A Numerical Analysis of the Influence of Nozzle Geometric Structure on Spontaneous Steam Condensation and Irreversibility in the Steam Ejector Nozzle

The spontaneous condensation of wet steam often occurs in the steam ejector nozzle, this deteriorates the performance of the steam ejector. In this paper, we take changing the geometric parameters of the nozzle as the focus of our research and construct an internal connection between steam’s condensation behavior and the nozzle’s throat radius, the nozzle’s divergent section expansion angle, and the nozzle’s divergent section length. Our numerical simulation results indicate that an increase in the throat diameter and reduction of the divergent section’s expansion angle can inhibit steam condensation behavior, to a certain extent. In particular, the steam condensation behavior will disappear at a 0° expansion angle, but it is not affected by the change in the divergent section’s length. In addition, the irreversibility that is seen under different changes to the nozzle’s structure parameters was investigated and the results show that the entropy generation that is caused by a phase change accounts for a much higher proportion of the total entropy generation than heat transport and viscous dissipation do. This indicates that steam’s condensation behavior makes a large amount of irreversible energy, resulting in energy waste and reducing the performance of the nozzle. Therefore, this study can provide a theoretical reference for suppressing the spontaneous condensation behavior of steam by changing the nozzle’s geometry.

FILM COOLING EFFECTIVENESS MEASUREMENT OF FAN-SHAPED HOLES MANUFACTURED USING EDM TECHNIQUE

In this study, the influence of geometric factors such as hole diameter (D), length-to-diameter ratio (L/D), injection angle (a), and lateral expansion angle (α) on film cooling effectiveness of holes made using EDM is experimentally investigated. Nine different cooling configurations were tested on a flat plate wind tunnel at various coolant Reynolds number (Rec) and coolant to mainstream blowing ratio (M). The considered flat plate model incorporates engine sized V-shaped holes. EDM reliability is assessed through a hole qualification process, while effectiveness was measured by the Pressure Sensitive Paint (PSP) technique. Results confirm the suitability of EDM for V-shaped hole manufacturing as long as a correct tolerance on α is prescribed. An accurate qualification of hole morphology is also recommended.

Effects of Cowl-Induced Expansion on the Wave Complex Induced by Oblique Detonation Wave Reflection

Oblique detonation wave (ODW) reflection on the upper wall leads to a sophisticated wave complex, whose stability is critical to the application of oblique detonation engines. The unstable wave complex characterized with a continuous moving Mach stem has been observed, but the corresponding re-stability adjusting method is still unclear so far. In this study, the cowl-induced expansion wave based on the model with an upper-side expansion wall is introduced, and the ODW dynamics have been analyzed using the reactive Euler equations with a two-step induction–reaction kinetic model. With the addition of a cowl-induced expansion wave, the re-stabilized Mach stem has been distinguished. This re-stability is determined by the weakened secondary reflection wave of lower wall, while the final location of Mach stem is not sensitive to the position of the expansion corner. The re-stabilized ODW structure is also basically irrelevant to the expansion angle, while it may shift to unstable due to the merging of subsonic zones. Transient phenomena for the unstable state have been also discussed, clarifying fine wave structures further.

Effect of Mainstream Velocity on the Optimization of a Fan-Shaped Film-Cooling Hole on a Flat Plate

In this study, the effect of mainstream velocity on the optimization of a fan-shaped hole on a flat plate was experimentally investigated. The experiment was conducted by changing the forward expansion angle (βfwd), lateral expansion angle (βlat), and metering length ratio (Lm/D) of the film-cooling hole. A total of 13 cases extracted using the Box–Behnken method were considered to examine the effect of the shape parameters of the film-cooling hole under a 90 m/s mainstream velocity condition, and the results were compared with the results derived under a mainstream velocity of 20 m/s. One density ratio (DR = 2.0) and a blowing ratio (M) ranging from 1.0 to 2.5 were considered, and the pressure-sensitive paint (PSP) technique was applied for the film-cooling effectiveness (FCE). As a result of the experiment, the optimized hole showed a 49.3% improvement in the overall averaged FCE compared to the reference hole with DR = 2.0 and M = 2.0. As the blowing ratio increased, the hole exit area tended to increase, and this tendency was the same as that in the 20 m/s mainstream condition.

Film Cooling Effectiveness Measurement of Fan-Shaped Holes Manufactured Using EDM Technique

In this study, the influence of geometric factors such as hole diameter (D), length-to-diameter ratio (L/D), injection angle (α), and lateral expansion angle (β) on film cooling effectiveness of holes made using EDM is experimentally investigated. Nine different cooling configurations were tested on a flat plate wind tunnel at various coolant Reynolds number (Rec) and coolant to mainstream blowing ratio (M). The considered flat plate model incorporates engine sized V-shaped holes. EDM reliability is assessed through a hole qualification process, while effectiveness was measured by the Pressure Sensitive Paint (PSP) technique. Results confirm the suitability of EDM for V-shaped hole manufacturing as long as a correct tolerance on β is prescribed. An accurate qualification of hole morphology is also recommended.

Experimental Investigation of the Confinement Effects in Radial-Radial Swirlers

This experimental study investigates the effect of confinement ratio (CR) on the flow field of a counter-rotating radial-radial swirler. Two-dimensional two-component (2D2C) particle image velocimetry (PIV) measurements are performed at the mid-plane of the jet. Four different confinement ratios (i.e., 10.4, 23.4, 41.6 and unconfined) are considered at a swirl number of 1.2. The results reveal the presence of a central toroidal recirculation zone (CTRZ) in all cases extending inside the jet which indicates the existence of an adverse pressure gradient. For the unconfined swirling jet, the recirculation zone is small in size and exists at the exit of the jet. For the CR = 41.6 case, on the other hand, there exist two separate recirculation zones with the first one being similar to the unconfined case in terms of size and axial position, while the second one being larger in size and positioned at a more downstream location. Variation of the axial velocity along the centerline of the jet for this case indicates the presence of an adverse pressure gradient only in the close-jet region correlated with the first recirculation zone. For the smaller CR values, a single massive CTRZ emerges. This leads to increase in the expansion angle of the swirling jet as the CR decreases. Correspondingly, the radial velocity at the jet exit increases. For the confined cases with a single recirculation zone, the length and the width to cross-section ratio increase with the CR. On the other hand, the ratio of the reverse flow rate to total mass flow rate decreases with increasing CR values.

Parametric Optimization of Film Cooling Hole Geometry

In this study, a combination of computational simulation and experimental testing was used to evaluate a broad range of forward and lateral expansion angles for a turbine film cooling shaped holes. The study demonstrates the utilizing of RANS based CFD to quickly screen potential optimized geometries, followed by experimental determination of true performance characteristics. As a baseline, the performance of all film cooling holes was evaluated using an internal coolant channel cross-flow. Also, all hole geometries incorporated a filleted inlet-plenum interface, which presumes use of additive manufacturing to construct the turbine components. Experimental validation confirmed that the computational simulations predicted the correct relative performance of various hole geometries, even though actual performance levels were not predicted well. This investigation showed that the performance of laidback, fan shaped holes was much more sensitive to the lateral expansion angle than the forward expansion angle. The optimum shaped hole configuration was found to be a hole with a 15° lateral expansion angle and a 1° forward expansion angle (15-15-1 configuration), which had a maximum average adiabatic effectiveness 40% greater than the baseline 7-7-7 open literature hole. This study also showed that the shaped hole diffuser performance is primarily a function only three parameters: the coolant jet velocity ratio, VR, the shaped hole area ratio, AR, and the hole exit width relative to the pitch between holes, t/P.

Influence of Gas Density and Plug Diameter on Plume Characteristics by Ladle Stirring

The paper presents new results concerning the influence of the gas density and porous plug diameter on the nature of liquid steel stirring with an inert gas in the ladle. The tests were carried out on a cold model of a 30t ladle using particle image velocimetry (PIV) with a high-speed camera to analyse the plume zone formed during the supply of argon and helium as a stirring gas. The similarity criteria for the investigation of stirring processes in cold model in the past were discussed and compared. The modified Morton number was used in this paper to relate the gas flow rate in the model with real objects. The presented results constitute complete documentation of the influence of the plug diameter and gas density on the size of formed gas bubbles and the velocity of gas bubbles rising in different zones of the plume, plume, and spout geometry, including the expansion angle, spout height, open eye area, and gas hold-up.

Shape Optimization of Labyrinth Seals to Improve Sealing Performance

To reduce gas leakage, shape optimization of a straight labyrinth seal was carried out. The six design parameters included seal clearance, fin width, fin height, fin pitch, fin backward, and forward expansion angle. The CFD (Computational Fluid Dynamics) model was solved to generate the training and testing samples for the surrogate model, which was established by the least square support vector machine. A kind of chaotic optimization algorithm was used to determine the optimal design parameters of the labyrinth seal. As seal clearance, fin width, fin height, fin pitch, fin backward and forward expansion angles are 0.2 mm, 0.1 mm, 7 mm, 9 mm, 0°, and 15°, the discharge coefficient can reach its minimum value in the design space. The chaotic optimization algorithm coupled with least square support vector machine is a promising scheme for labyrinth seal optimization.