Entrainment characteristics of unsteady subsonic jets

The effectiveness of jet unsteadiness in enhancing flow entrainment was assessed. It was conducted that entrainment depends on the type and amount of jet unsteadiness. Apparently, the mere introduction of jet unsteadiness by small sinusoidal flow angle variations is insufficient to enhance entrainment but, it should be noted that the results were obtained at measuring stations which are all many nozzle widths downstream of the jet nozzle. Thus, no fully conclusive statement can be made at this time about the entrainment close to the nozzle. The high entrainment of the fluidically oscillated jet was caused by the high-frequency content of this square wave type of oscillation but more detailed measurements are clearly needed, in particular for the fluidically oscillated and the pulsed jets. Practical ejector application requires the proper trade-off between entrainment and primary nozzle thrust efficiency

Tricks and treats: designing technology to support mobility assistance dogs

Assistance dogs are a key intervention to support the autonomy of people with tetraplegia. Previous research on assistive technologies have investigated ways to, ultimately, replace their labour using technology, for instance through the design of smart home environments. However, both the disability studies literature and our interviews suggest there is an immediate need to support these relationships, both in terms of training and bonding. Through a case study of an accessible dog treats dispenser, we investigate a technological intervention responding to these needs, detailing an appropriate design methodology and contributing insights into user requirements and preferences

Response to stream temperature perturbations at higher frequencies of finite aspect ratio hot-wire anemometers

A finite-length hot-wire anemometer sensor, operated in air at a very low overheat ratio so as to act as a resistance thermometer does not respond to stream temperature perturbations with frequencies near the wire's corner frequency, like a single time-constant system, that is, a simple pole. This is contrary to presently available theoretical predictions based on the assumption of constancy of temperature at the wire ends under dynamic conditions. A simple lumped-parameter model is postulated which introduces a transition zone at the ends of the wire with a corner frequency different from that of the wire thus permitting the temperature of the wire ends to fluctuate

Measurement of Instantaneous Fluid Temperature and Two Fluid Velocity Components Using Hot-Wire Anemometers

Hot-wire anemometers, when used in a nonisothermal flow field, respond to both fluid temperature and fluid velocity fluctuations, even when operating conditions are selected to minimize the response to one of the stimuli. Use of a two- or three-wire array for the simultaneous measurement of temperature and velocity fluctuations and their mutual statistics has been shown to lead to significant errors, if, as is general practice, the approximate sensor responses are assumed to be ideal responses. An extension of the traditional techniques is described which eliminates this major source of error but still retains the simplicity of signal processing of the earlier methods. Copyrigh

Effect of mounting systems on heat transfer from inclined cylinders in cross-flow

Previous studies have shown that heat conduction to mounting systems significantly affects the heat transfer characteristics of cylinders in cross-flow unless the length-to-diameter ratio is large, typically over 1000. For inclined cylinders in cross-flow an additional effect exists due to significant aerodynamic interference of the cylinder supports with the flow. The effective cooling velocity, C, of inclined cylinders such as hot-wire anemometer sensors is frequently described in terms of the velocity with the cylinder normal to the flow, U, and the angle between the cylinder normal and the flow, α, by C = U(cos2 α + K2 sin2 α)0.5 Extensive investigations have indicated that k2 is predominantly a function of the cylinder length-to-diameter ratio. Arguments are presented which show that the k2 term describes the effective turning of the flow through a small angle. This interpretation shows that for narrow support spacings, flow channelling by the supports, which causes the flow to be more normal to the cylinder, gives the apparent increase in cooling above the 'cosine law' so frequently reported. New measurements with inclined hot-wire anemometers show that when interference with the flow over the cylinder is expected to be a minimum, that is, at large length-to-diameter ratios, typically larger than 1000, k2 assumes negative values

Entrainment characteristics of unsteady subsonic jets. [for V/STOL aircraft]

SEE ParentDocumentRecord|Ntt=19800001868 "NASA. Ames Res. Center Workshop on Thrust Augmenting Ejectors"; p. p 311-324The effectiveness of jet unsteadiness in enhancing flow entrainment was assessed. It was conducted that entrainment depends on the type and amount of jet unsteadiness. Apparently, the mere introduction of jet unsteadiness by small sinusoidal flow angle variations is insufficient to enhance entrainment but, it should be noted that the results were obtained at measuring stations which are all many nozzle widths downstream of the jet nozzle. Thus, no fully conclusive statement can be made at this time about the entrainment close to the nozzle. The high entrainment of the fluidically oscillated jet was caused by the high-frequency content of this square wave type of oscillation but more detailed measurements are clearly needed, in particular for the fluidically oscillated and the pulsed jets. Practical ejector application requires the proper trade-off between entrainment and primary nozzle thrust efficiency.Approved for public release; distribution is unlimited

Flow interference effect with parallel array hot-wire anemometer probes

Parallel array hot-wire anemometers with streamwise separation give good spatial resolution due to their small size in a direction normal to their common plane. In the case of velocity-temperature measurements, the upstream wire is operated as a resistance thermometer, thus leaving no thermal wake. Two previous studies show strongly conflicting results regarding the momentum wake. An improved method of detection and assessing the presence of such a wake is outlined. It is shown that the resultant velocity defect is significant and that its effect is a function of Reynolds number. Use of offset wires minimises this effect while still retaining good spatial resolution