3D Measurements of Deterministic Stresses Within a Rotor-Stator Gap at Mid-Span and Tip Regions

Volume 1 ◽  
2004 ◽  
Author(s):  
Oguz Uzol ◽  
Yi-Chih Chow ◽  
Francesco Soranna ◽  
Joseph Katz ◽  
Charles Meneveau
Keyword(s):  
Shear Stress ◽  
Normal Stress ◽  
Rotor Blade ◽  
Tip Vortex ◽  
Normal Stresses ◽  
Tip Vortices ◽  
Stress Components ◽  
Stress Levels ◽  
Order Of Magnitude ◽  
Axial Normal Stress

Stereoscopic Particle Image Velocimetry is used for measuring the distributions of the deterministic stresses, in the tip and mid-span regions, within the second stage rotor-stator gap of a two-stage axial turbomachine. This effort extends our previous two-dimensional measurements to study the dynamics of deterministic stresses in a multistage turbomachine using experimental data. All three components of the velocity vector, and all six components of both the turbulent and deterministic stress tensors are obtained at a Reynolds number of 370,000 based on the tip speed and the rotor blade chord, and in an optically unobstructed facility that uses blades and fluid with matched optical indices of refraction. Results at 50% show that although the radial velocity levels are about an order of magnitude smaller than the axial and lateral velocity levels, the flow is not exactly two-dimensional. The wake kinking phenomenon and the presence of chopped-off stator wake segments introduce three-dimensionality to the flow. The radial velocity fluctuations are high around the kink region, and get even higher when the potential field of the stator blade starts to interact with the kink zone. In general, the turbulent normal stresses are higher than the deterministic normal stresses while the turbulent and deterministic shear stress levels are in the same order of magnitude. The flow at 90% span is dominated by the tip vortices, which create high levels of non-uniformities in the distributions of all three velocity components. The tip vortex loses its structure when it gets close to the pressure side of the following rotor blade and undergoes a possible spiral-type vortex breakdown. The meandering and convection of the tip vortices contribute to the elevated levels of average-passage turbulence and deterministic stresses along the tip vortex transport direction. The deterministic axial normal stress is higher than the turbulent axial normal stress; the deterministic lateral normal stress is initially higher, but it quickly drops down to turbulent lateral normal stress levels; and the deterministic radial normal stress is initially close to turbulent radial normal stress levels, but it decays relatively quickly and becomes less than the turbulent radial normal stress levels further downstream. The deterministic shear stress components are 5 to 10 times higher than the turbulent shear stress components.

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.

Investigating the Coupled Effects Between Rotor-Blade Aeroelasticity and Tip Vortex Stability

2020 ◽  
Author(s):  
Steven N. Rodriguez ◽  
Athanasios P. Iliopoulos ◽  
John G. Michopoulos ◽  
Justin W. Jaworski
Keyword(s):  
Rotor Blade ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Tip Vortex ◽  
Tip Vortices ◽  
Operational Conditions ◽  
Vortex Stability ◽  
Blade Vortex Interaction ◽  
Wake Interactions ◽  
The Relationship

Abstract The relationship between rotor-blade aeroelasticity and tip-vortex stability is investigated numerically. An aeroelastic framework based on the free-vortex wake and finite element methods is employed to model a subscaled helicopter rotor in hover and forward-tilted conditions. A linear eigenvalue stability analysis is performed on tip vortices to associate the coupled impact of aeroelastic effects and vortex evolution. Prior numerical investigations have shown that highly flexible wind turbine rotor-blades have the potential to decrease levels of the instability of tip vortices. The present work focuses on testing these findings against a subscaled rotor within the range of helicopter operational rotation frequencies. The presented work aims to develop further insight into rotor-wake interactions and blade-vortex interaction to explore the mitigation of adverse rotorcraft operational conditions, such as their effect on aerodynamic-induced airframe vibrations and the associated life-cycle fatigue performance.

The Contrastive Research of Direct Shear Test on Different Pile-Soil Interface

2011 ◽  
Vol 90-93 ◽  
pp. 1743-1747
Author(s):  
Dong Wang ◽  
Jian Xin Zhang ◽  
Bin Tian ◽  
Jia Cao
Keyword(s):  
Shear Stress ◽  
Shear Strength ◽  
Normal Stress ◽  
Laboratory Tests ◽  
Direct Shear Test ◽  
Shear Test ◽  
Normal Stresses ◽  
Friction Resistance ◽  
Striking Change ◽  
Soil Interface

In order to discuss the friction resistance properties between pile and soil, three groups of shear laboratory tests of pile-soil interface are adopted among concrete-soil , steel-soil and plastic(HDPE)-soil, and each test applies six normal stresses. The result indicates that with the growth of normal stress, the shear strength of pile-soil are increased; under the same normal stress, there is little change in frontal parts of curve with shear stress and displacement, but the rest of curve have a striking change along with the increase of normal stress; when the normal stress is less, the shear stress of different interfaces have little change; when the normal stress is greater, it shows that the shear strength of HDPE-soil interface is the greatest.

Normal fluid stresses are prevalent in rotary ventricular assist devices: A computational fluid dynamics analysis

2018 ◽  
Vol 41 (11) ◽  
pp. 738-751 ◽  
Author(s):  
Dominica PY Khoo ◽  
Andrew N Cookson ◽  
Harinderjit S Gill ◽  
Katharine H Fraser
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Shear Stress ◽  
Normal Stress ◽  
Ventricular Assist Devices ◽  
Shear Stresses ◽  
Normal Stresses ◽  
Ventricular Assist ◽  
Assist Devices ◽  
Normal And Shear Stresses

Despite the evolution of ventricular assist devices, ventricular assist device patients still suffer from complications due to the damage to blood by fluid dynamic stress. Since rotary ventricular assist devices are assumed to exert mainly shear stress, studies of blood damage are based on shear flow experiments. However, measurements and simulations of cell and protein deformation show normal and shear stresses deform, and potentially damage, cells and proteins differently. The aim was to use computational fluid dynamics to assess the prevalence of normal stress, in comparison with shear stress, in rotary ventricular assist devices. Our calculations showed normal stresses do occur in rotary ventricular assist devices: the fluid volumes experiencing normal stress above 10 Pa were 0.011 mL (0.092%) and 0.027 mL (0.39%) for the HeartWare HVAD and HeartMate II (HMII), and normal stresses over 100 Pa were present. However, the shear stress volumes were up to two orders of magnitude larger than the normal stress volumes. Considering thresholds for red blood cell and von Willebrand factor deformation by normal and shear stresses, the fluid volumes causing deformation by normal stress were between 2.5 and 5 times the size of those causing deformation by shear stress. The exposure times to the individual normal stress deformation regions were around 1 ms. The results clearly show, for the first time, that while blood within rotary ventricular assist devices experiences more shear stress at much higher magnitudes as compared with normal stress, there is sufficient normal stress exposure present to cause deformation of, and potentially damage to, the blood components. This study is the first to quantify the fluid stress components in real blood contacting devices.

Turbulent Stresses in the Region of Aortic and Pulmonary Valves

1982 ◽  
Vol 104 (3) ◽  
pp. 238-244 ◽  
Author(s):  
P. D. Stein ◽  
F. J. Walburn ◽  
H. N. Sabbah
Keyword(s):  
Shear Stress ◽  
Normal Stress ◽  
Blood Cells ◽  
Reynolds Shear Stress ◽  
Shear Stresses ◽  
Normal Stresses ◽  
Reynolds Stresses ◽  
Aortic Valves ◽  
Hot Film

The specific features of turbulent flow that are likely to be damaging to the blood cells and platelets are the stresses which are intrinsic to turbulence, known as Reynolds stresses. These include normal stresses as well as shear stresses. The purpose of this study is to determine the magnitude of the turbulent stresses that may occur during ejection in the vicinity of normal and diseased aortic valves near normal pulmonary valves. Both Reynolds normal stresses and Reynolds shear stresses were calculated from velocities obtained in vitro with a laser Doppler anemometer in the region of two severely stenotic and regurgitant human aortic valves. Reynolds normal stresses were also calculated from velocities obtained with a hot-film anemometer in 21 patients in the region of normal and diseased aortic valves. In seven of these patients, it was calculated in the region of the normal pulmonary valve. The Reynolds normal stress in patients with combined aortic stenosis and insufficiency was prominently higher than in patients with normal valves. In the former, the Reynolds normal stress during ejection transiently reached 18,000 dynes/cm2. This was in the range of the Reynolds normal stress observed in vitro. The Reynolds shear stress measured in vitro transiently reached 11,900 dynes/cm2 during ejection. Because the Reynolds normal stresses in the presence of the severely stenotic and regurgitant valves were comparable in vitro and in patients, it is likely that the Reynolds shear stress in patients is also comparable to values measured in vitro. These values were well above the stresses which, when sustained, have been shown to have a damaging effect upon blood cells and platelets.

scholarly journals Rock Stress Measurements for Unlined Pressure Tunnels: A True Triaxial Laboratory Experiment to Investigate the Ability of a Simplified Hydraulic Jacking Test to Assess Fracture Normal Stress

2021 ◽  
Author(s):  
Henki Ødegaard ◽  
Bjørn Nilsen
Keyword(s):  
Normal Stress ◽  
Test Method ◽  
Sudden Increase ◽  
Normal Stresses ◽  
True Triaxial ◽  
Step Rate ◽  
Stress Measurements ◽  
Fracture Closure ◽  
Rate Test ◽  
Hydraulic Jacking

AbstractTo avoid hydraulic failure of unlined pressure tunnels, knowledge of minimum principal stress is needed. Such knowledge is only obtainable from in situ measurements, which are often time-consuming and relatively costly, effectively limiting the number of measurements typically performed. In an effort to enable more stress measurements, the authors propose a simplified and cost-effective stress measuring method; the Rapid Step-Rate Test (RSRT), which is based on existing hydraulic testing methods. To investigate the ability of this test to measure fracture normal stresses in field-like conditions, a true triaxial laboratory test rig has been developed. Hydraulic jacking experiments performed on four granite specimens, each containing a fracture, have been performed. Interpretation of pressure-, flow- and acoustic emission (AE) data has been used to interpret fracture behaviour and to assess fracture normal stresses. Our experimental data suggest that the proposed test method, to a satisfactory degree of reliability, can measure the magnitude of fracture normal stress. In addition, a clear correlation has been found between fracture closure and sudden increase in AE rate, suggesting that AE monitoring during testing can serve as a useful addition to the test. The rapid step-rate test is also considered relevant for field-scale measurements, with only minor adaptions. Our findings suggest that the RSRT can represent a way to get closer to the ideal of performing more testing along the entire length of pressure tunnel, and not only at key locations, which requires interpolation of stress data with varying degree of validity.

Shear strength and dilative characteristics of an unsaturated compacted completely decomposed granite soil

2010 ◽  
Vol 47 (10) ◽  
pp. 1112-1126 ◽  
Author(s):  
Md. Akhtar Hossain ◽  
Jian-Hua Yin
Keyword(s):  
Shear Strength ◽  
Normal Stress ◽  
Matric Suction ◽  
Water Retention Curve ◽  
Direct Shear ◽  
Normal Stresses ◽  
Soil Water Retention Curve ◽  
Strength Data ◽  
Decomposed Granite ◽  
Completely Decomposed Granite

Shear strength and dilative characteristics of a re-compacted completely decomposed granite (CDG) soil are studied by performing a series of single-stage consolidated drained direct shear tests under different matric suctions and net normal stresses. The axis-translation technique is applied to control the pore-water and pore-air pressures. A soil-water retention curve (SWRC) is obtained for the CDG soil from the equilibrium water content corresponding to each applied matric suction value for zero net normal stress using a modified direct shear apparatus. Shear strength increases with matric suction and net normal stress, and the failure envelope is observed to be linear. The apparent angle of internal friction and cohesion intercept increase with matric suction. A greater dilation angle is found at higher suctions with lower net normal stresses, while lower or zero dilation angles are observed under higher net normal stresses with lower suctions, also at a saturated condition. Experimental shear strength data are compared with the analytical shear strength results obtained from a previously modified model considering the SWRC, effective shear strength parameters, and analytical dilation angles. The experimental shear strength data are slightly higher than the analytical results under higher net normal stresses in a higher suction range.

Effect of Upstream Rotor Vortical Disturbances on the Time-Averaged Performance of Axial Compressor Stators: Part 1—Framework of Technical Approach and Wake–Stator Blade Interactions

1999 ◽  
Vol 121 (3) ◽  
pp. 377-386 ◽  
Author(s):  
T. V. Valkov ◽  
C. S. Tan
Keyword(s):  
Total Pressure ◽  
Axial Compressor ◽  
Tip Vortex ◽  
Technical Approach ◽  
Tip Vortices ◽  
Tip Leakage ◽  
Unsteady Interaction ◽  
Flow Approximation ◽  
Stator Blade ◽  
The Impact

In a two-part paper, key computed results from a set of first-of-a-kind numerical simulations on the unsteady interaction of axial compressor stators with upstream rotor wakes and tip leakage vortices are employed to elucidate their impact on the time-averaged performance of the stator. Detailed interrogation of the computed flow field showed that for both wakes and tip leakage vortices, the impact of these mechanisms can be described on the same physical basis. Specifically, there are two generic mechanisms with significant influence on performance: reversible recovery of the energy in the wakes/tip vortices (beneficial) and the associated nontransitional boundary layer response (detrimental). In the presence of flow unsteadiness associated with rotor wakes and tip vortices, the efficiency of the stator under consideration is higher than that obtained using a mixed-out steady flow approximation. The effects of tip vortices and wakes are of comparable importance. The impact of stator interaction with upstream wakes and vortices depends on the following parameters: axial spacing, loading, and the frequency of wake fluctuations in the rotor frame. At reduced spacing, this impact becomes significant. The most important aspect of the tip vortex is the relative velocity defect and the associated relative total pressure defect, which is perceived by the stator in the same manner as a wake. In Part 1, the focus will be on the framework of technical approach, and the interaction of stator with the moving upstream rotor wakes.

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