scispace - formally typeset
Search or ask a question
Topic

Freestream

About: Freestream is a research topic. Over the lifetime, 3428 publications have been published within this topic receiving 56147 citations.


Papers
More filters
Journal ArticleDOI
TL;DR: In this article, the aeroacoustic environment of an open cavity with a length-to-depth (LID) ratio of 1.0 was studied with and without plasma actuators.
Abstract: The aeroacoustic environment of an open cavity with a length-to-depth (LID) ratio of 1.0 was studied with and without plasma actuators. The study was conducted through low-speed wind-tunnel experiments at freestream velocities between 10 and 20 m/s, corresponding to Reynolds numbers based on the depth of the cavity of 3.6 x 104 to 7.1 x 10 4 . The fluid flow inside the cavity was studied using a range of measurement techniques, which include oil flow, particle imaging velocimetry, and surface-mounted-microphone measurements. For acoustic control, an array of plasma actuators were located on the approaching surface to the cavity, aligned with the direction of the oncoming flow. Results show that the plasma actuators lead to a significant attenuation of the dominant cavity mode. The particle imaging velocimetry surveys around the electrode elements reveal vortical structures produced by the plasma actuators. These structures convect downstream with the mean flow and produce spanwise variations in the flow over the cavity that affect the spanwise coherence of the shear layer and hence the corresponding Rossiter mode.

44 citations

Journal ArticleDOI
TL;DR: In this article, the authors evaluate the transient effects of a reaction control jet on the aerodynamic performance of a generic interceptor at different altitudes and thruster conditions, and the results are used to determine the ine uence of the jet-interaction effects on the transient aerodynamicperformance of the interceptor.
Abstract: The objective is to evaluate the transient effects of a reaction control jet on the aerodynamic performance of a genericinterceptormissileoperating at supersonice ightconditions.Three-dimensionalcomputationsofthehighly turbulent e owe eld produced by a pulsed, supersonic, lateral-jet control thruster interacting with the supersonic freestream and missile boundary layer of a generic interceptor missile are evaluated at different altitudes and thruster conditions. A generic missile interceptor cone guration consisting of a long, slender body containing e xed dorsal and tail e ns is simulated. Parametric computational e uid dynamic solutions are obtained at altitude conditions corresponding to 19.7 and 35.1 km for 1 ) steady-state conditions with the lateral control jet turned off, 2) steady-state conditions with the lateral control jet turned on, 3 ) transient jet startup conditions, and 4 ) transient jet shutdown conditions. A thermally and calorically perfect gas with a specie c heat ratio equal to 1.4 was assumed for both the Mach number 5 freestream and Mach number 3 lateral jet. Vehicle forces and moments are assessed from each solution by integrating the surface pressures and viscous shear stresses computed on the missile surfaces. These results are used to determine the ine uence of the jet-interaction effects on the transient aerodynamicperformanceofthemissile.Theanalysispredictsstrongtransientine uencesfortheintegratednormal force and pitching moment.

44 citations

Journal ArticleDOI
TL;DR: In this article, the influence of wind-tunnel turbulence on the development of a turbulent boundary was studied in the DFVLR-AVA at a freestream velocity of U^ = 20 m/s.
Abstract: The influence of the wind-tunnel turbulence on the development of a turbulent boundary was studied. The experiments were carried out in the low-turbulence wind tunnel of the DFVLR-AVA at a freestream velocity of U^ = 20 m/s. The turbulence level (Tut -0.06%) was increased up to Tuj «1% by means of various grids at different positions in the settling chamber or nozzle. For a fixed transition and constant distance from the nozzle throat, the effect of the wind-tunnel turbulence on the wall shear stress was investigated. In particular, an attempt was made to separate the effects which result from the turbulence intensity and from the turbulence structure, which is different in each wind tunnel.

44 citations

Journal ArticleDOI
16 Jul 2019-Energies
TL;DR: In this article, the authors examined three-dimensional, volumetric mean velocity fields and corresponding performance measurements for an isolated vertical-axis wind turbine (VAWT) and for co-and counter-rotating pairs of VAWTs with varying incident wind direction and turbine spacings.
Abstract: This study examined three-dimensional, volumetric mean velocity fields and corresponding performance measurements for an isolated vertical-axis wind turbine (VAWT) and for co- and counter-rotating pairs of VAWTs with varying incident wind direction and turbine spacings. The purpose was to identify turbine configurations and flow mechanisms that can improve the power densities of VAWT arrays in wind farms. All experiments were conducted at a Reynolds number of R e D = 7.3 × 10 4 . In the paired arrays, performance enhancement was observed for both the upstream and downstream turbines. Increases in downstream turbine performance correlate with bluff–body accelerations around the upstream turbine, which increase the incident freestream velocity on the downstream turbine in certain positions. Decreases in downstream turbine performance are determined by its position in the upstream turbine’s wake. Changes in upstream turbine performance are related to variations in the surrounding flow field due to the presence of the downstream rotor. For the most robust array configuration studied, an average 14% increase in array performance over approximately a 50° range of wind direction was observed. Additionally, three-dimensional vortex interactions behind pairs of VAWT were observed that can replenish momentum in the wake by advection rather than turbulent diffusion. These effects and their implications for wind-farm design are discussed.

44 citations

Proceedings ArticleDOI
29 Jun 1997
TL;DR: In this paper, the effects of active separation control on the aerodynamic performance of an advanced fighter aircraft configuration have been determined using a 7% scale lambda-wing model with jet actuators on the wing leading edge flaps.
Abstract: The effects of active separation control on the aerodynamic performance of an advanced fighter aircraft configuration have been determined. Lowspeed wind tunnel tests were performed using a 7% scale lambda-wing model with jet actuators on the wing leading edge flaps. The jets were operated in a pulsed mode and their frequency and amplitude were varied during the experiments. The effects of the jet actuators on the model aerodynamic performance were measured using a six component force balance for several flap configurations and for angles-of-attack (a) up to 40 deg. The results indicate that the pulsed jets are effective in delaying separation and augmenting lift. Maximum increases in lift were approximately 7% and occurred near C,max. Experiments performed to determine the influence of pulse frequency, ff, on control effectiveness showed that control was optimized for nondimensional frequencies, based on freestream velocity, UM, and wing chord, c, near Strc =/p c/Ura= 1. In addition, it was found that control effectiveness increased monotonically with increases in pulse amplitude. When operating the jet actuators on one wing alone, roll moment coefficients of CRoll- 0.011 could be produced. The results of these experiments indicate that leading edge pulsed jet actuators are an effective means of enhancing aerodynamic performance and maneuverability of advanced fighters.

44 citations


Network Information
Related Topics (5)
Reynolds number
68.4K papers, 1.6M citations
87% related
Boundary layer
64.9K papers, 1.4M citations
84% related
Turbulence
112.1K papers, 2.7M citations
81% related
Laminar flow
56K papers, 1.2M citations
81% related
Nozzle
158.6K papers, 893K citations
79% related
Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023195
2022350
2021108
2020113
201986
2018118