Interaction between Two Jets Exhausted from Nozzles Arranged in Parallel

This paper describes flow structures of two interacting free jets expanded from uniform sonic nozzles into a stagnant ambient gas region. The Euler equations are numerically solved using a TVD (Total Variation Diminishing) scheme developed by Chakravarthy and Osher. First, a choked underexpanded supersonic single free jet is investigated in detail in the context of continuum ideal gas dynamics. By comparing the numerical results so obtained with the experimental ones it is confirmed that the present scheme is reliable. Second, the effect of the distance between the nozzle centerlines on the flow field of the two jets interacting with each other is examined from an analytical standpoint. Thereby, we find that a perfectly time-converged numerical solution is not reached at all, even at t→∞ (t : time). Rather, the solution may be regarded as quasi-steady or slightly oscillatory. Characteristic shock systems, density and pressure distributions of the interacting two free jets are quantitatively discussed in view of the numerical experiments. Also, a few fresh findings are described

Theoretical Analysis of Supersonic Gas-Particle Two-Phase Flow and Its Application to Relatively Complicated Flow Fields

This paper describes supersonic flows of a gas-particle two-phase mixture in considerably complicated situations. For the flow field of gas-particle mixtures such that the gas-phase and the particle-phase interact with each other, the model is constructed by incorporating the particle-trajectory method into the system of gas-phase equations in the two-fluid model. First, the one-phase and two-phase flows of round underexpanded jets exhausted from a sonic nozzle are investigated in detail. The one-phase results are compared with the experimental ones in order to confirm whether the present scheme is reliable or otherwise. For the two-phase results, the particles with the same velocity and temperature as those of the gas-phase are injected at the nozzle exit plane, and the effect of the presence of the particles on the flow field is examined by comparing these two-phase results with the one-phase ones. Second, the results of the numerical experiments in which underexpanded sonic round jets impinge on a flat plate normal to the jet axis are presented and analyzed for both the one-phase and two-phase cases. For the one-phase flow, periodic unstable oscillations have been found to give fairly good agreement with the experimental results. Third, supersonic gas-particle two-phase flows around a sphere are simulated in view of the numerical experiments. The instability in the particle motion near the stagnation region in the shock layer is discussed in detail. A few new findings are also described throughout the present paper

Theoretical Model of Two-Phase Flow in a Nozzle and Its Application to Numerical Experiments for Mist Flow

A numerical analysis of subsonic as well as supersonic nozzle flows of gas-particle mixtures is described. The theoretical model modified here is applied to the case where a gas-particle mixture is composed of air and water-particles in relation to the mist nozzle flow utilized for the secondary cooling zone of a continuously cast slab. For the subsonic nozzle flow, all of the flow properties are calculated on the basis of a given nozzle geometry with a parallel region. Next, for the supersonic nozzle, the so-called specified pressure method is applied to evaluate the behaviour of the gas-particle mixture in the flow field, as wel as to design the converging-diverging nozzle configuration according to the desired pressure profile. The results so obtained are examined and discussed from a numerical point of view

Heat transfer characteristics of a planar water jet impinging normally or obliquely on a flat surface at relatively low Reynolds numbers

The heat transfer characteristics of a planar free water jet normally or obliquely impinging onto a flat substrate were investigated experimentally. The planar jet issued from a rectangular slot nozzle with a cross section of 1.62 mm × 40 mm. The mean velocity at the nozzle exit ranged from 1.5 to 6.1 m s−1. The corresponding Reynolds number range based on the nozzle gap and the mean velocity was 2200–8800. Constant heat-flux conditions were employed at the solid surface. Various impingement angles between the vertical planar jet and the inclined solid surface were investigated: 90° (normal collision), 70°, 60°, and 50°. In the case of normal collisions, the Nusselt number is high at the impingement line, and decreases with departures from it. The stagnation Nusselt numbers were compared to the predictions of several correlations proposed by other researchers. In oblique collisions, the profiles of the local Nusselt numbers are asymmetric. The locations of the peak Nusselt numbers do not coincide with the geometric center of the planar jet on the surface

Free Flap Blood Flow Evaluated Using Two-Dimensional Laser Speckle Flowgraphy

Objective. We investigated the efficiency of laser speckle flowgraphy for evaluating blood flow in free flaps used for plastic surgery. Methods. We measured blood flow using a visual laser meter capable of providing two-dimensional color graphic representations of flow distribution for a given area using a dynamic laser speckle effect. Using laser speckle flowgraphy, we examined the blood flow of 20 free flaps applied following the excision of head and neck tumors. Results. After anastomosis of the feeding and draining blood vessels and sewing the flap, musculocutaneous (MC) flaps showed significantly lower blood flow than jejunal or omental flaps (P < .05). The ratio of blood flow decrease from the edge to the center was significantly greater in MC flaps than in jejunal or omental flaps (P < .001). Conclusion. Laser speckle flowgraphy is useful for the perioperative measurement of blood flow in free flaps used in plastic surgery. This method is a highly useful, practical, and reliable tool for assessing cutaneous blood flow and is expected to be applicable to several clinical fields

Capsaicin May Improve Swallowing Impairment in Patients with Amyotrophic Lateral Sclerosis: A Randomized Controlled Trial

Patients with neurodegenerative diseases are at an increased risk of dysphagia and aspiration pneumonia. In this study, we examined whether ingestion of capsaicin prior to swallowing changes the temporal dynamics of swallowing in such patients. In a crossover, randomized controlled trial, 29 patients with neurodegenerative diseases were given a soluble wafer containing 1.5 μg capsaicin or an identical placebo 20 min prior to testing. For evaluation with video fluoroscopy (VF), patients consumed a barium-containing liquid plus thickening material. The durations of the latency, elevating and recovery periods of the hyoid were assessed from VF. Overall, no significant differences were observed in the duration of each period between capsaicin and placebo treatments. However, reductions in the latency and elevating periods were positively correlated with baseline durations. In subgroup analyses, that correlation was observed in patents with amyotrophic lateral sclerosis (ALS) but not in patients with Parkinson’s disease. The consumption of wafer paper containing capsaicin before the intake of food may be effective in patients with dysphagia related with certain neurodegenerative diseases, particularly ALS patients. Further studies will be needed to validate this finding