Numerical Investigation of Effect of Blade Surface Slot on the Performance and Flow Field of a Low Speed Centrifugal Fan

2020 ◽  
Author(s):  
HaoGuang Zhang ◽  
FeiYang Dong ◽  
XuDong Zhang ◽  
WuLi Chu
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Flow Rate ◽  
Flow Condition ◽  
Low Energy ◽  
Centrifugal Fan ◽  
Blade Surface ◽  
Suction Surface ◽  
Flow Losses ◽  
Energy Flows

Abstract The main objective of this study is to understand the mechanisms of affecting the performance and flow field of a low speed centrifugal fan with blade surface slots. In the investigation, a spanwise slot, which is placed within the range of about 60% to 100% of the blade span, is applied to each blade surface of the impeller, and the partial blade pressure and suction surfaces for each blade are connected via the blade surface slot. The full-passage unsteady numerical results indicate that the performance of fan including the volute is improved among the overall mass flow rate by applying the blade surface slot, and the blade surface slots generate about an enhancement of 3.6% for the total pressure improvement, an improvement of 2.6% for the efficiency respectively at the design mass flow rate. The flow field analyses show that the injecting flows discharging from the blade surface slots can encourage the low energy flows near the blade suction surface in some blade passages. Hence, the boundary layer separations of the blade suction surface are restrained by the injecting flows, and the flow condition in the passag is considerately improved. Moreover, the adverse effect caused by the low energy flows is very serious in the partial blade passages near the shroud, while the flows in the blade surface slots have few positive effect on the low energy flows. So, the improvement by the slots on the flow fields is very small near the shroud region. Because the boundary layer separations on the blade suction surface are absent in most of the blade passages at about 60% of the blade span, the flows emerging from the slots have passive effects on the passage mainstreams. Further, in the case of blade surface slots, there is an obvious vortex near the blade trailing edge at about 60% of the blade span, and the vortex is close to the blade suction surface at some instants. As a result, the wake flow losses in the passage become large with the application of the slots. Briefly, within the slotted span range, the improvement of the flow field in the blade passages becomes large and then gets small, as the blade span decreases. Furthermore, the flow condition in the volute is improved thanks to the amelioration of the flows in some blade passages, and the degree of the second flows in the volute is weakened with the application of blade surface slots. Consequently, the flow losses in the volute are reduced effectively.

The Application of PIV in the Study of Impeller-Diffuser Interaction in Centrifugal Fan: Part I — Impeller-Vaneless Diffuser Interaction

2001 ◽  
Author(s):  
Tarek Mekhail ◽  
Zhang Li ◽  
Du Zhaohui ◽  
Willem Jansen ◽  
Chen Hanping
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
High Speed ◽  
Maximum Flow ◽  
Image Processing Technique ◽  
High Speed Photography ◽  
Centrifugal Fan ◽  
Performance Measurements ◽  
Vaneless Diffuser ◽  
Unstable Flow

Abstract The PIV (Particle Image Velocimetry) technology is a brand-new technique of measuring velocity. It started in the 1980’s with the development of high-speed photography and the image processing technique of computers. This article deals with PIV applied to the study of unsteady impeller-vaneless diffuser interaction in centrifugal fen. Experiments were carried out at The Turbomachinery Laboratory of Shanghai Jiaotong University. The test rig consists of a centrifugal, shrouded impeller, diffuser and volute casing all made of plexiglass. A series of performance measurements were carried out at different speeds and different vaneless diffuser widths. PIV measurements were applied to measure the unsteady flow at the exit part of the impeller and the inlet part of the diffuser for the case of the same width vaneless diffuser. The absolute flow field is measured at medium flow rate and at maximum flow rate. It is informative to capture the whole flow field at the same instant of time, and it might be more revealing to observe the unstable flow in real time.

Three-Dimensional Flow Field in Rocket Pump Inducers—Part 1: Measured Flow Field Inside the Rotating Blade Passage and at the Exit

1973 ◽  
Vol 95 (4) ◽  
pp. 567-578 ◽  
Author(s):  
B. Lakshminarayana
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Layer Growth ◽  
Surface Boundary ◽  
Suction Surface ◽  
Flow Losses ◽  
Rotating Blade ◽  
Order Of Magnitude ◽  
Measured Flow ◽  
Boundary Layer Growth

The measurement of the flow field within the rotating passages as well as three-dimensional characteristics of the exit flow of an inducer model is reported in this paper. The flow within the inducer is probed by means of rotating pitot probe and pressure transfer device and at the exit by means of three hot wires located in three coordinate directions. In a high solidity inducer (4 bladed), considerable boundary layer growth is observed from hub to mid radius, while the flow from mid radius to tip is found to be highly complex, due to interaction of pressure and suction surface boundary layers and the resulting radial inward flow. The flow losses and wall shear stress derived from these measurements are found to be considerably higher than the corresponding stationary channel. The radial velocities are found to be of the same order of magnitude as axial velocities. Considerable improvement in the flow field is observed when the number of blades is decreased from four to three.

scholarly journals Application of Vortex Generators in Flow Control of the Inlet

1985 ◽  
Author(s):  
Chen Xiao ◽  
Fang Liang-Wei
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Flow Separation ◽  
Dynamic Performance ◽  
Low Pressure ◽  
Transverse Flow ◽  
Vortex Generators ◽  
Flow Losses ◽  
Subsonic Diffuser ◽  
Selection Of

This paper introduces the features of using co-rotating vortex generators for controlling boundary layer and flow field in the inlet without flow separation. The principles of the arrangements of the blades and selection of constructional parameters of the generators that are applied to create the transverse flow between the high and low pressure regions and to reduce the secondary flow losses are analysed. The experimental results show that when the appropriate parameters of the co-rotating vortex generators are chosen for the inlet subsonic diffuser with apparent high and low pressure regions, not only the nonuniformity of the flow field is greatly improved but also the dynamic performance of the flow at exit is slightly improved.

scholarly journals Unsteady Characteristics of Forward Multi-Wing Centrifugal Fan at Low Flow Rate

Processes ◽  
2019 ◽  
Vol 7 (10) ◽  
pp. 691 ◽  
Author(s):  
Lun ◽  
Ye ◽  
Lin ◽  
Ying ◽  
Wei
Keyword(s):  
Unsteady Flow ◽  
Flow Rate ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Boundary Layer Separation ◽  
Low Flow ◽  
Centrifugal Fan ◽  
Suction Surface ◽  
Cfd Method ◽  
Low Flow Rate

The unsteady flow characteristics of a forward multi-wing centrifugal fan under a low flow rate are studied using the computational fluid dynamics (CFD) method. This paper emphasizes the eddy current distribution in terms of the Q criterion method, as well as pressure fluctuation, frequency spectrum, and kinetic energy spectrum analysis of internal monitoring points in a forward multi-wing centrifugal fan. The numerical results show that abnormal eddies mainly appear at the volute outlet and near the volute tongue, boundary layer separation occurs near the suction surface of the blade, and shedding eddies appear at the trailing edge of the blade with the time evolution. The unsteady flow characteristics of a forward multi-wing centrifugal fan at a small flow rate provide significant physical insight into understanding the internal flow law.

scholarly journals An Experimental Investigation Into the Reasons of Reducing Secondary Flow Losses by Using Leaned Blades in Rectangular Turbine Cascades With Incidence Angle

1988 ◽  
Author(s):  
Wang Zhongqi ◽  
Xu Wenyuan ◽  
Han Wanjin ◽  
Bai Jie
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Secondary Flow ◽  
Incidence Angle ◽  
Main Stream ◽  
Suction Surface ◽  
Flow Losses ◽  
Turbine Stator ◽  
Rear Part ◽  
Turbine Cascades

Up to now the reasons of reducing the secondary flow losses by using leaned blades, especially in the case of great incidence angle, have been little concerned with in published references. The experimental results in this paper have shown that the decisive factor reducing secondary flow losses in turbine stator cascades is the static pressure gradient along the blade height inside the cascade channel near the suction surface, especially in the rear part of it, because the negative pressure gradient in the hub region and the positive one in the tip region are beneficial for the boundary layer in both the regions to be sucked into the main stream region, consequently, the accumulation and the separation of the boundary layer have been weakened in both regions. Moreover, the effectiveness of applying the positively or negatively leaned blades is increased with the increase of a incidence angle, in the hub or the tip regions respectively.

The Influence of the Blading Surface Roughness on the Aerodynamic Behavior and Characteristic of an Axial Compressor

1980 ◽  
Vol 102 (2) ◽  
pp. 283-287 ◽  
Author(s):  
K. Bammert ◽  
G. U. Woelk
Keyword(s):  
Surface Roughness ◽  
Surface Quality ◽  
Flow Rate ◽  
Pressure Ratio ◽  
Axial Compressor ◽  
Low Flow ◽  
Blade Surface ◽  
Characteristic Curves ◽  
Flow Losses

The conversion of energy in an axial compressor is influenced in great measure by the surface quality of the blading. To achieve low flow losses, the roughness values of the blade surface must be below certain limits. However, the blade surface, which is hydraulically smooth on commissioning of the machine, is in many cases attacked by dirt, corrosion and erosion during operation. For investigation of the influence of the surface quality on the efficiency, flow rate, pressure ratio, and the shifting of the characteristic curves, systematic measurements were taken on a three-stage axial compressor with smooth and uniformly rough blading. The roughness was produced by applying loose emery grain of different grades.

Numerical analysis of a centrifugal fan for performance enhancement using boundary layer suction slots

2010 ◽  
Vol 224 (8) ◽  
pp. 1665-1678 ◽  
Author(s):  
K Vasudeva Karanth ◽  
N Yagnesh Sharma
Keyword(s):  
Boundary Layer ◽  
Static Pressure ◽  
Performance Enhancement ◽  
Radial Distance ◽  
Field Analysis ◽  
Pressure Recovery ◽  
Centrifugal Fan ◽  
Suction Surface ◽  
Impeller Blade ◽  
Boundary Layer Suction

Flow in centrifugal fans tends to be in a state of instability with flow separation zones on both the suction surface and the front shroud. The overall efficiency of the diffusion process in a centrifugal fan could be enhanced by judiciously introducing the boundary layer suction slots. With easy accessibility of computational fluid dynamics (CFD) as an analytical tool, an extensive numerical whole field analysis of the effect of boundary layer suction slots in discrete regions of suspected separation points is possible. This article attempts to explore the effect of boundary layer suction slots corresponding to various geometrical locations on the impeller as well as on the diffuser. The analysis shows that the suction slots located on the impeller blade near to its trailing edge appreciably improves the static pressure recovery across the fan. Slots provided at a radial distance of 30 per cent from the leading edge of the diffuser vane also significantly contribute to the static pressure recovery across the fan.

Unsteady Surface Pressures Due to Wake-Induced Transition in a Laminar Separation Bubble on a Low-Pressure Cascade

2004 ◽  
Vol 126 (4) ◽  
pp. 544-550 ◽  
Author(s):  
R. D. Stieger ◽  
David Hollis ◽  
H. P. Hodson
Keyword(s):  
Boundary Layer ◽  
Steady Flow ◽  
Coherent Structures ◽  
Separation Bubble ◽  
Pressure Fluctuations ◽  
Separation Point ◽  
Blade Surface ◽  
Suction Surface ◽  
Freestream Velocity ◽  
Wake Passing

This paper presents unsteady surface pressures measured on the suction surface of a LP turbine cascade that was subject to wake passing from a moving bar wake generator. The surface pressures measured under the laminar boundary layer upstream of the steady flow separation point were found to respond to the wake passing as expected from the kinematics of wake convection. In the region where a separation bubble formed in steady flow, the arrival of the convecting wake produced high frequency, short wavelength, fluctuations in the ensemble-averaged blade surface pressure. The peak-to-peak magnitude was 30% of the exit dynamic head. The existence of fluctuations in the ensemble averaged pressure traces indicates that they are deterministic and that they are produced by coherent structures. The onset of the pressure fluctuations was found to lie beneath the convecting wake and the fluctuations were found to convect along the blade surface at half of the local freestream velocity. Measurements performed with the boundary layer tripped ahead of the separation point showed no oscillations in the ensemble average pressure traces indicating that a separating boundary layer is necessary for the generation of the pressure fluctuations. The coherent structures responsible for the large-amplitude pressure fluctuations were identified using PIV to be vortices embedded in the boundary layer. It is proposed that these vortices form in the boundary layer as the wake passes over the inflexional velocity profiles of the separating boundary layer and that the rollup of the separated shear layer occurs by an inviscid Kelvin-Helmholtz mechanism.

Three-Dimensional Flow Field in the Tip Region of a Compressor Rotor Passage—Part I: Mean Velocity Profiles and Annulus Wall Boundary Layer

1982 ◽  
Vol 104 (4) ◽  
pp. 760-771 ◽  
Author(s):  
B. Lakshminarayana ◽  
M. Pouagare ◽  
R. Davino
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Three Dimensional ◽  
Leading Edge ◽  
Leakage Flow ◽  
Suction Surface ◽  
Mean Velocity ◽  
Wall Boundary Layer ◽  
Compressor Rotor ◽  
Wall Boundary

The flow field in the annulus wall and tip region of a compressor rotor was measured using a triaxial, hot-wire probe rotating with the rotor. The flow was surveyed across the entire passage at five axial locations (leading edge, 1/4 chord, 1/2 chord, 3/4 chord, and trailing edge locations) and at six radial locations inside the passage. The data derived include all three components of mean velocity. Blade-to-blade variations of the velocity components, pitch and yaw angles, as well as the passage-averaged mean properties of the annulus wall boundary layer, are derived from this data. The measurements indicate that the leakage flow starts beyond a quarter-chord and tends to roll up farther away from the suction surface than that observed in cascades. Substantial velocity deficiencies and radial inward velocities are observed in this region. The annulus wall boundary layer is well behaved up to half a chord, beyond which interactions with the leakage flow produce complex profiles.

The Measurement of Boundary Layers on a Compressor Blade in Cascade: Part 1—A Unique Experimental Facility

1987 ◽  
Vol 109 (4) ◽  
pp. 520-526 ◽  
Author(s):  
S. Deutsch ◽  
W. C. Zierke
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Pressure Distribution ◽  
Static Pressure ◽  
Compressor Blade ◽  
Boundary Layer Transition ◽  
Two Dimensional ◽  
Suction Surface ◽  
Pressure Surface ◽  
Static Pressure Distribution

A unique cascade facility is described which permits the use of laser-Doppler velocimetry (LDV) to measure blade boundary layer profiles. Because of the need for a laser access window, the facility cannot reply on continuous blade pack suction to achieve two-dimensional, periodic flow. Instead, a strong suction upstream of the blade pack is used in combination with tailboards to control the flow field. The distribution of the upstream suction is controlled through a complex baffling system. A periodic, two–dimensional flow field is achieved at a chord Reynolds number of 500,000 and an incidence angle of 5 deg on a highly loaded, double circular arc, compressor blade. Inlet and outlet flow profiles, taken using five-hole probes, and the blade static-pressure distribution are used to document the flow field for use with the LDV measurements (see Parts 2 and 3). Inlet turbulence intensity is measured, using a hot wire, to be 0.18 percent. The static-pressure distribution suggests both separated flow near the trailing edge of the suction surface and an initially laminar boundary layer profile near the leading edge of the pressure surface. Probe measurements are supplemented by sublimation surface visualization studies. The sublimation studies place boundary layer transition at 64.2 ± 3.9 percent chord on the pressure surface, and indicate separation on the suction surface at 65.6 percent ± 3.5 percent chord.

Sign in / Sign up

Export Citation Format

Share Document