Investigations Into the Flow Behavior in a Nonparallel Shrouded Diffuser of a Centrifugal Fan for Augmented Performance

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
N. Madhwesh ◽  
K. Vasudeva Karanth ◽  
N. Yagnesh Sharma
Keyword(s):  
Numerical Analysis ◽  
Static Pressure ◽  
Numerical Study ◽  
Flow Behavior ◽  
Pressure Rise ◽  
Radial Pressure ◽  
Vital Role ◽  
Centrifugal Fan ◽  
Energy Transformation ◽  
Pressure Equilibrium

It is a well-known fact that the diffuser of a centrifugal fan plays a vital role in the energy transformation leading to better static pressure rise and efficiency. Many researchers have worked on modified geometry with respect to both impeller and diffuser so as to extract better efficiency of the fan. This paper highlights a unique numerical study on the performance of a centrifugal fan, which has a diffuser having nonparallel shrouds. The shroud geometry is parametrically varied by adopting various convergence ratios (CR) for the nonparallel shrouds encompassing the diffuser passage. It is revealed in the study that there exists an optimal CR for which the performance is improved over the regular parallel shrouded diffuser passage (base model). It is observed from the numerical analysis that for a nonparallel convergent shroud corresponding to a CR of 0.35, a relatively higher head coefficient of 3.6% is obtained when compared to that of the base model. This configuration also yields a higher theoretical efficiency of about 2.1% corroborating the improvement in head coefficient. This study predicts a design prescription for nonparallel diffuser shrouds of a centrifugal fan for augmented performance due to the fact that the converging region accelerates and guides the flow efficiently by establishing radial pressure equilibrium.

Numerical investigations on the effect of volute casing treatment for performance augmentation in a centrifugal fan

2021 ◽  
pp. 095440622110341
Author(s):  
Manjunath L Nilugal ◽  
K Vasudeva Karanth ◽  
Madhwesh N
Keyword(s):  
Total Pressure ◽  
Static Pressure ◽  
Numerical Study ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Centrifugal Fan ◽  
Casing Treatment ◽  
Sliding Mesh ◽  
Optimum Configuration

This article presents the effect of volute chamfering on the performance of a forward swept centrifugal fan. The numerical analysis is performed to obtain the performance parameters such as static pressure rise coefficient and total pressure coefficient for various flow coefficients. The chamfer ratio for the volute is optimized parametrically by providing a chamfer on either side of the volute. The influence of the chamfer ratio on the three dimensional flow domain was investigated numerically. The simulation is carried out using Re-Normalisation Group (RNG) k-[Formula: see text] turbulence model. The transient simulation of the fan system is done using standard sliding mesh method available in Fluent. It is found from the analysis that, configuration with chamfer ratio of 4.4 is found be the optimum configuration in terms of better performance characteristics. On an average, this optimum configuration provides improvement of about 6.3% in static pressure rise coefficient when compared to the base model. This optimized chamfer configuration also gives a higher total pressure coefficient of about 3% validating the augmentation in static pressure rise coefficient with respect to the base model. Hence, this numerical study establishes the effectiveness of optimally providing volute chamfer on the overall performance improvement of forward bladed centrifugal fan.

Understanding the Flow Behavior in a Low Hub-Tip Ratio, High Aspect Ratio Contra-Rotating Axial Fan Stage

2012 ◽  
Author(s):  
Chetan S. Mistry ◽  
A. M. Pradeep
Keyword(s):  
Aspect Ratio ◽  
Total Pressure ◽  
Numerical Study ◽  
Flow Behavior ◽  
Experimental Studies ◽  
Pressure Rise ◽  
Operating Conditions ◽  
Speed Ratio ◽  
Axial Fan ◽  
Stall Margin

This paper discusses the results of a parametric study of a pair of contra-rotating axial fan rotors. The rotors were designed to deliver a mass flow of 6 kg/s at 2400 rpm. The blades were designed with a low hub-tip ratio of 0.35 and an aspect ratio of 3.0. Numerical and experimental studies were carried out on these contra-rotating rotors operating at a Reynolds number of 1.25 × 105 (based on blade chord). The axial spacing between the rotors was varied between 50 to 120 % of the chord of rotor 1. The performance of the rotors was evaluated at each of these spacing at design and off-design speeds. The results from the numerical study (using ANSYS CFX) were validated using experimental data. In spite of certain limitations of CFD under certain operating conditions, it was observed that the results agreed well with those from the experiments. The performance of the fan was evaluated based on the variations of total pressure, velocity components and flow angles at design and off-design operating conditions. The measurement of total pressure, flow angles etc. are taken upstream of the first rotor, between the two rotors and downstream of the second rotor. It was observed that the aerodynamics of the flow through a contra rotating stage is significantly influenced by the axial spacing between the rotors and the speed ratio of the rotors. With increasing speed ratios, the strong suction generated by the second rotor, improves the stage pressure rise and the stall margin. Lower axial spacing on the other hand, changes the flow incidence to the second rotor and thereby improves the overall performance of the stage. The performance is investigated at different speed ratios of the rotors at varying axial spacing.

Flow instability in a volute-free centrifugal fan subjected to non-axisymmetric pre-swirl flow from upstream bended inflow tube

2021 ◽  
pp. 095765092110626
Author(s):  
Zhengfeng Liu ◽  
Hui Yang ◽  
Haijiang He ◽  
Peiquan Yu ◽  
Yikun Wei ◽  
...  
Keyword(s):  
Static Pressure ◽  
Flow Instability ◽  
Pressure Fluctuations ◽  
Pressure Rise ◽  
Internal Flow ◽  
Temporal Variations ◽  
Swirl Flow ◽  
Incoming Flow ◽  
Centrifugal Fan ◽  
Local Flow

The characteristics of internal flow and performance of a centrifugal fan is greatly dependent on the inflow pattern. As the fan is subjected to incoming flow from an upstream tube, the size and geometry of the tube affect the three-dimensional motion of local flow and possibly degrades the aerodynamic performance of the fan. In this work, we performed a numerical investigation on the internal flow in a centrifugal fan subjected to incoming flow from an upstream bended inflow tube of various radii using the steady and unsteady Reynolds-averaged Navier-Stokes (RANS and URANS) simulation approaches. The effects of the non-axisymmetric pre-swirl flow generated due to the curvature of the bended inflow tube are demonstrated by analyzing the internal flow characteristics of the fan, including the spatial distributions and temporal variations of pressure field and streamlines, pressure fluctuations in the upstream tube, the inflow and outflow sections of the impeller, and the circumferential distributions of velocity and pressure in the impeller. The numerical results reveal that as the inflow tube is curved with larger curvature (smaller radius of the bended section), the pre-swirl inflow is strong and deteriorates the static pressure rise and static pressure efficiency of the centrifugal fan more remarkably, and the circumferential non-uniformity of pressure and velocity distributions appears inside of the channels of the fan. As the radius of the bended section increases, the instability of the internal flow gets more pronounced, as represented by the stronger pressure fluctuations at the inflow and outflow sections. The prediction capabilities of RANS and URANS approaches are also analyzed based on the numerical data and we found that the latter is more reliable in predicting the performance of the fan.

A NUMERICAL STUDY ON THE PERFORMANCE OF A SUDDEN EXPANSION WITH MULTISTEPS AS A DIFFUSER

2011 ◽  
Vol 03 (04) ◽  
pp. 779-802 ◽  
Author(s):  
D. K. MANDAL ◽  
N. K. MANNA ◽  
S. BANDYOPADHYAY ◽  
B. P. BISWAS ◽  
S. CHAKRABARTI
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Static Pressure ◽  
Numerical Study ◽  
Pressure Rise ◽  
Simple Algorithm ◽  
Stagnation Pressure ◽  
Effective Length ◽  
Sudden Expansion ◽  
Flow Reynolds Number

In this paper, the numerical analysis and performance simulation of a sudden expansion with multisteps viewed as a diffuser have been carried out. The two-dimensional steady differential equations for conservation of mass and momentum have been solved using the SIMPLE algorithm. The Reynolds number is in the range of 20 to 100. In this study, the configurations of plain sudden expansion and sudden expansion with two, three, four and five steps have been considered. An aspect ratio of 2 is fixed for all the computations. The effect of Reynolds number and number of steps on average static pressure, diffuser effectiveness, distance of maximum static pressure rise from throat and average stagnation pressure have been studied in detail. From the study, it is revealed that sudden expansion with multisteps always offers benefits in any Reynolds number (20–100) at aspect ratio of 2 with respect to a plain sudden expansion as far as its effectiveness and stagnation pressure drop are concerned. At lower Reynolds number, effectiveness of the sudden expansion with multisteps offers substantial benefit without much benefit in its performance at higher flow Reynolds number. The effective length of diffuser increases with Reynolds number, while, increase in number of steps does not have much impact on effective length at a particular value of flow Reynolds number.

scholarly journals Experimental investigations and empirical relationship on the influence of innovative hub geometry in a centrifugal fan for performance augmentation

2021 ◽  
Vol 16 (1) ◽  
Author(s):  
N. Madhwesh ◽  
K. Vasudeva Karanth ◽  
N. Yagnesh Sharma
Keyword(s):  
Fluid Flow ◽  
Flow Behavior ◽  
Empirical Relationship ◽  
Vital Role ◽  
Experimental Investigations ◽  
Centrifugal Fan ◽  
Centrifugal Fans ◽  
Main Components ◽  
The Cost ◽  
Shape And Size

Abstract Background One of the problem areas of fluid flow in the turbomachine is its inlet region, manifested by flow distortions due to the induced fluid swirl accompanied by improper flow incidence onto the impeller. Further, the hub forms one of the main components of many of the turbomachines and it is found that there has not been significant study on geometrical modifications of the same in centrifugal fans for augmented performance. This is partially due to designers trying to reduce the cost of the overall machine. Objective There is a scope for detailed parametric study and the present work involves an exploration of flow behavior by parametric variation of hub geometry in terms of both its shape and size. Methods Experiments are carried out in order to determine the importance of hub with different size and shapes. The geometric models of hemi-spherical and ellipsoidal hubs are considered for the analyses in the present study. Results An optimized ellipsoidal hub configuration is found to yield a relative improvement of about 7.5% for head coefficient and 7.7% increase in relative theoretical efficiency over the hub-less base configuration. Finally, correlations are developed for the optimized hub shape configurations. Conclusion It is revealed from experimental analysis that hub plays a vital role in streamlining the flow at the inlet to the centrifugal fan and augments its performance.

Enhancement of Flow Diffusion in a Centrifugal Compressor Stage with Backward Curved Impeller by Shroud Extension – A Numerical Study

2014 ◽  
Vol 984-985 ◽  
pp. 1102-1107 ◽  
Author(s):  
Sivamani Seralathan ◽  
D.G. Roy Chowdhury ◽  
Anil Kumar Jaswal
Keyword(s):  
Centrifugal Compressor ◽  
Static Pressure ◽  
Numerical Study ◽  
Pressure Rise ◽  
Centrifugal Impeller ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Centrifugal Compressor Stage ◽  
Side Walls

Efficient, compact centrifugal compressor with higher pressure ratios along with adequate surge margins necessitates developing non-conventional diffuser designs. A method of reducing shear losses on the stationary vaneless diffuser sidewalls is by rotating the side walls of vaneless diffuser. Forced rotating vaneless diffuser, a type in which the diffuser is integral with impeller and rotates at same speed, is obtained by extending the impeller disks beyond the blades. In this paper, the conventional stationary vaneless diffuser is redesigned to act as a ‘forced’ rotating vaneless diffuser. The effect of shroud extension is analyzed for the backward curved centrifugal impeller with shrouds extended by 40% with impeller exit diameter on flow diffusion and compared to an impeller with stationary vaneless diffuser. A higher static pressure rise by around 10% along with reduced losses is achieved by shroud extension configuration, RVD-ES. This indicates that the rate of diffusion is higher in the extended shroud configuration.

Elastic Turbulence Effects on the Performance of a Miniature Viscous Disk Pump

2015 ◽  
Author(s):  
Benjamin Lund ◽  
Maria Brown ◽  
Mary Jennerjohn ◽  
Phil Ligrani ◽  
Arshia Fatemi
Keyword(s):  
Rotational Speed ◽  
Static Pressure ◽  
Flow Behavior ◽  
Pressure Rise ◽  
Weissenberg Number ◽  
Physical Processes ◽  
Channel Depth ◽  
Fundamental Understanding ◽  
Turbulence Effects ◽  
Strain Increase

Within the present investigation, a miniature viscous disk pump (VDP) is utilized to characterize and quantify non-Newtonian fluid elastic turbulence effects, relative to Newtonian flow behavior. Such deviations from Newtonian behavior are induced by adding polyacrylamide to purified water. The VDP consists of a 10.16 mm diameter disk that rotates above a C-shaped channel with inner and outer radii of 1.19 mm, and 2.38 mm, respectively. A channel depth of 230 μm is employed. Fluid inlet and outlet ports are located at the ends of the C-shaped channel. Within the present study, experimental data are given for rotational speeds of 1200–3500 rpm, pressure rises of 0 to 700 Pa, and flow rates up to approximately 0.00000007 m3/sec. As such, the overall intent is enhancement of fundamental understanding of the associated physical processes associated with elastic turbulence, as it is induced in liquids by polymers subject to stretching and constriction by flow strain. Different amounts of flow strain are induced by changing the rotational speed of the disc. As rotational speed increases, overall magnitudes of flow strain increase, and the polymer strings become locally more agitated. The result is growth in the local elastic stress, and development of the Weissenberg instability as the Weissenberg number increases. Overall consequences include increased mixing, increased transport levels, and larger static pressure rise magnitudes. Also considered are changes to effective viscosity from the presence of elastic turbulence.

Effects of Downstream Stator Pressure Field on Upstream Rotor Performance

1996 ◽  
Author(s):  
Martin B. Graf ◽  
Om P. Sharma
Keyword(s):  
Boundary Condition ◽  
Static Pressure ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Radial Pressure ◽  
Pressure Profile ◽  
Inviscid Flow ◽  
Tip Clearance ◽  
Radial Profiles ◽  
Rotor Loss

Results of numerical simulations conducted for a high pressure compressor rotor with two different levels of tip clearance are presented. A three-dimensional, steady, Reynolds-Averaged Navier-Stokes code was utilized to perform the computations. The simulations were executed over a range of flow coefficients by specifying different axisymmetric radial profiles in static pressure downstream of the rotor. In this manner, the effect of the downstream stator row was approximated using a simple, circumferentially averaged, radial pressure profile as the boundary condition behind the rotor. The back pressure profiles utilized were those deduced from inviscid flow computations for two different stator designs: (1) a conventional radial stator, and (2) a three-dimensional “bowed” stator. Results of the rotor simulations with nominal tip clearance show that the boundary condition induced by the bowed stator causes a 2% decrease in rotor pressure rise capability, and a 9% increase in rotor loss as compared with the conventional stator. In addition, as the tip clearance is increased to twice the nominal value, the rotor loss grows at a rate 25% higher for the rotor subjected to the bowed stator pressure profile. Accompanying this is a dramatic reduction in rotor speedline slope and pressure rise capability. Analysis of the simulations shows these effects to be linked to the response of the rotor tip clearance vortex to the exit pressure profile set by the downstream stator. These results indicate the need to accurately model the effects of the radial variation in static pressure imposed by the downstream airfoil rows.

Outlet Surface Area Influence in Spiral Casing Design on Centrifugal Fan Performance

2020 ◽  
Vol 5 (1) ◽  
pp. 37-41
Author(s):  
Ardit Gjeta ◽  
Lorenc Malka
Keyword(s):  
Surface Area ◽  
Static Pressure ◽  
Total Efficiency ◽  
Centrifugal Fan ◽  
Recovery Coefficient ◽  
Fan Performance ◽  
Parameter Variations ◽  
Set Up ◽  
Spiral Casing ◽  
Pressure Recovery Coefficient

In this paper, the effect of the outlet surface area of the spiral casing on the performance of a centrifugal fan was investigated using open source CFD software OpenFOAM [1]. An automized loop with RANS and data post-processing is set up using Matlab, for allowing a large number of parameter variations. The effect was analyzed as a function of total pressure loss and static pressure recovery coefficient and on total efficiency as well.

NUMERICAL ANALYSIS OF FLOW BEHAVIOR AND INFLUENCE OF THE REAR SLOPE ANGLE IN AN AHMED’S BODY

2020 ◽  
Author(s):  
Bernardo Silva da Rocha ◽  
charles rech ◽  
Maikson Luiz Passaia Tonatto
Keyword(s):  
Numerical Analysis ◽  
Flow Behavior ◽  
Slope Angle
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