Aerodynamic and Aeroacoustic Performance of a Skewed Rotor

2003 ◽  
Author(s):  
Na Cai ◽  
Jianzhong Xu ◽  
Azemi Benaissa
Keyword(s):  
Noise Reduction ◽  
Three Dimensional ◽  
Axial Flow ◽  
Pressure Rise ◽  
Broadband Noise ◽  
Rotor Blades ◽  
Skew Angle ◽  
Frequency Spectra ◽  
Stall Margin ◽  
Aerodynamic Parameters

This paper presents an experimental investigation and numerical simulation of the aerodynamic and aeroacoustic performance of an axial-flow fan with skewed rotating blades in the design and off-design operation. The blade is designed with a forward skew angle for which the stacking line is directed towards the rotating direction on the circumferential section. A detailed investigation of a three-dimensional flow field in the inter-blade row and passage using five-hole probes and a hot-wire anemometer at the upstream and downstream locations of the rotors has been carried out and compared with a fan with unskewed rotor blades. Noise testing was performed in the anechoic chamber. The experiments were performed at three rotating speeds. Aerodynamic curves show that the performance of the skewed blade increased at a higher pressure rise of 13.1% and gave a larger flow rate of about 5% and a higher efficiency of more than 3%. The higher efficiency in the skewed rotor was due to the practical and advantageous spanwise redistribution of aerodynamic parameters, a greater boundary movement into the main flow, a secondary flow reduction and the thinness of the rotor wake. Aeroacoustic performance and frequency spectra in almost the whole frequency domain showed a noise reduction of 2 to 4 dBA in the skewed fan. Lower noise in the skewed blade comes from the broadband noise reduction owing to a thinner wake layer, a phase difference in rotor radiation and tip leakage noise reduction. A wider stall margin for more than 20% is obtained in the skewed blade due to the proportional distribution of aerodynamic parameters. The three-dimensional Navier-Stokes approach is simulated in the inner blade flow.

Aerodynamics of Contra-Rotating Fans With Swept Blades

2015 ◽  
Author(s):  
K. Vijayraj ◽  
M. Govardhan
Keyword(s):  
Rotational Speed ◽  
Axial Flow ◽  
Pressure Rise ◽  
Aerodynamic Performance ◽  
The Other ◽  
Flow Structures ◽  
Current Investigation ◽  
Rotating System ◽  
Stall Margin ◽  
Static Head

A Counter-Rotating System (CRS) is composed of a front rotor and a rear rotor which rotates in the opposite direction. Compared with traditional rotor-stator system, the rear rotor is used not only to recover the static head but also to supply energy to the fluid. Therefore, to achieve the same performance, the use of a CRS may lead to a reduction of the rotational speed and may generate better homogeneous flow downstream of the stage. On the other hand, the mixing area in between the two rotors induces complicated interacting flow structures. Blade sweep has attracted the turbomachinery blade designers owing to a variety of performance benefits it offers. However, the effect of blade sweep on the performance, stall margin improvements whether it is advantageous/disadvantageous to sweep one or both rotors has not been studied till now. In the current investigation blade sweep on the performance characteristics of contra rotating axial flow fans are studied. Two sweep schemes (axial sweeping and tip chord line sweeping) are studied for two sweep angles (20° and 30°). Effect of blade sweep on front rotor and rear rotor are dealt separately by sweeping one at a time. Both rotors are swept together and effect of such sweep scheme on the aerodynamic performance of the stage is also reported here. The performance of contra rotating fan is significantly affected by all these parameters. Blade sweep improved the pressure rise and stall margin of front rotors. Axially swept rotors are found to have higher pressure rise with reduced incidence losses near the tip for front rotors. Sweeping the rear rotor is not effective since the pressure rise is less than that of unswept rotor and also has less stall margin.

Generation Mechanism of Broadband Whoosh Noise in an Automotive Turbocharger Centrifugal Compressor

2021 ◽  
pp. 1-35
Author(s):  
Rick Dehner ◽  
Pranav Sriganesh ◽  
Ahmet Selamet ◽  
Keith Miazgowicz
Keyword(s):  
Centrifugal Compressor ◽  
Combustion Engine ◽  
Three Dimensional ◽  
Leading Edge ◽  
Broadband Noise ◽  
Rotor Blades ◽  
Generation Mechanism ◽  
Primary Concern ◽  
Frequency Range ◽  
Modal Decomposition

Abstract The present study focuses on the acoustics of a turbocharger centrifugal compressor from a spark-ignition internal combustion engine. Whoosh noise is typically the primary concern for this type of compressor, which is loosely characterized by broadband sound elevation in the 4 to 13 kHz range. To identify the generation mechanism of broadband whoosh noise, the present study combines three approaches: three-dimensional (3D) computational fluid dynamics (CFD) predictions, experiments, and modal decomposition of 3D CFD results. After establishing the accuracy of predictions, flow structures and time-resolved pressures are closely examined in the vicinity of the main blade leading edge. This reveals the presence of rotating instabilities that may interact with the rotor blades to generate noise. An azimuthal modal decomposition is performed on the predicted pressure field to determine the number of cells and the frequency content of these rotating instabilities. The strength of the rotating instabilities and the frequency range in which noise is generated as a consequence of the rotor-rotating instability interaction, is found to correspond well with the qualitative trend of the whoosh noise that is measured several duct diameters upstream of the rotor blades. The variation of whoosh frequency range between low and high rotational speeds is interpreted through this analysis. It is also found that the whoosh noise primarily propagates along the duct as acoustic azimuthal modes. Hence, the inlet duct diameter, which governs the cut-off frequency for multi-dimensional acoustic modes, determines the lower frequency bound of the broadband noise.

Experimental study of wavy trailing edge serrations on flat rotor blades

2021 ◽  
Vol 263 (5) ◽  
pp. 1855-1866
Author(s):  
Sai Manikanta Kaja ◽  
K. Sriinivasan ◽  
A. Jaswanth Kalyan Kumar
Keyword(s):  
Experimental Study ◽  
Noise Reduction ◽  
Pitch Angle ◽  
Acoustic Emissions ◽  
Broadband Noise ◽  
Rotor Blades ◽  
Tonal Noise ◽  
Trailing Edge ◽  
Low Speeds ◽  
Trailing Edge Serrations

A detailed experimental study is conducted to observe the effect of various parameters like wavelength, depth of serrations, and pitch angle on serrated blades' acoustic emissions at low speeds up to 2000 rpm. Experiments are conducted on flat blade rotors with sinusoidal serrations on the trailing edge of blades with different amplitudes and wavelengths. A total of 7 blades with different serration configurations, including a base configuration, are studied, five of them have serrations throughout the span of the blade, and one configuration has serration of varying amplitude on the farther half of the blade. It is observed that some blade configurations have resulted in tonal noise reduction noise as much as 8dB, whereas some of the serration configurations reduce very little to none, there is no significant effect of T.E serrations on the broadband noise emitted by the rotor. Directivity of noise generated from the rotor, the effect of serrations on the directivity of the noise is studied.

Influence of Rain Ingestion on the Endwall Treatment in an Axial Flow Compressor

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Jichao Li ◽  
Juan Du ◽  
Mingzhen Li ◽  
Feng Lin ◽  
Hongwu Zhang ◽  
...  
Keyword(s):  
Rotor Blade ◽  
Axial Flow ◽  
Pressure Rise ◽  
Water Film ◽  
Stall Margin ◽  
Axial Flow Compressor ◽  
Water Ingestion ◽  
Blade Row ◽  
Flow Compressor ◽  
The Stability

The effects of water ingestion on the performance of an axial flow compressor are experimentally studied with and without endwall treatment. The background to the work is derived from the assessment of airworthiness for an aero-engine. The stability-enhancing effects with endwall treatments under rain ingestion are not previously known. Moreover, all the endwall treatments are designed under dry air conditions in the compressor. Water ingestion at 3% and 5% relative to the design mass flow proposed in the airworthiness standard are applied to initially investigate the effects on the performance under smooth casing (SC). Results show that the water ingestions are mainly located near the casing wall after they move through the rotor blade row. The pressure rise coefficient increases, efficiency declines, and torque increases under the proposed water ingestion. The increase of the inlet water increases the thickness of the water film downstream the rotor blade row and aggravates the adverse effects on the performances. Subsequently, three endwall treatments, namely circumferential grooves, axial slots, and hybrid slots–grooves, are tested with and without water ingestion. Compared with no water ingestion, the circumferential grooves basically have no resistance to the water ingestion. The axial slots best prevent the drop of the pressure rise coefficient induced by water ingestion, and hybrid slots–grooves are the second-best place owing to the contribution of the front axial slots. Therefore, the hybrid slots–grooves can not only extend the stall margin with less efficiency penalty compared with axial slots, but also prevent rain ingestion from worsening the compressor performance.

Successive Aeroacoustic Transfer of Leading Edge Serrations From Single Airfoil to Low-Pressure Fan Application

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Till M. Biedermann ◽  
F. Kameier ◽  
C. O. Paschereit
Keyword(s):  
Noise Reduction ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Broadband Noise ◽  
Rotating Frame ◽  
Continuous Increase ◽  
Stall Margin ◽  
Wall Pressure Fluctuations ◽  
Turbulent Inflow ◽  
Fan Blade

Abstract Leading edge serrations are identified as an effective passive treatment for reducing fan broadband noise due to high turbulent inflow conditions. This paper aims to investigate the isolated effect of serrated applications in a rotating frame, covering the aerodynamic and aeroacoustic performance. With this purpose, a serration design, previously analyzed in the rigid domain, is transferred to the rotating frame, following a successive approach in form of a continuous increase of the fan blade number. This is considered as a feasible way to isolate the serration effects and to provide information on fan blade interaction and possible masking effects. Comparing blades with straight and serrated leading edges by analyzing the spectral noise reduction and the overall level result in deep insights in the underlying noise reduction mechanisms. Furthermore, analysis of phase differences by means of the wall pressure fluctuations leads to the identification of rotating flow phenomena, nonsynchronized with the rotor speed. The results obtained indicate an efficient noise reduction by the serrations in the vicinity of the design point. By use of the presented successive approach, noise reduction phenomena observed with the full rotor could be identified to be of either aeroacoustic or aerodynamic nature. A reduced noise is observed for the full rotor case, showing a reduction of blade interaction effects. At reducing flow coefficients, an improved stall margin of the serrated rotor is identified that also affects the aeroacoustic signature.

scholarly journals On the universal trends in the noise reduction due to wavy leading edges in aerofoil–vortex interaction

2019 ◽  
Vol 871 ◽  
pp. 186-211 ◽  
Author(s):  
Jacob M. Turner ◽  
Jae Wook Kim
Keyword(s):  
Noise Reduction ◽  
High Frequency ◽  
Broadband Noise ◽  
Current Work ◽  
Source Distribution ◽  
Source Analysis ◽  
Frequency Noise ◽  
Frequency Spectra ◽  
Low Frequencies ◽  
Leading Edges

Existing studies suggest that wavy leading edges (WLEs) offer substantial reduction of broadband noise generated by an aerofoil undergoing upstream vortical disturbances. In this context, there are two universal trends in the frequency spectra of the noise reduction which have been observed and reported to date: (i) no significant reduction at low frequencies followed by (ii) a rapid growth of the noise reduction that persists in the medium-to-high frequency range. These trends are known to be insensitive to the aerofoil type and flow condition used. This paper aims to provide comprehensive understandings as to how these universal trends are formed and what the major drivers are. The current work is based on very-high-resolution numerical simulations of a semi-infinite flat-plate aerofoil impinged by a prescribed divergence-free vortex in an inviscid base flow at zero incidence angle, continued from recent work by the authors (Turner & Kim, J. Fluid Mech., vol. 811, 2017, pp. 582–611). One of the most significant findings in the current work is that the noise source distribution on the aerofoil surface becomes entirely two-dimensional (highly non-uniform in the spanwise direction as well as streamwise) at high frequencies when the WLE is involved. Also, the sources downstream of the LE make crucial contributions to creating the universal trends across all frequencies. These findings contradict the conventional LE-focused one-dimensional source analysis that has widely been accepted for all frequencies. The current study suggests that the universal trends in the noise-reduction spectra can be properly understood by taking the downstream source contributions into account, in terms of both magnitude and phase variations. After including the downstream sources, it is shown in this paper that the first universal trend is due to the conservation of total (surface integrated) source energy at low frequencies. The surface-integrated source magnitude that decreases faster with the WLE correlates very well with the noise-reduction spectrum at medium frequencies. In the meantime, the high-frequency noise reduction is driven almost entirely by destructive phase interference that increases rapidly and consistently with frequency, explaining the second universal trend.

scholarly journals Recessed Casing Treatment Effects on Fan Performance and Flow Field

1995 ◽  
Author(s):  
C. S. Kang ◽  
A. B. McKenzie ◽  
R. L. Elder
Keyword(s):  
Flow Field ◽  
Axial Flow ◽  
Pressure Rise ◽  
Operating Efficiency ◽  
Flow Measurements ◽  
Blade Loading ◽  
Stall Margin ◽  
Casing Treatment ◽  
Stall Margin Improvement ◽  
Blade Tip

An experimental investigation to examine the influence of the vaned recess casing treatment on stall margin, operating efficiency and the flow field of a low speed axial flow fan with aerospace type blade loading is presented. Different geometrical designs of the vaned passages were examined. The best configuration resulted in a stall margin improvement of 67%, a significantly higher pressure rise in the stall region and insignificant change in peak efficiency. Detailed 3-D flow measurements in the endwall region and in the casing recess were carried out with a slanted hot-wire, providing some insight to the operation of the device. The results revealed that the stall margin improvement was largely due to the removal of flow from the blade tip to the recess, and the elimination of the growth of the stall region at the tip, which occurs at stall in the solid casing build.

scholarly journals Inner Workings of Aerodynamic Sweep

1997 ◽  
Author(s):  
A. R. Wadia ◽  
P. N. Szucs ◽  
D. W. Crall
Keyword(s):  
Boundary Layer ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Axial Flow ◽  
Tip Clearance ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Stall Margin ◽  
Design Speed ◽  
The Impact

The recent trend in using aerodynamic sweep to improve the performance of transonic blading has been one of the more significant technological evolutions for compression components in turbomachinery. This paper reports on the experimental and analytical assessment of the pay-off derived from both aft and forward sweep technology with respect to aerodynamic performance and stability. The single stage experimental investigation includes two aft-swept rotors with varying degree and type of aerodynamic sweep and one swept forward rotor. On a back-to-back test basis, the results are compared with an unswept rotor with excellent performance and adequate stall margin. Although designed to satisfy identical design speed requirements as the unswept rotor, the experimental results reveal significant variations in efficiency and stall margin with the swept rotors. At design speed, all the swept rotors demonstrated a peak stage efficiency level that was equal to that of the unswept rotor. However, the forward-swept rotor achieved the highest rotor-alone peak efficiency. At the same time, the forward-swept rotor demonstrated a significant improvement in stall margin relative to the already satisfactory level achieved by the unswept rotor. Increasing the level of aft sweep adversely affected the stall margin. A three-dimensional viscous flow analysis was used to assist in the interpretation of the data. The reduced shock/boundary layer interaction, resulting from reduced axial flow diffusion and less accumulation of centrifuged blade surface boundary layer at the up, was identified as the prime contributor to the enhanced performance with forward sweep. The impact of tip clearance on the performance and stability for one of the aft-swept rotors was also assessed.

Improving Stall Margin by Using an Air-Separator for a Variable-Pitch Axial-Flow Fan

2004 ◽  
Author(s):  
Takahiro Nishioka ◽  
Shuuji Kuroda ◽  
Tadashi Kozu
Keyword(s):  
Axial Flow ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Axial Flow Fan ◽  
Clearance Ratio ◽  
Variable Pitch ◽  
Stall Margin ◽  
Operating Range ◽  
Exposure Ratio ◽  
Air Separator

An air-separator for extending the operating range of a variable-pitch axial-flow fan has been developed. It has a circular-are outer casing, a part of which forms the guide vane at the inlet of the air-separator. To obtain a wide operating range and to minimize penalties in terms of efficiency and noise, the influence of exposure and clearance ratios at various stagger-angle settings for rotor blades in low-speed and high-speed axial flow fans was experimentally investigated. Flow distributions and pressure fluctuations downstream of the rotor were also measured in order to investigate the influence of the air-separator on rotating stall. The distributions and fluctuations suggested that the air-separator decreased the blockage effect near the rotor tip and suppressed the rotating stall. Moreover, stall-margin and pressure-rise improvements were independent of the clearance ratio. These improvements depended on the exposure ratio and stagger-angle settings for the rotor blades. The fan efficiency for the air-separator also depended on the exposure ratio. In addition, the efficiency had the opposite tendency to the stall-margin and pressure-rise improvements. In contrast, the noise for the air-separator was independent of the exposure ratio and decreased as the clearance ratio increased. For the optimum combination of the exposure and clearance ratios, the stall-margin and pressure-rise were improved by over 20% with minimized penalties in terms of efficiency and noise. It is concluded from these results that the developed air-separator can provide a wide operating range for a variable-pitch axial-flow fan.

Numerical Analysis of an Industrial Fan Fitted With Noise Reduction Devices

2006 ◽  
Author(s):  
J. Amaral Teixeira ◽  
E. Naylor ◽  
P. C. Ivey ◽  
A. G. Sheard ◽  
I. R. Kinghorn
Keyword(s):  
Numerical Analysis ◽  
Noise Reduction ◽  
Flow Characteristics ◽  
Pressure Rise ◽  
Broadband Noise ◽  
Noise Sources ◽  
Fan Noise ◽  
Trailing Edge ◽  
Low Speed ◽  
The Individual

The reduction of noise emitted by industrial low speed cooling fans, particularly those fitted to air conditioning systems is a concern to fan manufacturers. The market for industrial low speed fans is highly competitive, with fan noise being the major differentiating factor between competing products. Noise reduction strategies are therefore implemented but these can adversely affect the fan’s pressure delivery capability. A reduction of fan speed can also lead to a reduction in fan noise but this is usually accompanied by a corresponding reduction in pressure rise and flow rate. The practical difficulties associated with maintaining fan pressure and flow characteristics while simultaneously reducing fan noise present fan manufacturers with a challenge. Traditional empirical approaches to the reduction of fan noise have almost been exhausted and no longer offer the potential to significantly reduce fan noise. The understanding of the aerodynamic mechanisms that act as broadband noise sources in low speed fans has been the subject of a considerable number of papers over many years. For most fans operating as a single blade row, the main sources of noise, other than those dependent on the incident turbulence levels, depend on the trailing edge and tip gap flow conditions. A range of strategies seeking to control the noise generated by these regions have been proposed over time by various authors and a number of these schemes have reached production status. The current paper details the numerical analysis of an industrial low speed fan, commonly used in conjunction with a cooling matrix, and which incorporates two distinct noise reduction features; trailing edge crenulations and a blade tip fence. Comparisons are carried out between various combinations of blades, with and without the individual features, and a discussion of the aerodynamics of the particular configurations is undertaken from a perspective of their noise reduction capabilities.

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