scholarly journals Prediction of the Aero-Acoustic Performance of Open Rotors

2014 ◽  
Author(s):  
Dale E. Van Zante ◽  
Edmane Envia
Keyword(s):  
Acoustic Field ◽  
Measurement Techniques ◽  
Three Dimensional ◽  
Primary Source ◽  
Decisive Role ◽  
Operating Conditions ◽  
Tip Vortex ◽  
Rotor Wake ◽  
Rotor Noise ◽  
Open Rotor

The rising cost of jet fuel has renewed interest in contra-rotating open rotor propulsion systems. Contemporary design methods offer the potential to maintain the inherently high aerodynamic efficiency of open rotors while greatly reducing their noise output, something that was not feasible in the 1980’s designs. The primary source mechanisms of open rotor noise generation are thought to be the front rotor wake and tip vortex interacting with the aft rotor. In this paper, advanced measurement techniques and high-fidelity prediction tools are used to gain insight into the relative importance of the contributions to the open rotor noise signature of the front rotor wake and rotor tip vortex. The measurements include three-dimensional particle image velocimetry of the intra-rotor flowfield and the acoustic field of a model-scale open rotor. The predictions provide the unsteady flowfield and the associated acoustic field. The results suggest that while the front rotor tip vortex can have a significant influence on the blade passing tone noise produced by the aft rotor, the front rotor wake plays the decisive role in the generation of the interaction noise produced as a result of the unsteady aerodynamic interaction of the two rotors. At operating conditions typical of takeoff and landing operations, the interaction noise level is easily on par with that generated by the individual rotors, and in some cases is even higher. This suggests that a comprehensive approach to reducing open rotor noise should include techniques for mitigating the wake of the front rotor as well as eliminating the interaction of the front rotor tip vortex with the aft rotor blade tip.

scholarly journals The Influence of an Upstream Pylon on Open Rotor Aerodynamics at Angle of Attack

2019 ◽  
Vol 141 (2) ◽  
Author(s):  
Nishad G. Sohoni ◽  
Cesare A. Hall ◽  
Anthony B. Parry
Keyword(s):  
Potential Field ◽  
Angle Of Attack ◽  
Separated Flow ◽  
Rotor Blades ◽  
Tip Vortex ◽  
Rotor Wake ◽  
Rotor Aerodynamics ◽  
Open Rotor ◽  
Urans Cfd ◽  
Work Done

The aerodynamic impact of installing a horizontal pylon in front of a contra-rotating open rotor engine, at take-off, was studied. The unsteady interactions of the pylon's wake and potential field with the rotor blades were predicted by full-annulus URANS CFD calculations at 0 deg and 12 deg angle of attack (AoA). Two pylon configurations were studied: one where the front rotor blades move down behind the pylon (DBP), and one where they move up behind the pylon (UBP). When operating at 12 deg AoA, the UBP orientation was shown to reduce the rear rotor tip vortex sizes and separated flow regions, whereas the front rotor wake and vortex sizes were increased. In contrast, the DBP orientation was found to reduce the incidence variations onto the front rotor, leading to smaller wakes and vortices. The engine flow was also time-averaged, and the variation in work done on average midspan streamlines was shown to depend strongly on variation in incidence, along with a smaller contribution related to change of radius.

Analysis of a LPT Rotor Blade for a Geared Engine: Part II — Characterization of the Time-Varying Flow Field in a Single Stage Research Turbine

2016 ◽  
Author(s):  
Daniele Infantino ◽  
Francesca Satta ◽  
Daniele Simoni ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
...  
Keyword(s):  
Flow Field ◽  
Rotor Blade ◽  
Large Scale ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Single Stage ◽  
Tip Vortex ◽  
Time Dependent ◽  
Exit Plane ◽  
Open Rotor

The present paper is the second part of a two-part paper focused on the design and the analysis of an optimized rotor blade for a geared open rotor engine. This part is focused on the experimental investigation of the three-dimensional unsteady flow field at the exit plane of a rotor row installed in a large scale single-stage low speed research turbine. The investigation is aimed at in depth characterizing the wake-boundary layer and the vortex-vortex interaction processes induced by the rotor-stator relative motion. Measurements have been carried out at a typical aeroengine cruise condition Reynolds number. The rotor blade aerodynamic loadings at different blade spans have been measured. A five-hole probe has been used to assess the row efficiency and detailed hot-wire phase-locked ensemble-averaged data have been analyzed to characterize the three-dimensional time-dependent flow field at the rotor exit plane. Results clearly highlight a significant distortion of the rotor blade wake and tip vortex during the migration of the high turbulence regions (wake and secondary flows) associated with the upstream stator. The unsteady interaction between the stator secondary flows and the rotor passage vortex provokes a time dependent movement of the low momentum area at the hub surface, sensibly modifying the penetration of the rotor secondary flows in an incoming stator wake passage period. The comparison of deterministic and random velocity fluctuations also allows the distinction between the structures generated by the stator and those due to the rotor.

A Contra-Rotating Open Rotor Noise Reduction Methodology by Using Anhedral Blade Tip

2021 ◽  
pp. 1-26
Author(s):  
Tianxiao Yang ◽  
Wenjun Yu ◽  
Dong Liang ◽  
Xiang He ◽  
Zhenguo Zhao
Keyword(s):  
Noise Reduction ◽  
Polar Angle ◽  
Aerodynamic Performance ◽  
Tip Vortex ◽  
Rotor Noise ◽  
Lean Angle ◽  
Open Rotor ◽  
Blade Tip

Abstract In this paper, a novel Contra-Rotating Open Rotor (CROR) noise reduction methodology based upon the anhedral blade tip applied to the front blade is developed. Results indicate that anhedral blade tip can provide noise reduction over 60 deg. polar angle range in both upstream and downstream areas at takeoff condition. The noise reduction becomes more significant as the lean angle of anhedral blade tip increases, and the maximum noise reduction is over 4 dB. Further analysis shows that anhedral blade tip decreases the strength and size of blade tip vortex shed from the front blade, and reduces its interaction with the rear rotor, which decreases the fluctuation of loading acting on the rear rotor and its loading noise. Furthermore, the anhedral blade tip does not have strong effect on the aerodynamic performance of CROR at cruise.

Contrarotating Open Rotor Operation for Improved Aerodynamics and Noise at Takeoff

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Alexios Zachariadis ◽  
Cesare Hall ◽  
Anthony B. Parry
Keyword(s):  
Rotational Speed ◽  
Carbon Dioxide Emissions ◽  
Three Dimensional ◽  
Separated Flow ◽  
Operating Conditions ◽  
Aviation Fuel ◽  
Lower Velocity ◽  
Speed Increase ◽  
Community Noise ◽  
Open Rotor

The contrarotating open rotor is, once again, being considered as an alternative to the advanced turbofan to address the growing pressure to cut aviation fuel consumption and carbon dioxide emissions. One of the key challenges is meeting community noise targets at takeoff. Previous open rotor designs are subject to poor efficiency at takeoff due to the presence of large regions of separated flow on the blades as a result of the high incidence needed to achieve the required thrust. This is a consequence of the fixed rotor rotational speed constraint typical of variable pitch propellers. Within the study described in this paper, an improved operation is proposed to improve performance and reduce rotor-rotor interaction noise at takeoff. Three-dimensional computational fluid dynamics (CFD) calculations have been performed on an open rotor rig at a range of takeoff operating conditions. These have been complemented by analytical tone noise predictions to quantify the noise benefits of the approach. The results presented show that for a given thrust, a combination of reduced rotor pitch and increased rotor rotational speed can be used to reduce the incidence onto the front rotor blades. This is shown to eliminate regions of flow separation, reduce the front rotor tip loss and reduce the downstream stream tube contraction. The wakes from the front rotor are also made wider with lower velocity defect, which is found to lead to reduced interaction tone noise. Unfortunately, the necessary increase in blade speed leads to higher relative Mach numbers, which can increase rotor alone noise. In summary, the combined CFD and aeroacoustic analysis in this paper shows how careful operation of an open rotor at takeoff, with moderate levels of repitch and speed increase, can lead to improved front rotor efficiency as well as appreciably lower overall noise across all directivities.

Three-Dimensional Unsteady Flow Field due to Rotor-Stator Interaction in the Tip Region of an Axial Compressor Stator Passage

2001 ◽  
Author(s):  
Hongwei Ma ◽  
Haokang Jiang ◽  
Qingguo Zhang
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Measurement Techniques ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Low Energy ◽  
Separation Flow ◽  
Rotor Wake ◽  
Flow Mixing ◽  
Rotor Stator Interaction

This paper reports an experimental study of the three-dimensional unsteady flow field due to rotor-stator interaction in the tip region of an axial compressor stator passage. The measurements were conducted on a low-speed large-scale axial compressor using a 3-component Laser Doppler Velocimetry. Both experimental method and measurement techniques are presented in details. The measurement results indicate that the rotor tip leakage vortex and the rotor wake periodically pass through the tip region of a stator passage, resulting in periodical flow blockages and fluctuations in the stator passage. In the meantime, the wake is catching up with the last rotor leakage vortex. The interaction and the flow mixing between the vortex and the wake occur in a stator passage, leading to more substantial fluctuations in the flow field. The rotor lip leakage vortex has a stronger influence on the downstream endwall flow than the rotor wake. The low-energy fluids from the upstream tend to accumulate toward the pressure surface of a stator blade. The separation flow near the suction surface is found in the rear of a stator passage. The interaction and the flow mixing are observed among the low-energy fluids from the upstream and the separation flow.

Cavitation in the Tip Region of the Rotor Blades Within a Waterjet Pump

2008 ◽  
Author(s):  
H. Wu ◽  
F. Soranna ◽  
T. Michael ◽  
J. Katz ◽  
S. Jessup
Keyword(s):  
Measurement Techniques ◽  
Leading Edge ◽  
Suction Side ◽  
Operating Conditions ◽  
Index Of Refraction ◽  
Rotor Blades ◽  
Tip Vortex ◽  
Working Fluid ◽  
Pressure Side ◽  
Cavitation Inception

Recent upgrades to the turbomachinery facility at JHU enable measurements of performance, as well as flow structure, turbulence and cavitation within a water-jet pump. The rotor, stator and pump casing in this optically index-matched facility are made of acrylic that has the same optical index of refraction as the working fluid, a concentrated solution of NaI in water. The essentially “invisible” blades allow unobstructed view and access to optical flow measurement techniques. Initial tests in water focus on observations on occurrence of cavitation in the vicinity of the narrow tip-gap. For the present design and operating conditions, near the leading edge, cavitation in the tip corner of the pressure side causes accumulation of bubbles along the pressure side that extends to mid blade. As rollup of a tip vortex starts, these bubbles cross the tip gap to the suction side, and become primary nuclei for cavitation inception within the tip leakage vortex (TLV). Bursting of this tip vortex as it migrates towards the pressure side of the neighboring blade generates a cloud of bubbles along the aft section of the passage. As the flow in the tip gap increases upstream of the trailing edge, cavitation also develops within the gap, along the pressure side corner.

Contra-Rotating Open Rotor Operation for Improved Aerodynamics and Noise at Takeoff

2011 ◽  
Author(s):  
Alexios Zachariadis ◽  
Cesare A. Hall ◽  
Anthony B. Parry
Keyword(s):  
Rotational Speed ◽  
Carbon Dioxide Emissions ◽  
Acoustic Analysis ◽  
Three Dimensional ◽  
Separated Flow ◽  
Operating Conditions ◽  
Aviation Fuel ◽  
Lower Velocity ◽  
Speed Increase ◽  
Open Rotor

The contra-rotating open rotor is, once again, being considered as an alternative to the advanced turbofan to address the growing pressure to cut aviation fuel consumption and carbon dioxide emissions. One of the key challenges is meeting community noise targets at takeoff. Previous open rotor designs are subject to poor efficiency at takeoff due to the presence of large regions of separated flow on the blades as a result of the high incidence needed to achieve the required thrust. This is a consequence of the fixed rotor rotational speed constraint typical of variable pitch propellers. Within the study described in this paper, an improved operation is proposed to improve performance and reduce rotor-rotor interaction noise at takeoff. Three-dimensional computational fluid dynamics (CFD) calculations have been performed on an open rotor rig at a range of takeoff operating conditions. These have been complemented by analytical tone noise predictions to quantify the noise benefits of the approach. The results presented show that for a given thrust, a combination of reduced rotor pitch and increased rotor rotational speed can be used to reduce the incidence onto the front rotor blades. This is shown to eliminate regions of flow separation, reduce the front rotor tip loss and reduce the downstream stream tube contraction. The wakes from the front rotor are also made wider with lower velocity defect, which is found to lead to reduced interaction tone noise. Unfortunately, the necessary increase in blade speed leads to higher relative Mach numbers, which can increase rotor alone noise. In summary, the combined CFD and aero-acoustic analysis in this paper shows how careful operation of an open rotor at takeoff, with moderate levels of re-pitch and speed increase, can lead to improved front rotor efficiency as well as appreciably lower overall noise across all directivities.

Numerical Investigation of the Aerodynamic Performance of Hybrid Aerofoils in a 1.5-Stage Low-Speed Compressor

2021 ◽  
Author(s):  
Jannik Eckel ◽  
Volker Gümmer
Keyword(s):  
Secondary Flow ◽  
Numerical Investigation ◽  
Three Dimensional ◽  
Aerodynamic Performance ◽  
Operating Conditions ◽  
Tip Vortex ◽  
Limiting Factors ◽  
Stall Inception ◽  
Low Speed ◽  
Flow Phenomena

Abstract This paper describes the numerical investigation of hybrid aerofoils in a 1.5-stage low-speed compressor, which in its baseline configuration features a conventional rotor and a tandem stator. Both of these are eventually replaced by hybrid aerofoils, using the initial tandem blade profile geometry around mid-span. In this course of design investigations a pure tandem rotor was also generated and analysed as the initial geometry of the hybrid rotor. The aerodynamic design and performance of the tandem rotor and the hybrid aerofoils will be discussed in this paper. The numerical analysis is aimed at understanding the secondary flow phenomena and limiting factors of the working range of the reference stage. Based on this knowledge, the advantages of the hybrid aerofoil design will be discussed. On one hand, the origin and development of three-dimensional flow structures near the endwall regions of the rear vane of the tandem stator are investigated in detail, as they appear to play a major role at de-throttled operating conditions. On the other hand, the tip vortex leakage of the single rotor and the pure tandem rotor are considered, showing the tip vortex taking a major role in loss generation and stall inception at throttled operating conditions, and interacting with the tandem stator secondary flow phenomena at the casing. Both these performance-limiting factors can be addressed by implementing hybrid aerofoils. The paper presents and discusses the improvement of secondary flow loses and aerodynamic performance based on steady-state RANS simulations.

Application of a Navier-Stokes Solver to the Study of Open Rotor Aerodynamics

2009 ◽  
Author(s):  
Alexios Zachariadis ◽  
Cesare A. Hall
Keyword(s):  
Control Volume ◽  
Three Dimensional ◽  
Computational Approach ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Computational Results ◽  
Field Boundary ◽  
Rotor Aerodynamics ◽  
Open Rotor ◽  
Good Agreement

This paper establishes a proven computational approach for open rotor configurations that can be used as a basis for further studies involving open rotor aerodynamics and design. Many of the difficulties encountered in the application of computational fluid dynamics to an open rotor engine arise due to the removal of the casing that is present in conventional aeroengine turbomachinery. In this work, an advanced three-dimensional Navier-Stokes solver is applied to the open rotor. The approach needed to accurately capture the aerodynamics is investigated with particular attention to the mesh configuration and the specification of boundary conditions. A new three-step meshing strategy for generating the mesh and the most suitable type of far-field boundary condition are discussed. A control volume analysis approach is proposed for post-processing the numerical results for rotor performance. The capabilities of the solver and the applied methodology are demonstrated at both cruise and take-off operating conditions. The comparison of computational results with experimental measurements shows good agreement for both data trend and magnitudes.

Application of a Navier–Stokes Solver to the Study of Open Rotor Aerodynamics

2010 ◽  
Vol 133 (3) ◽  
Author(s):  
Alexios Zachariadis ◽  
Cesare A. Hall
Keyword(s):  
Control Volume ◽  
Three Dimensional ◽  
Computational Approach ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Field Boundary ◽  
Rotor Aerodynamics ◽  
Aero Engine ◽  
Open Rotor ◽  
Good Agreement

This paper establishes a proven computational approach for open rotor configurations that can be used as a basis for further studies involving open rotor aerodynamics and design. Many of the difficulties encountered in the application of computational fluid dynamics to an open rotor engine arise due to the removal of the casing that is present in conventional aero-engine turbomachinery. In this work, an advanced three-dimensional Navier–Stokes solver is applied to the open rotor. The approach needed to accurately capture the aerodynamics is investigated with particular attention to the mesh configuration and the specification of the boundary conditions. A new three-step meshing strategy for generating the mesh and the most suitable type of far-field boundary condition are discussed. A control volume analysis approach is proposed for post-processing the numerical results for the rotor performance. The capabilities of the solver and the applied methodology are demonstrated at both cruise and take-off operating conditions. The comparison of the computational results with the experimental measurements shows good agreement for both data trend and magnitudes.

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