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.

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.

Calculation of Aerodynamic Noise for Centrifugal Fan of Air-Conditioner

2013 ◽  
Author(s):  
Taku Iwase ◽  
Hideshi Obara ◽  
Hiroyasu Yoneyama ◽  
Yoshinobu Yamade ◽  
Chisachi Kato
Keyword(s):  
Sound Pressure ◽  
Static Pressure ◽  
Pressure Fluctuations ◽  
Coarse Grid ◽  
Aerodynamic Noise ◽  
Absolute Velocity ◽  
Centrifugal Fan ◽  
Air Conditioner ◽  
Simulation Code ◽  
Fine Grid

Flow fields in a centrifugal fan for an indoor unit of an air-conditioner were calculated with finite element method-based large eddy simulation (LES) with the aim of predicting fan performance and aerodynamic noise in this study. The numerical simulation code employed throughout the LES was called FrontFlow/blue (FFB). We compared 10M grid [coarse grid] and 60M grid [fine grid] calculation results for investigation of influence of grid resolution. In the fine grid, the number of grid elements in blade-to-blade direction, and of region between the shroud and the bell mouth increased in particular. By calculating with the fine grid, calculated distributions of absolute velocities at blade exit reasonably agreed with experimental results. Because of this, maximum absolute velocity by fine grid near hub decreased as compared to those by coarse grid. Calculated sound pressure level by fine grid was therefore smaller than that by coarse grid, and the overestimation of sound pressure was suppressed by calculating with fine grid. This decrease of the absolute velocity was a first factor for the improvement of calculation accuracy. Moreover, number of captured streaks on the blade, hub, and shroud surfaces by fine grid increased as compared to those by coarse grid. As a result, size of streak by fine grid became smaller than that by coarse grid. Static pressure fluctuations by fine grid on the blade, hub, and shroud surfaces therefore reduced as compared to those by coarse grid. Aerodynamic noise was related to static pressure fluctuations according to Curle’s equation. This reduction of static pressure fluctuations was therefore a second factor for improvement of calculation accuracy.

2D and 3D Unsteady Flow in Squirrel-Cage Centrifugal Fan and Aeroacoustic Behavior

2006 ◽  
Author(s):  
M. Younsi ◽  
F. Bakir ◽  
S. Kouidri ◽  
R. Rey
Keyword(s):  
Unsteady Flow ◽  
Numerical Models ◽  
Pressure Fluctuations ◽  
Internal Flow ◽  
Navier Stokes ◽  
Computational Domain ◽  
Centrifugal Fan ◽  
Geometry Modeling ◽  
3D Unsteady Flow ◽  
2D And 3D

The objective of this paper is the study and the analysis of the complex phenomena related to the internal flow in a centrifugal fan, using Computational Fluid Dynamics (CFD) tools, completed with experimental investigation in order to validate the used numerical models. The CFD analysis concerns 2D and 3D unsteady flow. The studied phenomena are the interactions and unsteadiness induced by the motion of the rotating blades relatively to the volute and their impact on the aeroacoustic behavior of the fan. Thus, 3D and 2D unsteady calculations using Unsteady Reynolds Averaged Navier Stokes (URANS) approach has been applied on a hybrid mesh grid whose refinement has been studied and adapted to the flow morphology. Turbulence has been modeled with the k-ω-Shear Stress Model (SST) model. The computational domain has been divided into two zones, a rotating zone including the impeller and stationary zone including the volute. A sliding mesh technique has been applied to the interfaces in order to allow the unsteady interactions between the two zones. The overall performances predicted by the computations have been validated at different flow rate. For each geometry modeling (2D and 3D), the unsteady part of the study is illustrated by analyzing the pressure fluctuations on different points from the lateral surface of the volute. The analysis of the wake generated by the rotation of the blower shows that the volute tongue is the main zone of unsteadiness and flow perturbations. In order to predict the acoustic pressures, the unsteady flow field variables provided by the CFD calculations have been used as inputs in the Ffowks Williams-Hawkings equations.

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.

Unstable Characteristics and Rotating Stall in Turbine Brake Operation of Pump-Turbines

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Christian Widmer ◽  
Thomas Staubli ◽  
Nathan Ledergerber
Keyword(s):  
Electricity Market ◽  
Flow Instability ◽  
Guide Vane ◽  
Pressure Fluctuations ◽  
Vortex Formation ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Momentum Exchange ◽  
Pump Turbine ◽  
Stationary Vortex

Reversible pump-turbines are versatile in the electricity market since they can be switched between pump and turbine operation within a few minutes. The emphasis on the design of the more sensitive pump flow however often leads to stability problems in no load or turbine brake operation. Unstable characteristics can be responsible for hydraulic system oscillations in these operating points. The cause of the unstable characteristics can be found in the blocking effect of either stationary vortex formation or rotating stall. The so-called unstable characteristic in turbine brake operation is defined by the change of sign of the slope of the head curve. This change of sign or “S-shape” can be traced back to flow recirculation and vortex formation within the runner and the vaneless space between runner and guide vanes. When approaching part load from sound turbine flow the vortices initially develop and collapse again. This unsteady vortex formation induces periodical pressure fluctuations. In the turbine brake operation at small guide vane openings the vortices increase in intensity, stabilize and circumferentially block the flow passages. This stationary vortex formation is associated with a total pressure rise over the machine and leads to the slope change of the characteristic. Rotating stall is a flow instability which extends from the runner, the vaneless space to the guide and the stay vane channels at large guide vane openings. A certain number of channels is blocked (rotating stall cell) while the other channels comprise sound flow. Due to a momentum exchange between rotor and stator at the front and the rear cell boundary, the cell is rotating with subsynchronous frequency of about 60 percent of the rotational speed for the investigated pump-turbine (nq = 45). The enforced rotating pressure distributions in the vaneless space lead to large dynamic radial forces on the runner. The mechanisms leading to stationary vortex formation and rotating stall were analyzed with a pump-turbine model by the means of numerical simulations and test rig measurements. It was found that stationary vortex formation and rotating stall have initially the same physical cause, but it depends on the mean convective acceleration within the guide vane channels, whether the vortex formations will rotate or not. Both phenomena lead to an unstable characteristic.

Effects of vortex structure on performance characteristics of a multiblade fan with inclined tongue

2019 ◽  
Vol 233 (8) ◽  
pp. 1007-1021 ◽  
Author(s):  
Yuxin Lun ◽  
Limin Lin ◽  
Haijiang He ◽  
Xinxue Ye ◽  
Zuchao Zhu ◽  
...  
Keyword(s):  
Quantitative Analysis ◽  
Vortex Structure ◽  
Static Pressure ◽  
Internal Flow ◽  
Centrifugal Fan ◽  
Q Value ◽  
Flow Loss ◽  
And Performance ◽  
Insight Into ◽  
Original Configuration

The effects of complex vortex structure on the internal flow and performance of a centrifugal fan with inclining symmetrical volute tongue were investigated by numerical simulations. The comparison between experimental results and numerical results on performance of a centrifugal fan is presented. To provide a quantitative analysis on the vortex structure in the internal flow of fan, Q criterion as a rule of vortex decision is implemented. Effects on vortex structure and X-velocity of the volute outlet are analyzed by modifying clearance and radius. It is analyzed to provide insight into the performance of the centrifugal fan. Special attention is devoted to the influence of the static pressure and efficiency of the fan by increasing radius of the volute tongue, changing tongue clearance and inclining volute tongue in this paper. The results also show that the static pressure of model B rises as much as 10.59 Pa and the efficiency can be improved by more than 4% compared with the original configuration due to the reduction of flow loss. It is further found that the static pressure efficiency increases with decreasing Q value distribution in the internal flow of the fan.

The Optimal Research on Impeller Central Location of Centrifugal Fan

2014 ◽  
Vol 668-669 ◽  
pp. 729-732
Author(s):  
Yu Kun Lv ◽  
Bo Zhang ◽  
Bo Cheng
Keyword(s):  
Flow Field ◽  
Static Pressure ◽  
Internal Flow ◽  
Flow Fields ◽  
Centrifugal Fan ◽  
Contrastive Analysis ◽  
Location Optimization ◽  
Central Location ◽  
Center Location ◽  
Variable Condition

Taking the G4-73№8D centrifugal fan as research object and utilizing the software of NUMECA to simulate flow fields of volutes with different radial relative positions, the optimum central location of the fan impeller was obtained. The contrastive analysis of internal flow field which of the original and impeller center location optimization fan was under the rated and variable condition, showed that the optimized fan enhanced impeller and volute casing radial adaptive and the efficiency and export static pressure of optimized fan were improved.

Performance Degradation and Flow Instability of Axial-Flow Fan Due to Upstream Obstacle

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Donghyuk Kang ◽  
Takeru Shinohara ◽  
Shinsaku Nakamura ◽  
Koichi Nishibe ◽  
Kotaro Sato ◽  
...  
Keyword(s):  
Pressure Loss ◽  
Flow Instability ◽  
Flow Direction ◽  
Axial Flow ◽  
Swirl Flow ◽  
Performance Degradation ◽  
Low Flow ◽  
Power Coefficient ◽  
Centrifugal Fan ◽  
Axial Fan

Abstract This paper elucidates the performance degradation and flow instability of an axial fan caused by the presence of disk-shaped obstacles upstream of the fan, such as wall surfaces. The increase in pressure loss and the decrease in shaft power coefficient due to inlet swirl flow, and the increase in pressure loss due to the outlet swirl flow, cause performance degradation. When the obstacle is closer to the fan, the strong swirl flow causes a negative pressure region between the fan and the obstacle, reversing the flow direction. This phenomenon is caused by the diffuser effect of the outward flow and the increase in pressure by acting as a multiblade centrifugal fan. At a low flow rate, a clockwise vortex is generated at the center of the obstacle and induces two counterclockwise rotating vortices. The vortices circumferentially separate the inward and outward flows along the fan's axis in a uniform manner, and their cores are circularly rotated by the clockwise vortex. These findings can contribute to the layout of fans under spatial restriction and suppression of flow instability due to obstacles.

Suppression of Diffuser Rotating Stall in a Centrifugal Pump by Use of Slit Vane

2021 ◽  
Author(s):  
Shunya Takao ◽  
Shinichi Konno ◽  
Shinichiro Ejiri ◽  
Masahiro Miyabe
Keyword(s):  
Flow Rate ◽  
Static Pressure ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Time History ◽  
Internal Flow ◽  
Rotating Stall ◽  
The Other ◽  
Wave Form ◽  
Other Hand

Abstract The objective of this research is to suppress pressure fluctuation by machining slits to the diffuser vanes and clarify its effect on the diffuser rotating stall from the hydrodynamics point of view. In order to investigate pressure fluctuations due to the diffuser rotating stall, both experiment and CFD (Computational Fluid Dynamics) calculations were conducted. In the experiment, two kinds of pump (one is original and another is with slit vanes) characteristics and time history of static pressure were measured. Then, data processing of wave form were conducted by FFT (Fast Fourier Transform) analysis. The static pressure transducers were mounted at casing-side of diffuser inlet in two passages. On the other hand, the CFD calculations were carried out to investigate the behavior of the diffuser rotating stall and the effect of slit vanes using a commercial CFD software, ANSYS CFX. A positive slope of head-flow characteristics is confirmed around at ϕ = 0.036 in the case of original pump. On the other hand, it has been shifted to lower flow rate, ϕ = 0.020 in the case of slit vanes. The periodic pressure fluctuations were observed for both cases at those flow rate, respectively. Then, it was confirmed that the diffuser rotating stall occurs and the number of cell is one from the co-relation between pressure wave form of two flow passages. The unsteady RANS (Reynolds-averaged Navier-Stokes) calculations were conducted for two kinds of pump. Then the internal flow within the diffuser were compared and the differences were clarified.

Computational Estimation of Fan Casing Noise at Blade Passing Frequency Component Noise

2012 ◽  
Vol 184-185 ◽  
pp. 95-100
Author(s):  
Jian Cheng Cai ◽  
Yong Hai Zhang ◽  
Shuang Li Long
Keyword(s):  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
Sound Radiation ◽  
Internal Flow ◽  
Neumann Boundary ◽  
Frequency Component ◽  
Dipole Source ◽  
Centrifugal Fan ◽  
Element Analysis ◽  
Blade Passing Frequency

This paper studies both vibroacoustics and aeroacoustics of a centrifugal fan casing; the aim of this study is to explore a methodology to make quantitative predictions of fan casing noise. The spectra of the fan noise and casing vibration were firstly presented; discrete components related to the rotational frequency protrude in the spectra, especially the blade passing frequency (BPF). Computational fluid dynamics (CFD) technique was used to obtain the three-dimensional unsteady turbulent internal flow. Attention was paid to the pressure fluctuations on the volute wall; the shapes of pressure fluctuation were nearly sinusoidal in nature, with the BPF as the primary frequency. On the vibroacoustic side, Fast Fourier Transform (FFT) was applied to the time series of pressure fluctuations to extract the BPF component. A finite element analysis (FEA) model of the casing structure was constructed, and was validated by experimental modal analysis. The harmonic dynamic response of the casing structure was calculated with the BPF pressure fluctuation component as the excitation. The vibration results were then taken as the velocity (Neumann) boundary condition for the noise radiation model which was built in boundary element method (BEM), and the sound radiation was calculated. On the aeroacoustic side, the BPF component of pressure fluctuations was modeled as acoustic dipole source, and sound radiation was also solved by BEM. Results show that the sound pressure level (SPL) of vibroacoustics is fairly small compared to the aeroacoustic counterpart. This study shows that CFD, FEA together with BEM can be used to numerically predict BPF casing noise of turbomachinery successfully.

Sign in / Sign up

Export Citation Format

Share Document