Topic
Freestream
About: Freestream is a research topic. Over the lifetime, 3428 publications have been published within this topic receiving 56147 citations.
Papers published on a yearly basis
Papers
More filters
11 Jan 1993
TL;DR: In this paper, the behavior of a liquid-fuel spray transversely injected into a uniform high-speed crossflow has been characterized using a laser-sheet imaging technique, and the dependence of jet penetration upon jet-to-crossflow momentum ratio was studied by varying the ratio from 3 to 45.
Abstract: The behavior of a liquid-fuel spray transversely injected into a uniform high-speed crossflow has been characterized using a laser-sheet imaging technique. The dependence of jet penetration upon jet-to-crossflow momentum ratio was studied by varying the ratio from 3 to 45. The static pressure inside the test section was varied from 14.7 to 30 psia, while the freestream Mach number was held constant at 0.4. A detailed comparison of the jet trajectories (penetration profiles) measured in this study with those predicted by currently available correlation functions revealed gross discrepancies. These discrepancies were attributed to the fact that the spray plume consists of several zones, i.e., a liquid column adjacent to the injector and ligament and droplet regions, exhibiting different characteristics which cannot be adequately described by empirical functions. A composite functional form which takes into account the behavior of these fundamcntally different spray regions has been formulated to provide a more accurate description of the penetration profile of the spray plume. The proposed empirical formula also describes the maximum (asymptotic) penetration of the spray plume in the far field. The dependence of asymptotic penetration hcight upon momentum ratio was analyzed to yield a general formula for predicting the spray trajectory over a wide range of momentum ratios. d’
82 citations
09 Jan 2006
TL;DR: In this article, the velocity distributions upstream and downstream of a plasma actuator with an induced boundary layer were measured using freestream velocities of approximately 4.6 and 6.8 m/s for a range of frequencies (5-20 kHz) and voltages (7.5-10 kV amplitude).
Abstract: In previous work at the United States Air Force Academy, the phenomenology and behavior of the aerodynamic plasma actuator (a dielectric barrier discharge (DBD)) has been investigated. In order to provide additional insight into the phenomenology associated with the transfer of momentum to air by a plasma flow actuator, the velocity distributions upstream and downstream of a plasma actuator with an induced boundary layer were measured using freestream velocities of approximately 4.6 and 6.8 m/s for a range of frequencies (5-20 kHz) and voltages (7.5-10 kV amplitude). The body forces on the air were calculated using a control volume momentum balance. The results show that the body force acts in the sub-boundary layer region. For constant voltage, the body force is proportional to frequency producing a constant impulse per cycle, and the energy dissipation per cycle and efficiency are independent of frequency. The body forces are not affected by the freestream velocity.
81 citations
TL;DR: A 20-scale X-51A forebody model was tested in the Boeing/AFOSR Mach-6 Quiet Tunnel as discussed by the authors, and the effect of a smooth blank and two different trip strips on windward-forebody transition was measured using temperature sensitive paint and hot-wire anemometry.
Abstract: A 20%-scale X-51A forebody model was tested in the Boeing/AFOSR Mach-6 Quiet Tunnel. Repolishing the nozzle throat has restored quiet flow at high Reynolds numbers. The effect of a smooth blank and two different trip strips on windward-forebody transition was measured using temperature-sensitive paint and hot-wire anemometry. Reducing freestream noise from conventional to quiet levels increased the smooth-wall transition Reynolds number by a factor of at least 2.2. In addition, the transition Reynolds number based on the distance from the trips increased by a factor of 2.4 for the smaller trips and by a factor of 1.7 for the larger trips. Thus, tunnel noise had a substantial effect on roughness-induced transition.
80 citations
TL;DR: In this article, the effect of radiation on mixed convection from a vertical flat plate in a saturated porous medium is investigated and the conservation equations that govern the problem are reduced to a system of nonlinear ordinary differential equations.
80 citations
TL;DR: In this article, a boundary-layer transition study on a sharp, 5° half-angle cone at various angles of attack was conducted at Mach 3.5, and the transition was found to be less receptive to freestream acoustic disturbances than first-mode (Tollmien-Schlichting) dominated transition.
Abstract: A boundary-layer transition study on a sharp, 5° half-angle cone at various angles of attack was conducted at Mach 3.5. Transition data were obtained with and without significantly reduced freestream acoustic disturbance levels. A progressive downstream and upstream motion of the transition front on the windward and leeward rays, respectively, of the cone with angle of attack was observed for the high noise level data in agreement with data trends obtained in conventional (“noisy”) wind tunnels. However, the downstream movement was not observed to the same degree for the low noise level data in the present study. Transition believed to be crossflow dominated was found to be less receptive to freestream acoustic disturbances than first-mode (Tollmien-Schlichting) dominated transition. The previously-developed crossflow transition Reynolds number criterion, χtr,max≈200, was found to be inadequate for the current case. An improved criterion is offered, which includes compressibility and flow-geometry effects.
80 citations