Go-Long Tsai

Separated-Reattaching Flow Over a Backstep With Uniform Normal Mass Bleed (Data Bank Contribution)

The effect of normal mass bleed into the separated-reattaching flow behind a backward-facing step has been experimentally investigated. Results of LDA measurements showed that normal mass bleed suppressed the reverse horizontal velocity, the reverse flow rate, turbulence intensity, and Reynolds shear stress within the whole recirculating zone. An analysis of the distributions of vertical velocity and turbulence intensity indicates that the interaction between the injected fluid and the main stream began at 0.4 step height and became significant after 0.8 step height behind the backstep.

Flame stabilization in the wake flow behind a slit V-Gutter

Abstract The features of flame stabilization of a V-shaped flame holder with a slit at the leading edge have been investigated by flow visualization and measurements of velocity, turbulence intensity, pressure, and temperature in the near wake. The results indicate that the stable operating limits of the flame holder were significantly improved at an optimal ratio of the slit width to the span width of the flame holder. The mechanism that kept the flame stabilized over the slit V-gutter is different from the traditional one. Observation of the flow showed that a diverted flame sheet was generated between two wings and merged gradually with the adjacent reacting shear layer to form a lumped flame kernel, which remained stable in the wake region. A jet-flame-like structure produced in the lower reacting layer and the recirculation zone shifted upward in the near wake. The turbulence intensity in the core of the near wake was increased by the effect of the diverted jet through the slit. The flame configurations provided extra thermal energy to sustain the flame and resulted in a local maximum temperature that enhanced combustion in fuel-rich conditions. All evidence indicates that the slit V-gutter extends the operating limits of the flame holder and is more stable than the traditional one.

Near-Wake Flow of a V-Gutter With Slit Bleed (Data Bank Contribution)

The cold-flow characteristics of a v-shape flame holder with flow bleed from a slit located at the leading edge have been investigated. According to experimental evidence, a nonsymmetric wake structure is developed behind the symmetric slit v-gutter. The flow through the slit induces greater reverse flow and greater back pressure in the near wake. It also provokes more extensive transport across the shear layers and reduces both the turbulent intensity and the Reynolds shear stress of the wake flow. These results indicate that the slit v-gutter can have a better flame holding ability and less pressure loss compared with the traditional v-gutter. In view of fluid dynamics features, the slit v-gutter is indeed a potentially useful design of flame holder.

The wake flow structure of an open-slit V gutter

Abstract This work experimentally investigates the near-wake flow structure behind an open-slit V gutter at airflow speeds between 1 m/s and 20 m/s. With the aid of Schlieren photography and a Dantec three-beam, two-component laser-Doppler anemometry system, the phenomena of vortex shedding and flow recirculation behind the flameholder are well investigated. The results indicate that the interaction between the flow penetrating through the open slit and the shear layer results in an asymmetric wake flow structure. The lower shear layer develops more stably and smoothly than the upper shear layer. Besides, the vortex formation along the lower wing is delayed and at a location farther downstream. The size of the entire recirculation zone is enlarged, and its center shifts toward one of the two wings. Measurements of wake pressure distribution show that the open-slit V gutter generates higher back pressure and thus induces less drag force than the regular V gutter. Moreover, the maximum values of the pressure fluctuation of the wake flow behind the open-slit V gutter reduce 27% and 9%, for the upper side and the lower side, respectively, much lower than those of the regular V gutter. In general, the application of mass bleed from the open-slit V gutter favors both the flame-holding mechanism and the suppression of the flow-induced oscillation.

NON-INVASIVE TECHNIQUE FOR IN VIVO HUMAN EAR CANAL VOLUME MEASUREMENT

This prospective study is to develop a new non-invasive in vivo technique for the measurement of the human external auditory canal (EAC) volume using high resolution computed tomography (HRCT). Eighteen ears of nine male volunteers, with an age range of 20–30, were measured. The EAC volume was measured using three different methods: tympanometry, water injection, and HRCT. Two dimensional image slices of the EAC, in vivo, were obtained from the raw HRCT data. Each 2D CT image slice was composed of 512 × 512 pixels, with a 0.5 mm slice thickness, and a 0.175 × 0.175 × 0.5 mm3 voxel size. HRCT images were processed with Amira® software (Visage Imaging, Inc., San Diego, USA). Three-dimensional images of the EAC were reconstructed using an unconstrained smoothing mode. The resulting volume of the 3D model of the EAC was calculated using a voxel gate stacked tool. Using tympanometry, the mean measured EAC volume, averaged over all ears, was 766.66 mm3 (Standard Deviation, SD = 194.03 mm3). Using water injectio...

Thermal performance of a plate-fin heat sink with a shield

To assess the performance of plate-fin heat sinks with the introduction of a shield in a cross flow, we analyzed the surface temperature of the base of the heat sink with an infrared thermograph to determine the effects of shield, fin height, fin width and Reynolds number on the thermal resistance. The introduction of a shield decreases the bypass flow effect and forces more coolant fluid to enter the channel from fin to fin to enhance the heat transfer. Increasing the Reynolds number decreases the thermal resistance of the heat sink, but that decrease tends to diminish with increasing Reynolds number. For a given fin width, the thermal performance of the heat sink with the highest fins is superior. For a given fin height, the optimal fin width in terms of thermal performance increases with increasing Reynolds number.

Effects of horizontal piezoelectric fan arrangement on the forced convection flow field of a pin-fin heat sink

In this study, a horizontal piezoelectric fan is used to realize forced convection in a pin-fin heat sink. In addition, the resulting forced convection flow field is investigated using numerical simulation methodologies (ANSYS CFD/Fluent). The swinging of the piezoelectric fan caused by the inverse piezoelectric effects of the piezoelectric materials actualized the movement of the thin fin and convection of the surrounding fluid, resulting in heat dissipation. The piezoelectric fan exhibited several advantages, including miniaturization, low energy consumption, and low noise. As the distance from the fore-end of the horizontal piezoelectric fan to that of the radiator remained constant (Lg = 5 mm), the heat dissipation efficiency of the pin-fin heat sink increased with the distance from the center of the piezoelectric fan to the baseboard (Hw). This was attributed to the impinging jet generated by the swinging of the piezoelectric fan. The optimal parameters for heat dissipation within the pin-fin heat sink were demonstrated to be Lg = 5 mm and Hw = 30 mm.

The effect of intake manifolds on cylinder-to-cylinder variations of performance and emissions of a four-cylinder engine

Abstract This paper deals with the influences of unequal length and unequal diameter of intake pipes on the cylinder‐to‐cylinder variation of volumetric efficiency, NO emission, CO emission, and other typical simulation results of engine performance. It is found from the present study that, due to the water‐hammer effect, the cylinder with the longer intake pipe has a higher volumetric efficiency than that with the shorter pipe. The phenomenon is especially evident at high engine speed. In addition, the decrease of the intake pipe diameter has an effect which is similar to that of the increase of the intake pipe length, but the inertia of the inlet mixture is reduced by the pipe wall friction at high engine speed. Shortening the intake pipe length of one of the cylinders has an effect on the engine performance and emissions which is similar to the effect of increasing the intake pipe length of the other cylinder. At low rpm, NO emission is inversely proportional to the volumetric efficiency because of the...