scholarly journals Experimental Study of the Instationary Flow Between Two Ducted Counter-Rotating Rotors

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
H. Nouri ◽  
A. Danlos ◽  
F. Ravelet ◽  
F. Bakir ◽  
C. Sarraf
Keyword(s):  
Design Method ◽  
Radial Profile ◽  
Tangential Velocity ◽  
Pressure Rise ◽  
Axial Distance ◽  
Flow Angle ◽  
Rotation Rates ◽  
Wall Pressure Fluctuations ◽  
Wide Range ◽  
High Efficient

The purpose of this work is to study experimentally the aerodynamic characteristics of a subsonic counter-rotating axial-flow fans system operating in a ducted configuration. The fans of diameter D=375 mm were designed to match the specification point using an original iterative method: the front rotor blade cascade is designed with a conventional inverse method, setting the radial distribution of the Euler work. The through-flow is then computed using an axisymmetric and radial equilibrium assumption, with empirical models of losses. The rear rotor is not conventional but is designed to straighten the radial profile of the tangential velocity. The design of the front rotor is then modified until the stage meets the requirements. The experimental setup is arranged such that the rotation rate of each fan is independently controlled and that the axial distance between the rotors can be varied from 17% to 310% of the midspan chord length. Systematic measurements of the global performances and local measurements of the velocity field and of the wall pressure fluctuations are performed, in order to first validate the design method, and to explore the effects of the two specific free parameters of the system, the axial spacing and the ratio of rotation rates. The results show that the efficiency is strongly increased compared to a conventional rotor or to a rotor-stator stage. The developed design method slightly overpredicts the pressure rise and slightly underpredicts the best ratio of rotation rates. Flow angle measurements downstream of the stage show that the outflow is not completely straightened at the design point. Finally, the system is highly efficient on a wide range of flow rates and pressure rises: this system has thus a very flexible use, with a large patch of high efficient operating points in the parameter space.

scholarly journals Experimental Investigation on Ducted Counter-Rotating Axial Flow Fans

2011 ◽  
Author(s):  
Hussain Nouri ◽  
Florent Ravelet ◽  
Farid Bakir ◽  
Christophe Sarraf
Keyword(s):  
Inverse Method ◽  
Pressure Fluctuations ◽  
Axial Flow ◽  
Axial Distance ◽  
Large Patch ◽  
Rotation Rates ◽  
Wall Pressure Fluctuations ◽  
Wide Range ◽  
High Efficient ◽  
Operating Points

An experimental study on counter-rotating axial-flow fans was carried out. The fans of diameter D = 375 mm were designed using an inverse method. The counter-rotating fans operate in a ducted-flow configuration and the overall performances are measured in a normalized test bench. The rotation rate of each fan is independently controlled. The axial spacing between the fans can vary from 10 to 50 mm by steps of 10 mm. The results show that the efficiency is strongly increased compared to a conventional rotor or to a rotor-stator stage. The effects of varying the rotation rates ratio on the overall performances are studied and show that the system is highly efficient on a wide range of flow-rates and pressure rises. However, the change of the axial distance between rotors from 10 to 50 mm does not seem to change the overall performances. This system has thus a very flexible use, with a large patch of high efficient operating points in the parameter space. Further local studies including velocity measurements and wall-pressure fluctuations in the space between the rotors are needed to better understand the interactions between the rotors and to optimize the system.

Development of a New Design Method for High Efficiency Swept Low Pressure Axial Fans With Small Hub/Tip Ratio

2014 ◽  
Author(s):  
Thore Bastian Lindemann ◽  
Jens Friedrichs ◽  
Udo Stark
Keyword(s):  
High Efficiency ◽  
Design Method ◽  
Tangential Velocity ◽  
Pressure Rise ◽  
Low Pressure ◽  
Aerodynamic Performance ◽  
Low Noise ◽  
Angle Distribution ◽  
Sweep Angle ◽  
Reduced Pressure

For a competitive low pressure axial fan design low noise emission is as important as high efficiency. In this paper a new design method for low pressure fans with a small hub to tip ratio including blade sweep is introduced and discussed based on experimental investigations. Basis is an empirical axial and tangential velocity distribution at the rotor outlet combined with a distinctive sweep angle distribution along the stacking line. Several fans were designed, built and tested in order to analyze the aerodynamic as well as the aeroacoustic behavior. For the aerodynamic performance particular attention was paid to compensate the influence of reduced pressure rise and efficiency due to increasing blade sweep. This was achieved by a method of increasing the blade chord depending on the local sweep angle which is based on single airfoil data. The tested fans without this compensation revealed a significant noise reduction effect of up to approx. 6 dB(A) for a tip sweep angle of 64° which was accompanied by an unsatisfactory effect of reduced overall aerodynamic performance. The second group of fans did not only confirm the method of the aerodynamic compensation by a nearly unchanged pressure rise and efficiency characteristic but also revealed an increased aeroacoustic benefit of in average 9.5 dB(A) compared to the unswept version. Beside the overall characteristics the individual differences between the designs are also discussed using results of wall pressure measurements which show some significant changes of the blade tip flow structure.

Redesigning Annular Turbine Blade Rows Using a Viscous-Inviscid Inverse Design Method

2008 ◽  
Author(s):  
J. C. Pa´scoa ◽  
A. C. Mendes ◽  
L. M. C. Gato
Keyword(s):  
Turbine Blade ◽  
Design Method ◽  
Thickness Distribution ◽  
Tangential Velocity ◽  
Inverse Design ◽  
Angle Distribution ◽  
Flow Angle ◽  
Design Algorithm ◽  
Blade Thickness ◽  
Inverse Design Method

This paper presents the results of the aerodynamic redesign of an annular turbine blade row. The inverse method herein applied is an extension to 3D of an iterative inverse design method based on the imposition of the blade load, thickness distribution and stacking line. We define a mass-averaged mean tangential velocity over one blade pitch, ru¯θ, as the main design variable, since its derivative is related to the aerodynamic load. A time-lagged formulation for the 3D camber surface generator is given in order to include the blade thickness distribution into the design algorithm. The hybrid viscous-inviscid design code comprises three main components: the blade update algorithm; a fast inviscid 3D Euler code; and a viscous analysis code. The blade geometry and flow conditions are typical of LP turbine nozzle guide vanes. The design method will demonstrate its ability to redesign blade rows that achieve lower flow losses and a more uniform exit flow angle distribution. The performance of the new blades is checked by means of a Navier-Stokes computation using the κ–ε turbulence model. The presented results show a minor decrease in the losses and a better redistribution of the exit flow angle.

Design and Flow Analysis of a Rim-Driven Hub-Less Axial Flow Fan

2021 ◽  
Author(s):  
Hanqing Yang ◽  
Yijun Wang ◽  
Jinju Sun ◽  
Bangyi Wang ◽  
Youwei He ◽  
...  
Keyword(s):  
Design Method ◽  
Flow Behavior ◽  
Tangential Velocity ◽  
Axial Flow ◽  
Pressure Rise ◽  
Low Noise ◽  
Flow Mechanism ◽  
Axial Flow Fan ◽  
Flow Area ◽  
Overall Performance

Abstract Rim-driven hub-less fans have newly emerged as the most compact type of axial flow fans, which permits flexible configuration arrangements, large relative flow area and low-noise level operation. However, previous publications on rim-driven axial flow fans are rarely found in the open literature, and the flow mechanism and design principle of such promising fans haven’t yet been well-understood and established. This paper has been focused on a preliminary study of the rim-driven axial flow fan design and flow mechanism. A design method of the rim-driven fans is proposed on the basis of the isolated airfoil scheme and the variable circulation rule. It is further incorporated into a FORTRAN code and suited for designing the rim-driven hub-less fans of low-pressure levels. For validation purpose, a conventional hub-type fan is redesigned with the developed method and its flow behavior and overall performance are investigated numerically. A parametric study on the designed fan is further conducted respectively for the tangential velocity difference at mean span, circulation exponent and sweep angle and their influence on the fan flow characteristics and overall performance are explored and highlighted. On such a basis, the developed design method for the rim-driven axial flow fan is further improved. In comparison with the conventionally designed fan at identical rotating speed, significant comprehensive gains are arising from the redesigned fan of hub-less configuration: the overall pressure rise and static pressure efficiency is enhanced respectively by 6.2% and 11.5%, whereas the diameter of the fan is reduced by 12.5% simultaneously. It is demonstrated that the rim-driven hub-less configuration is promising for the enhancing the fan overall performance with even reduced dimensions.

A Parametric Wind–Pressure Relationship for Rankine versus Non-Rankine Cyclostrophic Vortices

2013 ◽  
Vol 30 (12) ◽  
pp. 2850-2867 ◽  
Author(s):  
Vincent T. Wood ◽  
Luther W. White
Keyword(s):  
Wind Profile ◽  
Radial Profile ◽  
Tangential Velocity ◽  
Pressure Rise ◽  
Parametric Model ◽  
Wind Pressure ◽  
Central Pressure ◽  
Shape Parameters ◽  
Rankine Vortex ◽  
Tangential Wind

Abstract A parametric tangential wind profile model is presented for depicting representative pressure deficit profiles corresponding to varying tangential wind profiles of a cyclostrophic, axisymmetric vortex. The model employs five key parameters per wind profile: tangential velocity maximum, radius of the maximum, and three shape parameters that control different portions of the profile. The model coupled with the cyclostrophic balance assumption offers a diagnostic tool for estimating and examining a radial profile of pressure deficit deduced from a theoretical superimposing tangential wind profile in the vortex. Analytical results show that the shape parameters for a given tangential wind maximum of a non-Rankine vortex have an important modulating influence on the behavior of realistic tangential wind and corresponding pressure deficit profiles. The first parameter designed for changing the wind profile from sharply to broadly peaked produces the corresponding central pressure fall. An increase in the second (third) parameter yields the pressure rise by lowering the inner (outer) wind profile inside (outside) the radius of the maximum. Compared to the Rankine vortex, the parametrically constructed non-Rankine vortices have a larger central pressure deficit. It is suggested that the parametric model of non-Rankine vortex tangential winds has good potential for diagnosing the pressure features arising in dust devils, waterspouts, tornadoes, tornado cyclones, and mesocyclones. Finally, presented are two examples in which the parametric model is fitted to a tangential velocity profile, one derived from an idealized numerical simulation and the other derived from high-resolution Doppler radar data collected in a real tornado.

Aerodynamic Design and Analysis of a Two-Stage High-Load Low-Reaction Transonic Aspirated Counter-Rotating Compressor

2017 ◽  
Author(s):  
Shijun Sun ◽  
Songtao Wang ◽  
Shaowen Chen
Keyword(s):  
High Efficiency ◽  
Design Method ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Pressure Rise ◽  
Axial Direction ◽  
High Load ◽  
Design Parameters ◽  
Two Stage ◽  
Flow Angle

The design and numerical analysis of a two-stage, highly-loaded aspirated counter-rotating compressor is presented in the current paper. Compared with the conventional counter-rotating compressor (CRC), the CRC designed in this study included the stator downstream of each rotor. The stator in the counter-rotating compressor was used for enabling static pressure rise and turning the flow towards the axial direction which would decrease inlet relative velocity and inlet flow angle respectively in the following stage. With the low-reaction design concept in combination with boundary layer suction, the two-stage counter-rotating compressor produced a total pressure ratio of 5.99 at an adiabatic efficiency of 88.15%(η1), 85.35%(η2) by aspiration only implemented on the stators. The primary intent of this unconventional design was to mitigate the complexity of the bleed system design, eliminate the adverse effects of aspiration on the blade strength in the rotating parts and finally improve the structural stability of the compressor under the premise of achieving a high-load design. The tip speed of the two rotors was 370m/s and 377.5m/s, respectively at the design rotational speeds. The design aspiration requirement for the configuration reached 22.25% of the inlet mass flow. Detail design parameters, flow characteristics and aerodynamic performance were presented and discussed. The results show that the low-reaction design methodology based on an increase in rotor exit axial velocity was feasible and the integration between low-reaction design method, aspiration and counter-rotating technology could substantially improve the stage loading coefficient meanwhile a high efficiency could be achieved.

scholarly journals The Effect of Load Control on the Performance of Contra-Rotating Fans

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1227
Author(s):  
Xi Zhang ◽  
Xingyu Jia ◽  
Xuan Jiang
Keyword(s):  
Load Distribution ◽  
Design Method ◽  
Pressure Rise ◽  
Axial Distance ◽  
Element Analysis ◽  
Load Matching ◽  
Key Factor ◽  
Flow Mechanisms ◽  
Flow Field Characteristics ◽  
The Relationship

In recent years, few studies focused on adjusting the load distribution of contra-rotating fan (CRF) blades. To improve the overall performance of CRFs, we used a design code to build 32 sets of CRFs to determine the effects of three factors—the front and rear rotor load matching, the load distribution of each rotor and the axial distance between the rotors—on the total pressure rise and efficiency of CRFs using numerical calculations. The relationship between the CRF blades load and velocity components was theoretically analyzed using blade element analysis and the forward problem method. According to the performance curve, it can be concluded that the rear rotor (RR) is the key factor that determines the performance of CRFs. Through analyzing Mach number contours from different perspectives, the relationship between velocity and adjustment load was verified. Furthermore, the flow field characteristics for three specific CRFs were explored at the stall points, design points and choke points to reveal their flow mechanisms. This study provides a reference for the CRF blade design method.

scholarly journals Nano-imprinted subwavelength gratings as polarizing beamsplitters

2021 ◽  
Vol 17 (1) ◽  
Author(s):  
Julian Wüster ◽  
Yannick Bourgin ◽  
Patrick Feßer ◽  
Arne Behrens ◽  
Stefan Sinzinger
Keyword(s):  
Nanoimprint Lithography ◽  
Optical Measurement ◽  
Design Method ◽  
Optical Systems ◽  
Surface Metrology ◽  
Measurement Systems ◽  
Common Path ◽  
Dielectric Coatings ◽  
Subwavelength Gratings ◽  
Wide Range

AbstractPolarizing beamsplitters have numerous applications in optical systems, such as systems for freeform surface metrology. They are classically manufactured from birefringent materials or with stacks of dielectric coatings. We present a binary subwavelength-structured form-birefringent diffraction grating, which acts as a polarizing beamsplitter for a wide range of incidence angles −30∘…+30∘. We refine the general design method for such hybrid gratings. We furthermore demonstrate the manufacturing steps with Soft-UV-Nanoimprint-Lithography, as well as the experimental verification, that the structure reliably acts as a polarizing beamsplitter. The experimental results show a contrast in efficiency for TE- and TM-polarization of up to 1:18 in the first order, and 34:1 in the zeroth order. The grating potentially enables us to realize integrated compact optical measurement systems, such as common-path interferometers.

Studies on Downstream Stator With Rotor Re-Staggering and Forward Sweeping in a Subsonic Axial Compressor Stage

2011 ◽  
Author(s):  
P. V. Ramakrishna ◽  
M. Govardhan
Keyword(s):  
Flow Field ◽  
Computational Model ◽  
Flow Rate ◽  
Total Pressure ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Axial Distance ◽  
Compressor Stage ◽  
Numerical Work ◽  
Stagger Angle

The present numerical work studies the flow field in subsonic axial compressor stator passages for: (a) preceding rotor sweep (b) preceding rotor re-staggering (three stagger angle changes: 0°, +3° and +5°); and (c) stator sweeping (two 20° forward sweep schemes). The following are the motives for the study: at the off-design conditions, compressor rotors are re-staggered to alleviate the stage mismatching by adjusting the rows to the operating flow incidence. Fundamental to this is the understanding of the effects of rotor re-staggering on the downstream component. Secondly, sweeping the rotor stages alters the axial distance between the successive rotor-stator stages and necessitates that the stator vanes must also be swept. To the best of the author’s knowledge, stator sweeping to suit such scenarios has not been reported. The computational model for the study utilizes well resolved hexahedral grids. A commercial CFD package ANSYS® CFX 11.0 was used with standard k-ω turbulence model for the simulations. CFD results were well validated with experiments. The following observations were made: (1) When the rotor passage is closed by re-staggering, with the same mass flow rate and the same stator passage area, stators were subjected to negative incidences. (2) Effect of stator sweeping on the upstream rotor flow field is insignificant. Comparison of total pressure rise carried by the downstream stators suggests that an appropriate redesign of stator is essential to match with the swept rotors. (3) While sweeping the stator is not recommended, axial sweeping is preferable over true sweeping when it is necessary.

Surge in a Low-Speed Radial Compressor

1998 ◽  
Author(s):  
Corine Meuleman ◽  
Frank Willems ◽  
Rick de Lange ◽  
Bram de Jager
Keyword(s):  
Flow Rate ◽  
Pressure Rise ◽  
Flow Coefficient ◽  
Lumped Parameter Model ◽  
Pressure Oscillations ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Radial Compressor ◽  
Low Speed ◽  
Lumped Parameter

Surge is measured in a low-speed radial compressor with a vaned diffuser. For this system, the flow coefficient at surge is determined. This coefficient is a measure for the inducer inlet flow angle and is found to increase with increasing rotational speed. Moreover, the frequency and amplitude of the pressure oscillations during fully-developed surge are compared with results obtained with the Greitzer lumped parameter model. The measured surge frequency increases when the compressor mass flow is throttled to a smaller flow rate. Simulations show that the Greitzer model describes this relation reasonably well except for low rotational speeds. The predicted amplitude of the pressure rise oscillations is approximately two times too small when deep surge is met in the simulations. For classic surge, the agreement is worse. The amplitude is found to depend strongly on the shape of the compressor and throttle characteristic, which are not accurately known.

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