Numerical Investigation of Vaneless Diffuser by Pinching and Rotation

Energy Coefficient ◽

Pressure Recovery Coefficient ◽

Isentropic Efficiency

Abstract Non-conventional diffuser designs are introduced to minimize the energy losses associated with diffusion and to enhance stable operating range of the diffusion system. This is achieved by reducing width of the diffuser by modifying a hub or shroud curves by keeping the diffuser diameter ratio constant which is often known as pinch. The comparison of modified compressor with base model is accomplished by using performance characteristics such as static pressure recovery coefficient, stagnation pressure loss coefficient, energy coefficient and isentropic efficiency. Simulations are performed at various hub pinch (5%–20%), shroud pinch (5%–20%) and combined hub and shroud pinch (5%–20%). Among all the cases shroud pinch of 10% shows best results in terms of stagnation pressure loss coefficient, static pressure recovery coefficient and energy coefficient. Further, simulations are carried out with forced rotating vaneless diffuser. It gives better results in terms of pressure rise with lower stagnation pressure losses. But there is a moderate decrement in isentropic efficiency of compressor when compared to the base model.

Effects of casing angle on the performance of parallel hub axial annular diffuser

International Journal of Turbo and Jet Engines ◽

10.1515/tjj-2020-0019 ◽

2020 ◽

Vol 0 (0) ◽

Author(s):

Hardial Singh ◽

B.B. Arora

Keyword(s):

Static Pressure ◽

Swirling Flow ◽

Pressure Recovery ◽

Recovery Coefficient ◽

Swirl Angle ◽

Annular Diffuser ◽

Inlet Swirl ◽

Total Pressure Loss Coefficient ◽

Abstract 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°.

Effects of casing angle on the performance of parallel hub axial annular diffuser

International Journal of Turbo and Jet Engines ◽

10.1515/tjeng-2020-0019 ◽

2020 ◽

Vol 0 (0) ◽

Author(s):

Hardial Singh ◽

B.B. Arora

Keyword(s):

Static Pressure ◽

Swirling Flow ◽

Pressure Recovery ◽

Recovery Coefficient ◽

Swirl Angle ◽

Annular Diffuser ◽

Inlet Swirl ◽

Total Pressure Loss Coefficient ◽

AbstractIn 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°.

An Investigation of the Tapered Strut On Aerodynamic Performance of the Exhaust Diffuser Under Different Swirls

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4052383 ◽

2021 ◽

Author(s):

Yuxuan Dong ◽

Zhigang Li ◽

Jun Li

Keyword(s):

Pressure Loss ◽

Total Pressure ◽

Static Pressure ◽

Aerodynamic Performance ◽

Total Pressure Loss ◽

Pressure Recovery ◽

Flow Process ◽

Loss Mechanism ◽

Recovery Coefficient ◽

Abstract The exhaust diffuser with different struts was numerically calculated by solving three-dimensional Reynolds-Averaged Navier-Stokes (RANS). The flow process and flow loss mechanism in the diffuser were analyzed, the influence of two different structures of tapered struts on the aerodynamic performance of the exhaust diffuser under different inlet pre-swirls was explored, and the aerodynamic performance of the exhaust diffuser with tapered struts was compared with a conventional exhaust diffuser with linear struts. The results show that, compared with the conventional linear strut, under different inlet pre-swirls, two different tapered struts can both weaken the flow separation in the exhaust diffuser, thereby reducing the total pressure loss. When the inlet pre-swirl is greater than 0.35, the total pressure loss coefficient of the exhaust diffuser with structure-C tapered struts decreases by up to 0.07. The two types of tapered struts also change the flow structure at the exhaust diffuser outlet, which affects the uniformity of the outlet airflow, and then affect the static pressure recovery coefficient. Under different inlet pre-swirls, two types of tapered struts can be effective to increase the static pressure recovery coefficient of the exhaust diffuser, for the exhaust diffuser with structure-C tapered struts, the static pressure recovery coefficient can be increased by up to 0.065, relative increase of 20%. The research in this paper shows that the tapered structure can significantly improve the aerodynamic performance of the exhaust diffuser under different inlet pre-swirls.

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

Effect of the turning angle on the flow and performance characteristics of long S-shaped circular diffusers

10.1243/095441003763031815 ◽

2003 ◽

Vol 217 (1) ◽

pp. 29-41 ◽

Cited By ~ 8

Author(s):

R B Anand ◽

L Rai ◽

S N Singh

Keyword(s):

Total Pressure ◽

Static Pressure ◽

Area Ratio ◽

Secondary Flows ◽

Performance Characteristics ◽

Pressure Recovery ◽

Recovery Coefficient ◽

Turning Angle ◽

And Performance ◽

The effect of the turning angle on the flow and performance characteristics of long S-shaped circular diffusers (length-inlet diameter ratio, L/Di = 11:4) having an area ratio of 1.9 and centre-line length of 600 mm has been established. The experiments are carried out for three S-shaped circular diffusers having angles of turn of 15°/15°, 22.5°/22.5° and 30°/30°. Velocity, static pressure and total pressure distributions at different planes along the length of the diffusers are measured using a five-hole impact probe. The turbulence intensity distribution at the same planes is also measured using a normal hot-wire probe. The static pressure recovery coefficients for 15°/15°, 22.5°/22.5° and 30°/30° diffusers are evaluated as 0.45, 0.40 and 0.35 respectively, whereas the ideal static pressure recovery coefficient is 0.72. The low performance is attributed to the generation of secondary flows due to geometrical curvature and additional losses as a result of the high surface roughness (~0.5 mm) of the diffusers. The pressure recovery coefficient of these circular test diffusers is comparatively lower than that of an S-shaped rectangular diffuser of nearly the same area ratio, even with a larger turning angle (90°/90°), i.e. 0.53. The total pressure loss coefficient for all the diffusers is nearly the same and seems to be independent of the angle of turn. The flow distribution is more uniform at the exit for the higher angle of turn diffusers.

Some Studies on Low Solidity Vaned Diffusers of a Centrifugal Compressor Stage

Volume 6: Turbo Expo 2005, Parts A and B ◽

10.1115/gt2005-68972 ◽

2005 ◽

Author(s):

T. Ch. Siva Reddy ◽

G. V. Ramana Murty ◽

Prasad Mukkavilli ◽

D. N. Reddy

Keyword(s):

Centrifugal Compressor ◽

Static Pressure ◽

Pressure Ratio ◽

Pressure Recovery ◽

Compressor Stage ◽

Recovery Coefficient ◽

Vaned Diffuser ◽

Flow Angle ◽

Centrifugal Compressor Stage ◽

Numerical simulation of impeller and low solidity vaned diffuser (LSD) of a centrifugal compressor stage is performed individually using CFX- BladeGen and BladeGenPlus codes. The tip mach number for the chosen study was 0.35. The same configuration was used for experimental investigation for a comparative study. The LSD vane is formed using standard NACA profile with marginal modification at trailing edge. The performance parameters obtained form numerical studies at the exit of impeller and the diffuser have been compared with the corresponding experimental data. These parameters are pressure ratio, polytropic efficiency and flow angle at the impeller exit where as the parameters those have been compared at the exit of diffuser are the static pressure recovery coefficient and the exit flow angle. In addition, the numerical prediction of the blade loading in terms of blade surface pressure distribution on LSD vane has been compared with the corresponding experimental results. Static pressure recovery coefficient and flow angle at diffuser exit is seen to match closely at higher flows. The difference at lower flows could be due to the effect of interaction between impeller and diffuser combinations, as the numerical analysis was done separately for impeller and diffuser and the effect of impeller diffuser interaction was not considered.

A Preliminary Study of Annular Diffusers With Constant Diameter Outer Walls (Suitable for Turbine Exits)

Volume 1: Turbomachinery ◽

10.1115/83-gt-218 ◽

1983 ◽

Author(s):

R. C. Adkins ◽

O. H. Jacobsen ◽

P. Chevalier

Keyword(s):

Static Pressure ◽

Short Length ◽

Pressure Recovery ◽

Recovery Coefficient ◽

Constant Diameter ◽

Preliminary Study ◽

A systemmatic series of tests has been conducted on a family of annular diffusers where the outer casing is maintained at constant diameter. Such a diffuser is typical of turbine exits. Data, in the form of static pressure recovery coefficient is plotted against diffuser length for several different designs of centerbody closure. It has been shown that such diffusers can have short length centerbodies for which a set of design guides has been established.

Numerical Investigations on the Aerodynamic Performance of Last Stage – Exhaust Hood for Steam Turbines

ASME 2011 Power Conference, Volume 1 ◽

10.1115/power2011-55344 ◽

2011 ◽

Author(s):

Rui Yang ◽

Jiandao Yang ◽

Zeying Peng ◽

Liqun Shi ◽

Aping He ◽

...

Keyword(s):

Working Conditions ◽

Static Pressure ◽

Aerodynamic Performance ◽

Pressure Recovery ◽

Computational Domain ◽

Steam Turbines ◽

Exhaust Hood ◽

Recovery Coefficient ◽

Last Stage ◽

The aerodynamic performance and internal flow characteristics of the last stage and exhaust hood for steam turbines is numerically investigated using the Reynolds-Averaged Navier-Stokes (RANS) solutions based on the commercial CFD software ANSYS CFX. The full last stage including 66 stator blades and 64 rotor blades coupling with the exhaust hood is selected as the computational domain. The aerodynamic performance of last stage and static pressure recovery coefficient of exhaust hood at five different working conditions is conducted. The interaction between the last stage and exhaust hood is considered in this work. The effects of the non-uniform aerodynamic parameters along the rotor blade span on the static pressure recovery coefficient of the non-symmetric geometry of the exhaust hood are studied. The numerical results show that the efficiency of the last stage has the similar values ranges from 89.8% to 92.6% at different working conditions. In addition, the similar static pressure recovery coefficient of the exhaust hood was observed at five working conditions. The excellent aerodynamic performance of the exhaust hood was illustrated in this work.

Comparative Study on the Performance of S-Shaped Diffuser With Shorten Length

MATEC Web of Conferences ◽

10.1051/matecconf/201822505004 ◽

2018 ◽

Vol 225 ◽

pp. 05004

Author(s):

Raed A. Jessam ◽

Hussain H. Al-Kayiem ◽

Mohammad S. Nasif

Keyword(s):

Numerical Investigation ◽

Pressure Loss ◽

Static Pressure ◽

Cfd Simulation ◽

Pressure Coefficient ◽

Loss Coefficient ◽

Radius Of Curvature ◽

Recovery Coefficient ◽

Distortion Coefficient

This study presents numerical investigation on the performance of S-shaped air intake normal and aggressive diffuser with 22% length reduction. Both models have same area ratio of 3.1 with different total length, turning angle and radius of curvature. The numerical investigation was implemented using CFD simulation by ANSYS-FLUENT 15 software. The inlet Reynold number was 4×104 and turbulence intensity 4.1%. The performance evaluation was performed throw evaluation the static pressure coefficient, pressure loss coefficient, distortion coefficient and static pressure wall coefficient. The numerical results show that the performance in the case of aggressive S-shaped diffuser has been reduced compared to the normal S-shaped diffuser. This reduction resulting from the early flow separation and increase of the separation zone due to the high curvature of top and bottom surfaces of aggressive S-shaped diffuser. The results show that the static pressure recovery coefficient decreased by 31%, the total pressure loss coefficient and distortion coefficient increased by 9.5% and 8.2%, respectively, compared to the S-shaped diffuser. The static pressure wall coefficient on the top and bottom surfaces was dropped with the aggressive S-shaped diffuser.

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

Effects of struts profiles and skewed angles on the aerodynamic performance of gas turbine exhaust diffuser

10.1177/0957650920985201 ◽

2021 ◽

pp. 095765092098520

Author(s):

Yuxuan Dong ◽

Zhigang Li ◽

Jun Li ◽

Liming Song

Keyword(s):

Gas Turbine ◽

Static Pressure ◽

Three Dimensional ◽

Aerodynamic Performance ◽

Pressure Recovery ◽

Recovery Coefficient ◽

Flow Field Characteristics ◽

Gas Turbine Exhaust ◽

Pressure Recovery Coefficient ◽

Turbine Exhaust

The strut structure directly affects the flow field characteristics and aerodynamic performance of the gas turbine exhaust diffuser. The effects of the strut profiles and strut skewed angles on the aerodynamic performance of the exhaust diffuser at different inlet pre-swirls were numerically investigated using three-dimensional Reynolds-Averaged Navier-Stokes(RANS) and Realizable k-ε turbulence model. The numerical static pressure recovery coefficient of the exhaust diffuser is in agreement with the experimental data well. The reliability of the numerical method for the exhaust diffuser performance analysis was demonstrated. Exhaust diffusers with four kinds of vertical strut profiles obtain the highest static pressure recovery coefficient at the inlet pre-swirl of 0.35. The similar static pressure recovery coefficient of exhaust diffusers with four kinds of vertical strut airfoils are observed when the inlet pre-swirl is less than 0.48. The static pressure recovery coefficient of exhaust diffusers with vertical b1 and b2 struts are higher than that with the a1 and a2 struts when the inlet pre-swirl is greater than 0.48. At the inlet pre-swirl of 0.35, The static pressure recovery coefficient of the exhaust diffuser with the a1 strut decreases with the increasing of the strut skewed angles. The static pressure recovery coefficient of the exhaust diffuser with the b1 strut increases with the increasing of the strut skewed angles, and the static pressure recovery coefficient increases by 3.6% compared with the vertical design when the skewed angle of b1 strut is 40[Formula: see text]. At the inlet pre-swirl of 0.64. The static pressure recovery coefficient of the exhaust diffuser with the a1 strut increases by 8.7% compared with the vertical design when the skewed angle of a1 strut is greater than 20°. In addition, the static pressure recovery coefficient of the exhaust diffuser with the b1 strut decreases by 3.8% compared with the vertical design when the skewed angle of b1 strut is 40°. The method to improve the aerodynamic performance of the exhaust diffuser by appropriate increase the strut maximum thickness and design the strut skewed angle is proposed in this work.

Influence of Inlet Shape on Twin Intake Duct Performance

Volume 1: Turbo Expo 2005 ◽

10.1115/gt2005-68056 ◽

2005 ◽

Cited By ~ 1

Author(s):

K. Saha ◽

S. N. Singh ◽

V. Seshadri

Keyword(s):

Static Pressure ◽

Cross Flow ◽

Geometrical Parameters ◽

Recovery Coefficient ◽

Secondary Motion ◽

Vortical Motion ◽

Total Pressure Loss Coefficient ◽

Pressure Recovery Coefficient ◽

Oval Shape

Performance of twin intake ducts with different inlet shapes has been analyzed using a commercial CFD (Computational Fluid Dynamics) code. The performance has been evaluated for incompressible flow at a fixed Reynolds number (1.4×105). The shapes studied are rectangular (Aspect ratio = 2), square, semicircular, elliptic-1, elliptic-2 (inverse-elliptic) and oval shape with all the other geometrical parameters remaining same. The performance of the twin intake ducts in terms of the static pressure recovery coefficient, total pressure loss coefficient and distortion coefficient, and the secondary motion at the merging plane and the downstream planes show that the inverse elliptic shape is the best followed by semi-circular inlet. The vectors plots of secondary motion at the merging plane and downstream have shown the presence of twin pairs of vortical motion possibly caused by the change in centerline curvature. The cross flow vector plots also show four distinct vortices after merger.