Some Numerical Simulations and an Experimental Investigation of Finger Seals

All seal types have been shown to lift effectively, and experience only minor wear during startup. .. The double pad design outperforms previous seals, providing lower operating temperatures, and less leakage at higher pressures. .. Future experimentation at higher pressures, temperatures, and operating speeds will show the full potential of finger sealing technology

Thermomechanical Design Criteria for Ceramic-Coated Surfaces

Some early history of ceramic applications is presented. Finite element modeling of components to determine service and fabrication loads found inelastic behavior and residual stresses to be significant to component life. Inelastic behavior mitigates peak strains but enhances residual strains. Results of furnace, Mach 0.3 burner, and engine tests are discussed and categorized into design criteria (loading, geometry, fabrication, materials, analysis, and testing). These design rules and finite element analyses are brought to bear on two test cases: turboshaft engine seals, and rocket thrust chambers

A New Heating Configuration for Hydrothermal Crystal Growth Vessels to Achieve Better Thermal and Flow Environments

This paper presents a numerical investigation on a new heating configuration for hydrothermal crystal growth vessels. On the upper growth camber, the top wall is cooled and the sidewall is insulated while the lower chamber is heated on the side wall. The thermal environments in the autoclaves with the top wall cooling and the conventional sidewall-cooling configurations are compared. Results show that the top wall cooling configuration establishes a much better thermal and flow environment in the upper growth chamber. With the sidewall-cooling configuration, the flow consists of a jet-like flow along the vertical centerline and downward wall layers. Comparatively, with the top wall-cooling configuration, the three-dimensional unsteady swirling flow establishes a more homogeneous and isotropic thermal and flow environment in most of the space in the main growth region which is ideal for the crystal growth. In the lower dissolving chamber, which is heated on the sidewall, temperature is higher near the baffle and lower at the bottom. Such a temperature distribution guaranties the raw material on the top of the stack be dissolved first

Flow Structure and Transport Mechanism in Lower Half Heated Upper Half Cooled Enclosures in Laminar Flow Regime

This paper presents an investigation on the transport mechanism in autoclave/thermosyphon type enclosures. Without a baffle to separate the lower- from the upper-half, the flow structure and the transport mechanisms are the same in rectangular and cylindrical enclosures. Thus, the efficiency of the fluid exchange and heat transfer between the enclosure’s two halves due to wall-layers feeding structure ensures that the center cores have almost uniform temperature. However, when a baffle separates the two halves, the wall layers’ interactions are eliminated and two temperature zones are established

Non-Intrusive Laser-Based, Full-Field Quantitative Flow Measurements Aided by Digital Image Processing. Part 2: The Hydrostatic Journal Bearing

The full field flow tracking technique based on computer-aided image processing in combination with the non-intrusive particle tracking procedure described in Part 1 of this paper is used for quantification of qualitative images of flow in a six-pocket hydrostatic journal bearing. The method uses long distance microscopy (LDM) to evaluate at the same station in time, trajectories, velocities and accelerations throughout the flow field. For accurate and detailed evaluation, a new windowing procedure (WP) and an associated windowing assembly procedure (WAP) are introduced. The combination of WP and WAP brings together the LDM high magnification individually indexed windows into a global picture that yields a more thorough understanding of the total flow pattern

Three-Dimensional Heat Transfer and Fluid Exchange through Single-Hole Baffles in Industry Hydrothermal Autoclaves

Hydrothermal growth is the industrial method of preference to synthesize high-quality single crystals. The growth vessels, called autoclaves, are cylindrical containers filled with solutions of the crystal material. Under normal conditions, the fluid flows are three-dimensional. A baffle is used to partition the container into two chambers. This paper presents a systematic investigation on the transports through the baffle openings. Results indicate that a single-hole baffle is effective in controlling the fluid exchange and heat transfer between the two chambers. A smaller baffle opening establishes more uniform temperatures in the chambers. The flow structure shows that there is a pair of flow streams across the baffle opening. However, the heat exchange carried by this pair of streams, as well as heat exchange through molecular diffusion, is small. The transport through baffle opening is dominated by turbulence diffusion. Further heat transfer analysis shows that the characteristic length scale in industry growth vessels is a combination of the diameter of the baffle opening, the diameter of the autoclave, and the height of the chambers

EXPERIMENTAL VERIFICATION OF A NEW MODEL FOR TRANSITION FLOW OF THIN FILMS IN LONG JOURNAL BEARINGS

ABSTRACT A new model for predicting the flow behavior in long journal bearing films in the transition regime (Taylor and wavy vortex regimes) was previously proposed by the authors. This paper presents the experimental verification. A comparison between the experimental and numerical results of the TorqueSpeed graphs is presented with good agreement between the numerical and experimental data for the Couette, Taylor and pre-wavy regimes. In the wavy and turbulent regime, the magnitude of the numerically obtained data is larger than the corresponding measured torques, but the difference is confined to below 14%. A comparison between experimental and numerical flow patterns is also presented. The results match well in general, except that experimentally, a pre-wavy regime was identified. The latter is characterized by the disappearance of the Taylor vortices, while numerically the Taylor vortices are only distorted and the wavy vortices are formed in this regime. INTRODUCTION Most models are based fundamentally on the laminar flow theory, neglect the inertia effects, use the Reynolds equations [1], and work well before the onset of Taylor instabilities in journal bearing flow. Turbulence models embraced by the lubrication community use the Prandtl mixing length and the corresponding eddy viscosity concepts that imply the existence of a turbulent regime, which causes increased viscosity effects (Constantinescu's [2], Ng-Pan's [3], Hirs ' [4] and Gross et al. [5]). This approach accurately predicts the flow behavior and the four models are relatively close to each other when turbulence is truly fully developed, i.e. Reynolds number is larger than 2,000. However, in the transition regime, i.e. after the onset of Taylor vortices and before the full development of turbulence, the discrepancy amongst these most accepted models is significant. Deng and Braun [6

A Three-Dimensional Navier-Stokes–Based Numerical Model for Squeeze-Film Dampers. Part 1—Effects of Gaseous Cavitation on Pressure Distribution and Damping Coefficients without Consideration of Inertia

Even though most published results detailing damper behavior consider only the liquid phase, the cavitation process in the lubricant film, when it happens, is critical for the damper\u27s performance. A number of modeling approaches, such as the half-Sommerfeld and Elrod models, were proposed in order to account for the effects of cavitation on the pressure generation, without directly simulating the cavitation process. Based on the experimental data, a few other homogeneous cavitation models have also been developed. All these models are based on the classical Reynolds equation. In this article, a three-dimensional numerical model is developed and validated in connection with the operation of a two-phase squeeze-film damper. The full Navier-Stokes equations (NSE), coupled with a homogeneous cavitation model, is solved to simulate the flow of the two-phase lubricant film and the associated pressures. The pressure variation on the journal surface and the gas concentration distribution in the lubricating fluid (cavitated region) will be presented. The damping coefficients predicted by the NSE model are compared to the ones that resulted from the application of the Reynolds equation