Effect of Blade Tip Modifications for Unducted Propulsors on Tip Vortex-Rotor Interaction Noise

2014 ◽  
Author(s):  
Florian Danner ◽  
Christofer Kendall-Torry
Keyword(s):  
Rotor Blade ◽  
Stokes Equations ◽  
Acoustic Emissions ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Tip Vortices ◽  
Blade Tip ◽  
Blade Loads ◽  
Blade Tips

Front rotor tip vortices impinging on a downstream blade row of an unducted propulsor induce distinct unsteadiness to blade loads with associated sound emissions. Since the region of unsteadiness is concentrated near the blade tips, reducing the rear rotor tip diameter represents a potential means for minimising interaction noise. A survey on the aeroacoustic effects resulting from a cropped rear rotor in combination with a front rotor blade tip modification is therefore presented. Analyses are based on data from computational fluid dynamics solutions with the Reynolds-averaged Navier-Stokes equations and direct acoustic predictions. The evaluation of polar directivities, blade surface pressure disturbances and details of the unsteady flow field provide insight into the underlying phenomena. Results show that an arbitrary reduction of the rear rotor tip diameter does not necessarily decrease noise radiation and that winglet-like structures applied to the front rotor blade tips are capable of reducing acoustic emissions due to tip vortex-rotor interactions.

scholarly journals Analysis of Gas Turbine Rotor Blade Tip and Shroud Heat Transfer

1996 ◽  
Author(s):  
A. A. Ameri ◽  
E. Steinthorsson
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Rotor Blade ◽  
Stokes Equations ◽  
Computer Code ◽  
Turbine Rotor ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Turbine Rotor Blade ◽  
Blade Tip

Predictions of the rate of heat transfer to the tip and shroud of a gas turbine rotor blade are presented. The simulations are performed with a multiblock computer code which solves the Reynolds Averaged Navier-Stokes equations. The effect of inlet boundary layer thickness as well as rotation rate on the tip and shroud heat transfer is examined. The predictions of the blade tip and shroud heat transfer are in reasonable agreement with the experimental measurements. Areas of large heat transfer rates are identified and physical reasoning for the phenomena presented.

scholarly journals Aerodynamic and acoustic analysis of helicopter main rotor blade tips in hover

2016 ◽  
Vol 26 (7) ◽  
pp. 2101-2118 ◽  
Author(s):  
Lyaysan Ildusovna Garipova ◽  
Andrei Sergeevich Batrakov ◽  
Alexander Nikolaevich Kusyumov ◽  
Sergey Anatolievich Mikhaylov ◽  
George Barakos
Keyword(s):  
Rotor Blade ◽  
Acoustic Analysis ◽  
Main Rotor ◽  
Content Type ◽  
Helicopter Blades ◽  
Blade Tip ◽  
Helicopter Main Rotor ◽  
Main Rotor Blade ◽  
Blade Loads ◽  
Blade Tips

Purpose The design of main rotor blade tips is of interest to helicopter manufactures since the tip details affect the performance and acoustics of the rotor. The paper aims to discuss this issue. Design/methodology/approach In this paper, computation fluid dynamics is used to simulate the flow around hovering helicopter blades with different tip designs. For each type of blade tip a parametric study on the shape is also conducted for comparison calculations were performed the constant rotor thrust condition. The collective pitch and the cone angles of the blades were determined by at an iterative trimming process. Findings Analysis of the distributed blade loads shows that the tip geometry has a significant influence on aerodynamics and aeroacoustics especially for stations where blade loading is high. Originality/value The aeroacoustic characteristics of the rotors were obtained using Ffowcs Williams-Hawkings equations.

Open Counter-Rotation Fan Blades Optimization Based on 3D Inverse Problem Navier-Stokes Solution Method With the Aim of Tonal Noise Reduction

2008 ◽  
Author(s):  
Victor I. Mileshin ◽  
Michael A. Nyukhtikov ◽  
Igor K. Orekhov ◽  
Sergey V. Pankov ◽  
Sergey K. Shchipin
Keyword(s):  
Inverse Problem ◽  
Stokes Equations ◽  
Aerodynamic Characteristics ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Far Field ◽  
Tonal Noise ◽  
Noise Sources ◽  
Navier Stokes Equations ◽  
Counter Rotation

When developing counter-rotating fans for advanced new-generation aeroengines with unducted blades it is very important to provide high acoustic and aerodynamic characteristics [1]. This paper presents some results of gasdynamic and aeroacoustic optimization of unducted CRF blade profile by using 3D viscous inverse problem. Flow in unducted CRF on the basis of unsteady 3D Navier-Stokes equations is modeled at the 1st stage of designing in order to find the key tonal noise sources. Based on these results, it is found that one of the key tonal noise sources is Rotor 1 - Rotor 2 tip vortices interaction and potential rotor interaction. Then, using 3D solver of the viscous inverse problem, aerodynamic loads are redistributed along R1 and R2 blade height aiming at a decrease in tip vortex intensity and potential rotor interaction with a probable increase in the CRF thrust. To verify the aerodynamic characteristics of the modified CRF, steady flow calculations are carried out with the help of 3D Navier-Stokes equations and “mixing plane” interfaces. To verify the acoustic characteristics of the modified CRF, tonal noise modeling is carried out for original and modified CRFs using aeroacoustic CIAM’s 3DAS solver for solution of unsteady inviscid equations for disturbances. Ffowcs–Williams, Howkings approach is used for acoustic calculations in the far field. The near acoustic field and directivity diagrams in the far field are found. Using 3D inverse problem, the fan tonal noise is decreased by 4 dB for take-0ff and landing with no thrust and efficiency losses.

Application of a Viscous Flow Methodology to the NREL Phase VI Rotor

2002 ◽  
Author(s):  
Guanpeng Xu ◽  
Lakshmi N. Sankar
Keyword(s):  
Stokes Equations ◽  
Numerical Technique ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Local Flow ◽  
Navier Stokes Equations ◽  
Horizontal Axis Wind Turbines ◽  
Blade Tip ◽  
Bladed Rotor ◽  
Stall Angle

A numerical technique has been developed for efficiently simulating fully three-dimensional viscous fluid flow around horizontal axis wind turbines (HAWT). In this approach, the viscous region surrounding the blades is modeled using 3-D unsteady Navier-Stokes equations. The inviscid region away from the boundary layer and the wake is modeled using potential flow. The concentrated vortices that emanate from the blade tip are treated as piecewise straight line segments that are allowed to deform and convect at the local flow velocity. Biot-Savart law is used to estimate the velocity field associated with these vortices. Calculations are presented under axial wind conditions for a NREL two-bladed rotor, known as the Phase VI rotor, tested at the NASA Ames Research Center. Good agreement with the measurements is found. The computed results are used to develop improved engineering models for the loss of lift at the blade tip, and for the delay in the stall angle at inboard locations. The improved models are incorporated in a blade element-momentum (BEM) analysis to study the post-stall behavior of a three-bladed rotor tested at NREL.

Unsteady Analysis on the Effects of Tip Clearance Height on Hot Streak Migration Across Rotor Blade Tip Clearance

2013 ◽  
Author(s):  
Zhaofang Liu ◽  
Zhao Liu ◽  
Zhenping Feng
Keyword(s):  
Rotor Blade ◽  
High Speed ◽  
Stokes Equations ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Inlet Temperature ◽  
Leakage Flow ◽  
Blade Tip ◽  
Hot Streak ◽  
Blade Tip Clearance

This paper presents an investigation on the hot streak migration across rotor blade tip clearance in a high pressure gas turbine with different tip clearance heights. The blade geometry is taken from the first stage of GE-E3 turbine engine. Three tip clearances, 1.0%, 1.5% and 2.5% of the blade span with a flat tip were investigated respectively, and the uniform and non-uniform inlet temperature profiles were taken as the inlet boundary conditions. By solving the unsteady compressible Reynolds-averaged Navier-Stokes equations, the time dependent solutions were obtained. The results indicate that the large tip clearance intensifies the leakage flow, increases the hot streak migration rate, and aggravates the heat transfer environment on blade tip. However, the reverse secondary flow dominated by the relative motion of casing is insensitive to the change of tip clearance height. Attributed to the high-speed rotation of rotor blade and the low pressure difference between both sides of blade, a reverse leakage flow zone emerges over blade tip near trailing edge. To eliminate the effects of blade profile variation due to twist along the blade span on the aerothermal performance in tip clearance, the tested rotor (straight) blade and the original rotor (twisted) blade of GE-E3 first stage with the same tip profile are compared in this paper.

scholarly journals Investigation of Slotted Tip Parameters on the Aerodynamic Characteristic of Helicopter Rotor

2018 ◽  
Vol 36 (4) ◽  
pp. 778-784
Author(s):  
Rongqian Chen ◽  
Xu Wang ◽  
Qiyou Chen ◽  
Chengxiang Zhu ◽  
Yancheng You
Keyword(s):  
Stokes Equations ◽  
Model Simulation ◽  
Lift Coefficient ◽  
Tip Vortex ◽  
Helicopter Rotor ◽  
Power Coefficient ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Volume Method ◽  
Central Scheme

Numerical simulations are conducted to investigate the effect of helicopter rotor tip vortex alleviation using a slotted tip, and effects of parameters involving location, number, aperture of the slot on tip vortex structure and aerodynamic performance are analyzed in detail. The flow field of hovering helicopter rotor is simulated by solving Navier-Stokes equations in the rotating coordinate system. Finite volume method combined with overset unstructured grids algorithm are adopted. The calculation of inviscid fluxes uses second-order central scheme with artificial dissipation, and turbulence model utilizes Spalart-Allmaras model. Simulation results show that the location of the slot has little effect on tip vortex alleviation. The larger the number and aperture of the slot, the better the effect of slotted tips weakening tip vortex. Lift coefficient of helicopter rotor with a slotted tip increases slightly compared with that without slots, while power coefficient increases drastically.

Non-inertial multiblock Navier-Stokes calculation for hovering rotor flowfields using relative velocity approach

2001 ◽  
Vol 105 (1049) ◽  
pp. 379-389 ◽  
Author(s):  
B. Zhong ◽  
N. Qin
Keyword(s):  
Relative Velocity ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Tip Vortex ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Structured Grid ◽  
Cylindrical Grid ◽  
Relative Variable ◽  
Model Rotor

AbstractA three dimensional Navier-Stokes solver is presented for calculating the hovering rotor flowfield using Osher's approximate Riemann solver. The Navier-Stokes equations are recast in the attached blade relative system using relative flow velocities as variables. Multiblock techniques are used to obtain a structured grid around the blade. A modified MUSCL scheme is proposed to alleviate the inaccuracy in the discretisation of the relative variable formulation. The calculations are performed for a two-bladed model rotor on C-H, O-O and C-H cylindrical grid topologies respectively. Computational solutions show reasonably good agreement with the experimental data for different lifting cases. The difficulty and suitability of different grid topologies for capturing the tip vortex is illustrated. The differences between Euler and Navier-Stokes solutions and between wake modelling and wake capturing approaches are also revealed. The results indicate that the relative velocity approach can give reasonable results for hovering rotor flowfields if due care is taken in minimising possible numerical errors.

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