulation (CSM) nozzle is presented. The CSM makes use of a Coanda-like effect on axisymmetric geometries through the interaction of a high volume-flow primary jet flowing through the center of a collar and a secondary high-momentum jet parallel to the first and adjacent to a convex collar. The control jet attaches to the convex wall and vectors due to the Coanda effect, entraining and vectoring the primary jet, resulting in controllable r-theta directional spraying. Various annular secondary exit holes and curved wall radii were tested over a range of momentum flux ratios to study the effects of these variables on the vectored jet angle. Particle Image Velocimetry (PIV) was used to determine the vectoring angle and the profile of the primary jet in each experiment. The experiments show that the secondary exit hole size and curve wall radius, along with the momentum ratios of the two jets predominantly affect the vectoring angle of the primary jet. Also, the jet profile is largely unchanged with vectoring for high velocity flows, which is important for the thermal spray applications for which CSM will be used. [Preview Abstract] |
Sunday, November 18, 2007 11:13AM - 11:26AM |
BO.00004: Turbulent Boundary Layer Control using Plasma Actuators David M. Schatzman, Flint O. Thomas This experimental study is focused on turbulent boundary layer flow control using single dielectric barrier discharge plasma actuators. PIV measurements are used to document the effect of plasma actuation on the turbulent boundary layer flow. Flow control experiments were conducted for both a flat plate zero pressure gradient turbulent boundary layer flow and an adverse pressure gradient boundary layer over a convex ramp section. The effect of plasma actuation is characterized by the momentum addition to the near wall region shown in the boundary layer profiles extracted at various locations downstream of actuation. Measurements are presented which allow one to discern the physical mechanisms associated with both steady and unsteady plasma actuation. [Preview Abstract] |
Sunday, November 18, 2007 11:26AM - 11:39AM |
BO.00005: Cylinder Flow Control Using Plasma Actuators Alexey Kozlov, Flint Thomas In this study the results of flow control experiments utilizing single dielectric barrier discharge plasma actuators to control flow separation and unsteady vortex shedding from a circular cylinder in cross-flow are reported. Two optimized quartz dielectric plasma actuators mounted on the cylinder surface utilizing an improved saw-tooth waveform high-voltage generator allowed flow control at Reynolds number approaching supercritical. Using either steady or unsteady actuation, it is demonstrated that the plasma-induced surface blowing gives rise to a local Coanda effect that promotes the maintenance of flow attachment. PIV based flow fields and wake velocity profiles obtained with hot-wire anemometry show large reductions in vortex shedding, wake width and turbulence intensity. [Preview Abstract] |
Sunday, November 18, 2007 11:39AM - 11:52AM |
BO.00006: Simulation of SDBD Plasma Actuators on Arbitrarily Shaped Surfaces Benjamin Mertz, Thomas Corke, Mehul Patel The results from the simulation of a Single Dielectric Barrier Discharge (SDBD) based ``plasma actuator'' on an arbitrarily shaped surface are presented. The actuators are made up of two electrodes separated by a dielectric barrier. By applying a high voltage a.c. signal to the electrodes, the air ionizes around the regions of largest electric potential. The asymmetric placement of the electrodes produces an electric field gradient which will impose a body force vector field on the ionized air which can be used for flow control applications. The simulation of the actuator uses a lumped-circuit model, which simulates the plasma formation at the a.c. time scales, to provide the unsteady boundary conditions for the solution of the governing electrostatic equations. The electrostatic equations are solved at each time step in a generalized coordinate system using a second order central difference approximation for the spacial derivatives. The body force is then calculated and time-averaged to produce a force field which can be used in flow simulations. Simulations involving plasma actuator control of turbulent separated flows for different surface geometries are then presented. [Preview Abstract] |
Sunday, November 18, 2007 11:52AM - 12:05PM |
BO.00007: Experiment and Simulation of Turbulent Separation Control over a Hump Model using Plasma Actuator Chuan He, Thomas Corke, Mehul Patel This work presents the development of plasma flow control of a turbulent boundary layer separation over a hump model used in NASA Langley Workshop on CFD Validation of Synthetic Jets and Turbulent Separation control. Two arrangements of the plasma actuator were studied experimentally: one to produce spanwise vortices for reattaching the flow, and the other that was designed to produce counter-rotating streamwise vortices. The results show that the plasma actuator was effective in turbulent boundary layer separation control. In the simulation, the Reynolds-averaged Navier-Stokes equations with k-$\epsilon$, SA and k-$\omega$ turbulence models and our SDBD plasma actuator body force model were solved using Fluent to predict the flow separation and reattachment locations, and its control by the plasma actuator. This was done for the same configurations and flow conditions as the experiment so that direct comparisons could be made. The results showed excellent agreement between the simulations and the experiments. This is primarily a validation of the SDBD plasma actuator modelling which can then be used in the design of plasma flow control systems in other flow geometries. [Preview Abstract] |
Sunday, November 18, 2007 12:05PM - 12:18PM |
BO.00008: Control of Separated Turbulent Flow over a Hump using RANS, DES, and LES Subhadeep Gan, Urmila Ghia, Karman Ghia Flow over a hump is an example of a turbulent separated flow. This flow is characterized by a simple geometry, but, nevertheless, is rich in many complex flow phenomena such as shear layer instability, separation, reattachment, and vortex interactions. The baseline case has been successfully simulated by the flow solver used in this work (Gan \textit{et. al.}, 2007). The flow is simulated at a Reynolds number of 371,600, based on the hump chord length, $C$, and Mach number of 0.04. The flow control is being achieved via a slot at approximately 65{\%} $C$ by using steady suction, and with alternate suction/blowing. Solutions will be presented for the three-dimensional RANS SST, steady and unsteady, turbulence model and DES and LES turbulence modeling approaches. Mean-velocity contours and turbulent kinetic energy contours will be examined. Detailed comparisons will be made of mean and turbulence statistics such as the pressure coefficient, skin-friction coefficient, and Reynolds stress profiles, with experimental results. The location of the reattachment behind the hump will be compared with previously published numerical simulations and experimental results. The successful control of this turbulent separated flow will cause a reduction in the reattachment length, compared with the uncontrolled case. [Preview Abstract] |
Sunday, November 18, 2007 12:18PM - 12:31PM |
BO.00009: Active control of turbulent heat transfer by local forcing: an energy assessment Guillermo Araya, Stefano Leonardi, Luciano Castillo The influence of local forcing on a turbulent channel flow is numerically investigated. The high level of information provided by Direct Numerical Simulations (DNS) allows an exhaustive analysis of the physical mechanism responsible for heat transfer enhancement. Budgets and energy spectra of the velocity and temperature correlations are computed at several forcing frequencies and compared with the unperturbed channel results. A maximum local skin friction reduction of approximately 32{\%} together with local increases of molecular heat fluxes up to 50{\%} are accomplished at a dimensionless frequency of 0.64 in the vicinity of the forcing source. Furthermore, wall-normal turbulent heat fluxes experience a significant augmentation of approximately 21{\%} at this forcing frequency. [Preview Abstract] |
Sunday, November 18, 2007 12:31PM - 12:44PM |
BO.00010: Flow-State Estimation Using Wall Information in a Transitional Boundary Layer. Ahmed Naguib, Jonathan Morrison This work is motivated by the overarching goal of implementing feedback control of transient growth in boundary-layer transition. An essential step towards such implementation is the ability to estimate the flowfield through surface measurements, coupled with low-order, efficient models. In the present study, a DNS database (Zaki - Ph.D. thesis, Stanford, 2006; Zaki and Durbin - JFM, 531, 2005) of bypass transition beneath a turbulent freestream is utilized for the assessment of flow-state estimation methods based on streamwise and spanwise surface-shear-stress measurements. The main focus of the investigation is on the estimation of the wall-normal velocity due to its significance in the resonant forcing of Squire modes. The results enable examination of the accuracy of the estimation approach through comparison between the estimated and true velocity fields. Moreover, practical issues, such as the number and configuration of wall sensors required for satisfactory estimation, are also addressed. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700