Search

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The present work aims at the optimum design and the optimum operating condition of a S-shaped diffuser by studying the effect of inlet velocity, turning angle and area ratio using Computational Fluid Dynamics. Fluent 17.1 software has been used for this simulation work. It is found that the static pressure recovery coefficient (Cp) increases and the total pressure loss coefficient (Cl) decreases as the inlet velocity increases. It is also found that cross-flow velocity becomes more prominent as turning angle increases and the magnitude of in-plane velocity increases with the increase in area ratio. It is further found that flow separation at the bottom wall increases with the increment in area ratio and decreases with the increase in turning angle. Finally, it is found that AR 4 is the optimum area ratio and 75°/75° is the optimum turning angle. [ABSTRACT FROM AUTHOR]

An annular diffuser is a critical component of the turbomachinery, and its prime function is to reduce the flow velocity. The current work is carried to study the effect of four different geometrical designs of an annular diffuser using the ANSYS Fluent. The numerical simulations were carried out to examine the effect of fully developed turbulent swirling and non-swirling flow. The flow behavior of the annular diffuser is analyzed at Reynolds number 2.5 × 105. The simulated results reveal pressure recovery improvement at the casing wall with adequate swirl intensity at the diffuser inlet. Swirl intensity suppresses the flow separation on the casing and moves the flow from the hub wall to the casing wall of the annulus region. The results also show that the Equal Hub and Diverging Casing (EHDC) annular diffuser in comparison to other diffusers has a higher static pressure recovery (Cp = 0.76) and a lower total pressure loss coefficient of (CL = 0.12) at a 17° swirl angle. [ABSTRACT FROM AUTHOR]

In this paper, the effects of non-swirling and swirling flow on the performance of parallel hub axial annular diffuser has been investigated. The study was conducted on a fully developed swirling flow and non-swirling flow to predict the separation of the flow from the wall. Three different annular diffusers were used with casing wall angles of 3°, 6°, and 9°. Furthermore, various swirl angles (0–25°) at the inlet of diffusers have been investigated to analyze the performance across the length. It was found that parallel hub axial annular diffuser performance increases up to a certain length as the inlet swirl angle increases. However, the performance also improves as the diffuser area ratio (AR) increases. The performance is evaluated based on the static pressure recovery coefficient (Cp) and the total pressure loss coefficient (CTL). The highest possible pressure recovery is achieved by the 12° swirl angle with a casing angle of 6°. [ABSTRACT FROM AUTHOR]

In the present work, the parallel hub axial flow annular diffuser's performance characteristics with divergent casing varying between equivalent cone angle (10°, 15°, and 20°) with area ratio 3 have been evaluated computationally as well as experimentally. The performance of three diffusers was tested at different inlet swirl angles (from 0° to 25°) for swirling and nonswirling flow. Simulations have been carried out on a fully developed flow at Reynolds number 2.5×105. The results were analyzed based on the velocity profiles, static pressure recovery coefficient, and the total pressure loss coefficient. The result analysis shows that the inlet swirl flow improves the recovery of pressure and also delays the flow separation on the casing. Moreover, the findings also show that the best performance was achieved in equivalent cone angle 10° at the inlet swirl angle of 7.5° compared to other diffusers. [ABSTRACT FROM AUTHOR]

Aiming at the problem of gas turbine radial exhaust diffuser strut aerodynamic, the original aerodynamic profile of the strut was optimized with the NACA airfoil and two new aerodynamic profiles were designed. The steady-state and transient numerical simulation method were used to study the 10%, 50% and 90% radial height sections Mach number distribution of diffuser, total pressure loss coefficient of strut downstream, static pressure, static pressure recovery coefficient, the passage vortex, outlet static entropy of the exhaust diffuser and effect of turbine final stage wakes on exhaust diffuser static pressure recovery coefficient. Steady-state results indicate that the new struts delay the separation, strut downstream total pressure loss coefficient is reduced, and static pressure recovery coefficient of the exhaust is obviously improved. The transient results indicate that the final stage vane and rotor wakes have little effect on the static pressure recovery coefficient of the radial exhaust diffuser. [ABSTRACT FROM AUTHOR]

Aerodynamic studies in the static components of a centrifugal compressor stage were conducted using the computational fluid dynamics solver FLUENT. For the simulation study, a typical centrifugal compressor stage geometry with a flow coefficient of 0.053 was chosen, The study is confined to the static components of the centrifugal compressor stage, i.e., the crossover bend (180° U-bend), a radial cascade of return channel vanes, and the exit ducting (90° L-turn). The aerodynamic performance is reported in terms of total pressure loss coefficient, static pressure recovery coefficient, return channel vane surface static pressure distribution, and stage exit swirl angle distribution. The simulated flow through the static components covered five different operating conditions of the actual centrifugal compressor stage: the design point with 100% flow rate, and the off-design operating conditions with 70%, 80%, 110%, and 120% flow rates. The standard k-ε model was used with standard wall functions to predict the turbulence. A minimum total pressure loss coefficient was observed near 80% flow rate when the average flow angle at the U-bend inlet was 24°. Better static pressure recovery was observed with 70%, 80%, and 100% flow rates. The swirl angle distribution at the stage exit was recognized as satisfactory.

This work focuses on a numerical study of compressible subsonic flow in gas turbine annular diffusers. A diffuser is a diverging passage in which the flow is decelerated and the reduction in velocity head is converted to a rise in static pressure. Usually, for aircraft engines, and also for many industrial engines, the length is a crucial restriction, with the result that the diffuser shape should be at the shortest possible distance. However, with an increase in divergence angle, stall losses arising from boundary-layer separation become more significant and the pressure recovery coefficient is affected. Hence, it is important to study the divergence angle as a function of the airflow behavior. In the numerical solution, mass, momentum and energy equations are discretized and solved employing the finite volume method, and the turbulence effects are taken into account using the realizable k-s model with an enhanced wall treatment. The results showed that the annular diffuser performance is insensitive to Mach number for the divergence angle equal to 9°. On the other hand, the pressure recovery coefficient elevates as the Mach number increases for the divergence angle equal to 6°. The opposite phenomenon occurred for 12° diffuser due to the intense recirculation zones as the divergence angle increases. [ABSTRACT FROM AUTHOR]

In an effort to improve the performance of centrifugal compressors, detailed studies were carried out on three different impeller-diffuser configurations covering a wide range of design flow coefficients. These were two-dimensional impellers chosen from a multi-stage compressor series with identical blade geometry. The impeller exit widths covered were 24.5, 18.5, and 11.5 mm, respectively. Extensive experimental studies have been carried out on the chosen stage configurations with parallel walled vaneless diffusers (VLDs) as well as low solidity vaned diffuser (LSD). For all the tested configurations, the aerofoil shape of the diffuser vanes remained same while the diffuser width, setting angle, and solidity were chosen as variables. The performance for each of the stages with LSDs was compared with that of the corresponding VLD. Significant improvement in performance in terms of polytropic efficiency, head coefficient, and static pressure recovery coefficient was observed with LSD vanes as compared with the VLD. Significant improvement in performance was noticed from low flow till design point for all the tested cases. The study revealed that among the tested configurations, there is an optimum width at impeller exit and diffuser for which the performance of the stage was the best. Performance in terms of static pressure recovery coefficient was also evaluated for all the tested configurations and compared. All the studies were conducted for solidity ratio of 0.81. The effect of setting angle on wall static pressure coefficient was also studied at 24° and 28° for the flow coefficients corresponding to 80, 100, and 120 per cent of design flow. Flow surveys at impeller exit for the three cases covering impellers/parallel walled diffusers of different widths have also been carried out to know the flow behaviour in the passage between the impeller and the diffuser. [ABSTRACT FROM AUTHOR]

Annular diffusers are an integral component of the gas turbine engines of high-speed aircraft. These facilitate effective operation of the combustor by reducing the total pressure loss. The performance characteristics of these diffusers depend on their geometry and the inlet conditions. The present investigation attempts to select the range of the inlet swirl intensity for the best performance of annular diffusers with different geometries but having the same equivalent cone angle. This is analysed on the basis of the static pressure recovery and total pressure loss coefficients. The results show that the parallel diverging hub and casing annular diffuser produces the best performance at high-swirl intensities. [ABSTRACT FROM AUTHOR]