Experimental Study of the Effect of Serrations on Axial Flow Fan Blade Trailing Edge

2016 ◽  
Author(s):  
Dhyanjyoti Deb Nath ◽  
K. Viswanath ◽  
Ankit Bhai Patel
Keyword(s):  
Axial Velocity ◽  
Pressure Sensors ◽  
Tangential Velocity ◽  
Axial Flow ◽  
Experimental Investigations ◽  
Spanwise Direction ◽  
Axial Fan ◽  
Trailing Edge ◽  
Trailing Edges ◽  
Fan Blade

Rotor wakes shed from a compressor rotor impinge on downstream blades and is a major source of rotor-stator interaction noise and much research has been dedicated on wake attenuation. Serrated trailing edges is one such wake attenuation technique where the vortices produced at the serrated trailing edges enhance mixing and create a more uniform flow at stator inlet. The present paper investigates the effect of serrations on the trailing edge of a forced vortex axial fan blade. Experimental investigations were carried out at rotor outlet using pneumatic probes and fast response pressure sensors. It is found that total and static pressures reduce in serrated blades due to reduced turning and hence reduced work input. The absolute tangential velocity wake deficit decreases in serration valleys and improvement in axial velocity wake deficit is also found. Improvements as large as 19% and 18% decrease in absolute tangential velocity and axial velocity wake deficit are found at certain radii. The spanwise shape of the wake is altered by the serrations and a wake pattern undulating in the spanwise direction is observed. These are expected to bring down the circumferential variation of the velocity and its phase before entering the next row of blades and bring down the tonal noise.

scholarly journals Prediction of noise from serrated trailing edges

2016 ◽  
Vol 793 ◽  
pp. 556-588 ◽  
Author(s):  
B. Lyu ◽  
M. Azarpeyvand ◽  
S. Sinayoko
Keyword(s):  
Noise Reduction ◽  
Analytical Model ◽  
Leading Edge ◽  
Experimental Investigations ◽  
Destructive Interference ◽  
Trailing Edge ◽  
Trailing Edges ◽  
Mach Numbers ◽  
Trailing Edge Serrations ◽  
High Mach

A new analytical model is developed for the prediction of noise from serrated trailing edges. The model generalizes Amiet’s trailing-edge noise theory to sawtooth trailing edges, resulting in a complicated partial differential equation. The equation is then solved by means of a Fourier expansion technique combined with an iterative procedure. The solution is validated through comparison with the finite element method for a variety of serrations at different Mach numbers. The results obtained using the new model predict noise reduction of up to 10 dB at 90$^{\circ }$ above the trailing edge, which is more realistic than predictions based on Howe’s model and also more consistent with experimental observations. A thorough analytical and numerical analysis of the physical mechanism is carried out and suggests that the noise reduction due to serration originates primarily from interference effects near the trailing edge. A closer inspection of the proposed mathematical model has led to the development of two criteria for the effectiveness of the trailing-edge serrations, consistent but more general than those proposed by Howe. While experimental investigations often focus on noise reduction at 90$^{\circ }$ above the trailing edge, the new analytical model shows that the destructive interference scattering effects due to the serrations cause significant noise reduction at large polar angles, near the leading edge. It has also been observed that serrations can significantly change the directivity characteristics of the aerofoil at high frequencies and even lead to noise increase at high Mach numbers.

Aerodynamic and Acoustic Performance of a Single Stage Axial Fan With Extensive Blade Sweep Designed to Limit Noise Emissions

2016 ◽  
Author(s):  
Daniel Giesecke ◽  
Jens Friedrichs ◽  
Udo Stark ◽  
Maik Dierks
Keyword(s):  
Axial Flow ◽  
Leading Edge ◽  
Vital Role ◽  
Single Stage ◽  
Numerical Verification ◽  
Axial Fan ◽  
Trailing Edge ◽  
Sweep Angle ◽  
Acoustic Performance ◽  
Versatile Tool

Not only the aerodynamic performance of axial flow fans is important but also the acoustic behaviour plays a vital role. It is to be expected that in the future noise limits will be more regulated by legislation. The aim of this project is to develop a very versatile tool for efficient and noise reduced axial flow fans in rotor / stator configuration. This paper describes the design, numerical verification and tests of a highly loaded single stage axial flow fan making use of extensive blade sweep in rotor and stator for acoustic reasons. The tests include aerodynamic and acoustic investigations. The stage is a conventional free vortex design with unconventional blades of a special planform. The blade sections of both rotor and stator are NACA 65-sections on circular arc mean lines. Sectional diffusion factors and de Haller numbers are close to their respective limits, especially for the sections next to the rotor and stator hubs. The rotor is characterised by a forward-swept leading edge with increasing sweep angle towards hub and tip and an unswept trailing edge. The leading edge of the stator blades is forward-swept as before but this time at an almost constant sweep angle between the hub and the two-thirds position of the blade span. The trailing edge is straightened for reducing the previously mentioned aerodynamic loadings. The study shows that the numerical results are consistent with the experimental outcome. It concludes that the advanced design features show potential aerodynamic and acoustic benefits by sweeping the blade in the described manner. This is particularly the case when comparing to single row designs.

Parmeterization of the Total Pressure Distribution Along a Low-Pressure Axial Fan Blade According to the Design Requirements

2008 ◽  
Author(s):  
Maria Pascu ◽  
Philipp Epple ◽  
Antonio Delgado ◽  
Franz Durst
Keyword(s):  
Total Pressure ◽  
Design Method ◽  
Flow Characteristics ◽  
Axial Flow ◽  
Critical Parameters ◽  
Design Strategies ◽  
Axial Fan ◽  
Absolute Increase ◽  
Overall Performance ◽  
Fan Blade

In the field of axial flow turbomachines, the two–dimensional cascade model is often used experimentally or numerically to investigate fundamental flow characteristics and overall performance of the impeller. The core of the present work is a design method for axial fan cascades aiming to derive inversely the optimum blade shape based on the requirements of the impeller and not using any predefined airfoil profiles. While most design strategies based on the airfoil theory assume constant total pressure at all streamlines, i.e. free–vortex flow, this paper investigates the possibility of varying the total pressure along the blade and based on that, an analytical expression of the outlet blade angle is determined. When computing the blade profile at specified radius, critical parameters reflecting on the flow characteristics are observed and adjusted, i.e. sufficient lift and controlled deceleration of the flow on the contour so that the resulting profile is derived for minimum losses. The validation of this design strategy is given by the numerical results obtained when employed as an optimization tool for an industrial fan: 10–20% absolute increase in the efficiency of the optimized impeller.

scholarly journals Investigations on noise sources on a contra-rotating axial fan with different modifications

2019 ◽  
Vol 111 ◽  
pp. 02076 ◽  
Author(s):  
Ralph Krause ◽  
Christian Friebe ◽  
Michael Kerscher ◽  
Christof Puhle
Keyword(s):  
Axial Fan ◽  
Noise Sources ◽  
Trailing Edge ◽  
Sound Sources ◽  
Rotating Blades ◽  
First Results ◽  
Fan Blade ◽  
Future Work ◽  
Different Sources ◽  
Beamforming Algorithm

An Acoustic Camera was applied to examine modifications of fan blade designs regarding their noise emissions. A so-called rotational beamforming algorithm allows for the detection of sound sources on the rotating blades by using a virtual rotation of the microphones. Depending upon the frequency different sources could be localized. Both the leading and the trailing edge were modified. This paper shows the performed modifications and tests with the Acoustic Camera. It also presents first results and gives an outlook on future work.

The Stability of Viscous Axial Flow in the Entry Region of an Annulus with a Rotating Inner Cylinder

1976 ◽  
Vol 18 (5) ◽  
pp. 221-228 ◽  
Author(s):  
B. W. Martin ◽  
M. A. Hasoon
Keyword(s):  
Reynolds Number ◽  
Axial Length ◽  
Axial Velocity ◽  
Tangential Velocity ◽  
Axial Flow ◽  
Radius Ratio ◽  
Neutral Stability ◽  
Hot Wire ◽  
Core Rotation ◽  
The Stability

The stability of developing tangential flow induced by the imposition of an axial velocity on the tangential velocity distribution created by core rotation is theoretically and experimentally investigated. A linear stability analysis is used to examine the influence of axial length, axial Reynolds number and annulus radius ratio on the critical Taylor number for neutral stability when the axial velocity is assumed uniform. Predictions compare favourably with measurements obtained by hot-wire anemometer for air flowing in an annulus of radius ratio 0·9, particularly at small Reynolds number and large values of the axial length parameter.

Influence on the Axial Flow Fan Aerodynamic Characteristic Due to an Introduction of Internal Secondary Flow

2008 ◽  
Author(s):  
Matjazˇ Eberlinc ◽  
Brane Sˇirok ◽  
Marko Hocˇevar ◽  
Matevzˇ Dular
Keyword(s):  
Standardized Test ◽  
Flow Direction ◽  
Axial Flow ◽  
Performance Testing ◽  
Internal Flow ◽  
Suction Side ◽  
Flow Conditions ◽  
Axial Fan ◽  
Trailing Edge ◽  
Local Characteristics

Axial fans often show adverse flow conditions at the fan hub and at the tip of the blades. Modification of conventional axial fan blades is presented. Hollow blades were manufactured from the hub to the trailing edge at the tip of the blades. Hollow blades enabled the formation of self-induced internal flow through internal passages. The internal flow enters the internal radial flow passages of the hollow blades through the openings near the fan hub and exits through the tip trailing edge slots. Study of the influence of internal flow on the flow field of axial fan and modifications of axial fan aerodynamic characteristics is presented. The characteristics of the axial fan with the internal flow were compared to characteristics of a geometrically equivalent fan without internal flow. The results show integral measurements of performance testing using standardized test rig, and the measurements of local characteristics. The measurements of local characteristics were performed with a hot-wire anemometry, five-hole probe and computer-aided visualization. We attained reduction of adverse flow conditions near the blade tip trailing edge, boundary-layer reduction on the blade suction side and reduction of flow separation. Introduction of the self-induced blowing led to the preservation of external flow direction, defined by blade geometry and enabled maximal local energy conversion. The integral characteristic reached higher degree of efficiency.

A Simple Method for the Selection of Axial Fan Blade Profiles

1978 ◽  
Vol 192 (1) ◽  
pp. 269-275 ◽  
Author(s):  
N. Hay ◽  
R. Metcalfe ◽  
J. A. Reizes
Keyword(s):  
Design Method ◽  
Axial Flow ◽  
Operating Conditions ◽  
Angle Of Incidence ◽  
Axial Fan ◽  
Simple Method ◽  
Camber Angle ◽  
Fan Blade ◽  
Existing Data ◽  
Selection Of

Existing data on aerofoil sections suitable for axial flow fans are replotted on axes of angle of incidence against camber angle. The carpet plots so obtained permit the best operating conditions for each type of aerofoil to be immediately identified and thus the most suitable section can be easily selected for a given specification. A design method based on the use of these carpet plots is proposed and illustrated with a numerical example.

scholarly journals Analytical and numerical investigation of the optimum pressure distribution along a low-pressure axial fan blade

2008 ◽  
Vol 223 (3) ◽  
pp. 643-657 ◽  
Author(s):  
M Pascu ◽  
M Miclea ◽  
P Epple ◽  
A Delgado ◽  
F Durst
Keyword(s):  
Total Pressure ◽  
Design Method ◽  
Flow Characteristics ◽  
Axial Flow ◽  
Critical Parameters ◽  
Design Strategies ◽  
Axial Fan ◽  
Optimum Pressure ◽  
Absolute Increase ◽  
Fan Blade

In the field of axial flow turbomachines, the two-dimensional cascade model is often used experimentally or numerically to investigate fundamental flow characteristics and overall performance of the impeller. The core of the present work is a design method for axial fan cascades aiming to derive inversely the optimum blade shape based on the requirements of the impeller and not using any predefined aerofoil profiles. While most design strategies based on the aerofoil theory assume constant total pressure at all streamlines, i.e. free-vortex flow, this paper investigates the possibility of varying the total pressure along the blade and based on that, an analytical expression of the outlet blade angle is determined. When computing the blade profile at a specified radius, critical parameters reflecting on the flow characteristics are observed and adjusted (i.e. sufficient lift and controlled deceleration of the flow on the contour) so that the resulting profile is derived for minimum losses. The validation of this design strategy is given by the numerical results obtained when employed as an optimization tool for an industrial fan: 10–20 per cent absolute increase in the static efficiency of the optimized impeller.

scholarly journals Experimental investigations of the turbulent swirl flow in straight conical diffusers with various angles

2017 ◽  
Vol 21 (suppl. 3) ◽  
pp. 725-736 ◽  
Author(s):  
Dejan Ilic ◽  
Miroslav Benisek ◽  
Djordje Cantrak
Keyword(s):  
Flow Parameter ◽  
Flow Characteristics ◽  
Axial Flow ◽  
Swirl Flow ◽  
Experimental Investigations ◽  
Axial Fan ◽  
Flow Loss ◽  
Inlet Swirl ◽  
Loss Coefficients ◽  
Total Divergence

Results of experimental investigations of the turbulent swirl flow in three straight conical diffusers with various diffuser total angles are presented in this paper. All three diffusers have the inlet diameter 0.4 m and total divergence angles 8.6?, 10.5?, and 12.6?. The incompressible swirl flow field is generated by the axial fan impeller, and for each diffuser several regimes were achieved by changing rotation number. Original classical probes were used for measurements. The distributions of the average main swirl flow characteristics along the diffuser are shown. Distributions of the inlet Boussinesq number, outlet Coriolis coefficient, ratio of the swirl and completely axial flow loss coefficients at conical diffuser on the inlet swirl flow parameter are also presented.

Flow-separation-control system operating in feedback closed loop

2019 ◽  
Vol 91 (3) ◽  
pp. 498-508
Author(s):  
Wienczyslaw Stalewski ◽  
Andrzej Krzysiak
Keyword(s):  
Flow Separation ◽  
Closed Loop ◽  
Pressure Sensors ◽  
The Self ◽  
Experimental Investigations ◽  
Separation Control ◽  
Trailing Edge ◽  
High Lift ◽  
Content Type ◽  
Flow Separation Control

Purpose The purpose of this study is to develop the concept of self-adapting system which would be able to control a flow on the wing-high-lift system and protect the flow against strong separation. Design/methodology/approach The self-adapting system has been developed based on computational approach. The computational studies have been conducted using the URANS solver. The experimental investigations have been conducted to verify the computational results. Findings The developed solution is controlled by closed-loop-control (CLC) system. As flow actuators, the main-wing trailing-edge nozzles are proposed. Based on signals received from the pressure sensors located at the flap trailing edge, the CLC algorithm changes the amount of air blown from the nozzles. The results of computational simulations confirmed good effectiveness and reliability of the developed system. These results have been partially confirmed by experimental investigations. Research limitations/implications The presented research on an improvement of the effectiveness of high-lift systems of modern aircraft was conducted on the relatively lower level of the technology readiness. However, despite this limitation, the results of presented studies can provide a basis for developing innovative self-adaptive aerodynamic systems that potentially may be implemented in future aircrafts. Practical implications The studies on autonomous flow-separation control systems, operating in a closed feedback loop, are a great hope for significant advances in modern aeronautical engineering, also in the UAV area. The results of the presented studies can provide a basis for developing innovative self-adaptive aerodynamic systems at a higher level of technological readiness. Originality/value The presented approach is especially original and valuable in relation to the innovative concept of high-lift system supported by air-jets blown form the main-wing-trailing-edge nozzles; the effective and reliable flow sensors are the pressure sensors located at the flap trailing edge, and the effective and robust algorithm controlling the self-adapting aerodynamic system – original especially in respect to a strategy of deactivation of flow actuators.

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