scholarly journals Impact of Surface Roughness on the Turbulent Wake Flow of a Turbine Blade

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
K. Mulleners ◽  
P. Gilge ◽  
S. Hohenstein
Keyword(s):  
Surface Roughness ◽  
Velocity Field ◽  
Turbine Blade ◽  
Field Measurements ◽  
Wake Flow ◽  
Vortical Structures ◽  
Image Velocimetry ◽  
Stereo Particle Image Velocimetry ◽  
The Individual ◽  
The Impact

Roughened aeroengine blade surfaces lead to increased friction losses and reduced efficiency of the individual blades. The surface roughness also affects the wake flow of the blade and thus the inflow conditions for the subsequent compressor or turbine stage. To investigate the impact of surface roughness on a turbulent blade wake, we conducted velocity field measurements by means of stereo particle image velocimetry in the wake of a roughened turbine blade in a linear cascade wind tunnel. The turbine blade was roughened at different chordwise locations. The influence of the chordwise location of the added surface roughness was examined by comparing their impact on the width and depth of the wake and, the positions and distribution of vortical structures in the wake. Additionally, the friction loss coefficients for different surface roughness positions were estimated directly from the velocity field.

Experimental Study of Large-Scale Flow Structures in an Aneurysm

2018 ◽  
Author(s):  
Paulo Yu ◽  
Vibhav Durgesh
Keyword(s):  
Large Scale ◽  
Flow Structures ◽  
Pump System ◽  
Vortical Structures ◽  
Abnormal Growth ◽  
Image Velocimetry ◽  
Large Scale Flow ◽  
The Impact ◽  
Inflow Conditions ◽  
Aneurysm Model

An aneurysm is an abnormal growth in the wall of a weakened blood vessel, and can often be fatal upon rupture. Studies have shown that aneurysm shape and hemodynamics, in conjunction with other parameters, play an important role in growth and rupture. The objective of this study was to investigate the impact of varying inflow conditions on flow structures in an aneurysm. An idealized rigid sidewall aneurysm model was prepared and the Womersley number (α) and Reynolds number (Re) values were varied from 2 to 5 and 50 to 250, respectively. A ViVitro Labs pump system was used for inflow control and Particle Image Velocimetry was used for conducting velocity measurements. The results showed that the primary vortex path varied with an increase in α, while an increase in Re was correlated to the vortex strength and formation of secondary vortical structures. The evolution and decay of vortical structures were also observed to be dependent on α and Re.

Analysis of Particle Image Velocimetry Measurements of Natural Convection in an Enclosure Using Proper Orthogonal Decomposition

2015 ◽  
Vol 137 (12) ◽  
Author(s):  
Nirmalendu Biswas ◽  
Souvick Chatterjee ◽  
Mithun Das ◽  
Amlan Garai ◽  
Prokash C. Roy ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Natural Convection ◽  
Velocity Field ◽  
Proper Orthogonal Decomposition ◽  
Particle Image ◽  
Field Measurements ◽  
Orthogonal Decomposition ◽  
Image Velocimetry ◽  
Low Dimensional ◽  
Proper Orthogonal

This work investigates natural convection in an enclosure with localized heating on the bottom wall with a flushed or protruded heat source and cooled on the top and the side walls. Velocity field measurements are done by using 2D particle image velocimetry (PIV) technique. Proper orthogonal decomposition (POD) has been used to create low dimensional approximations of the system for predicting the flow structures. The POD-based analysis reveals the modal structure of the flow field and also allows reconstruction of velocity field at conditions other than those used in PIV study.

Experimental Investigation of the Wake of a Discontinuous Cylinder

2010 ◽  
Author(s):  
V. S. R. Mandava ◽  
Gregory A. Kopp ◽  
Joan Herrero ◽  
Francesc Giralt
Keyword(s):  
Structural Characteristics ◽  
Dominant Role ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Near Wake ◽  
Vortical Structures ◽  
Image Velocimetry ◽  
Entrainment Process ◽  
Thin Steel Plate

The effects of a discontinuous cylinder geometry on the near wake structures was investigated experimentally. This ‘discontinuous’ circular cylinder has gaps so that solid segments 5D long are followed by gaps 2.5D long, in a repeating pattern, where D is the diameter of the cylinder. A thin steel plate was used to hold all of the cylinder pieces together. Thus, a three-dimensional (3D) wake was created at the origin with the intent to force the near wake flow to have similar structural characteristics as the far wake behind an ‘infinite/continuous’ cylinder, i.e., a near wake flow with horseshoes or double rollers formed by rapid kinking of Ka´rma´n-like vortices. Since the kinetic energy associated with the fluctuations of these near-wake 3D vortical structures is high, the flow system is considered suitable to clarify the role of these velocity patterns in the entrainment process of wake flows, which is still the subject of controversy. Particle Image Velocimetry (PIV) and Hot-Wire Anemometry (HWA) techniques were used to analyze the flow at two Reynolds numbers, Re = 10000 and 4000, in the wake of the discontinuous cylinder up to x/D = 190 downstream. The development of double rollers resulting from the interaction between the high momentum flow through the gaps and the Ka´rma´n-like vortices formed behind the solid cylindrical segments was confirmed. The Strouhal number of the double rollers in the wake is 0.14. These vortices have a dominant role in the initial wake growth. Thus, the overall flow dynamics are similar to the momentum transfer that takes place at the scale of the intermittent turbulent bulges that protrude from the wake in the far region and that were reported to be associated with double rollers.

scholarly journals Measurement of the Flow Field Generated by Multicopter Propellers

Sensors ◽  
2020 ◽  
Vol 20 (19) ◽  
pp. 5537
Author(s):  
Zbigniew Czyż ◽  
Paweł Karpiński ◽  
Wit Stryczniewicz
Keyword(s):  
Velocity Field ◽  
Particle Image ◽  
Angle Of Attack ◽  
Vertical Plane ◽  
Airflow Velocity ◽  
Field Distributions ◽  
Image Velocimetry ◽  
Plane Passing ◽  
The Impact ◽  
Qualitative Analyses

This paper presents the results of research on the airflow around a multirotor aircraft. The research consisted of the analysis of the velocity field using particle image velocimetry. Based on the tests carried out in a wind tunnel, the distribution of the velocity and its components in the vertical plane passing through the propeller axis were determined for several values of the angle of attack of the tested object for two values of airflow velocity inside the tunnel, i.e., vwt = 0 m/s and vwt = 12.5 m/s. Determining the velocity value as a function of the coordinates of the adopted reference system allowed for defining the range of impact of the horizontal propellers and the fuselage of the research object itself. The tests allowed for quantitative and qualitative analyses of the airflow through the horizontal rotor. Particular attention was paid to the impact of the airflow and the angle of attack on the obtained velocity field distributions.

scholarly journals Numerical and experimental analysis of the velocity field of air flowing through swirl diffusers

2019 ◽  
Vol 128 ◽  
pp. 05003
Author(s):  
Marek Borowski ◽  
Michał Karch ◽  
Rafał Łuczak ◽  
Piotr Życzkowski ◽  
Marek Jaszczur
Keyword(s):  
Velocity Field ◽  
Ventilation System ◽  
Field Measurements ◽  
Operating Conditions ◽  
Heating And Cooling ◽  
Piv Method ◽  
Air Supply ◽  
Image Velocimetry ◽  
Comparison Of The Results ◽  
Design And Practice

The air swirl diffusers are popular for the ceiling level air supply system and have been widely used for Indoor Air Quality. They are nowadays one of the most popular diffusers commonly used in airconditioning systems [1, 2]. The swirl diffusers are intended to use in low- and medium-pressure ventilation systems. They allow for obtaining the swirl airflow and are especially recommended to use in spaces with the height from 3m up to 12m, where heating and cooling is performed by the ventilation system and where the exact setting of supply air velocity is important [3-6]. In the case of swirl diffusers,fluid flow is usually significantly influenced by the characteristics of different diffuser designs. In the ventilation system design phase, a typically focus on ventilation effectiveness and takes into account a large number of parameter. However, the discrepancy between design and practice are often experienced mainly because operating conditions don’t correspond to the designing conditions [7-9]. Inthis work, the airflow of swirl diffuser has been studied using Particle Image Velocimetry (PIV) method to analyse the mean airflow and geometry influence on the results. The paper presents a comparison of the results of velocity field measurements using the PIV method and the results obtained by means ofnumerical analysis CFD. Based on the analysis the velocity flow field was evaluated and the range of effective operation of the diffuser have been determined [10].

scholarly journals Stereo Particle Image Velocimetry Measurements of the Wake Fields Behind A Panamax Bulker Ship Model Under the Ballast Condition

2020 ◽  
Vol 8 (6) ◽  
pp. 397 ◽  
Author(s):  
Tiecheng Wu ◽  
Wanzhen Luo ◽  
Dapeng Jiang ◽  
Rui Deng ◽  
Yulong Li
Keyword(s):  
Particle Image Velocimetry ◽  
Free Surface ◽  
Velocity Fluctuation ◽  
Particle Image ◽  
Wake Flow ◽  
Reynolds Stresses ◽  
Ship Model ◽  
Image Velocimetry ◽  
Stereo Particle Image Velocimetry ◽  
Turbulent Velocity Fluctuation

Particle image velocimetry is applied in this study to measure the wake flow field of a Panamax Bulker ship model under the ballast condition. This investigation revealed that the Froude number is 0.167. The time-averaged velocity, turbulent fluctuations, turbulent kinetic energy (TKE), Reynolds stresses, and vorticity information were measured to perform a comparison with the design condition. The time-averaged velocity contours indicated that the ballast and design conditions have distinct hook-like axial velocity contours; however, they appeared at different positions. The big difference under the ballast condition is that the top of the propeller disk area is near the free surface and a region with strong root mean square velocity fluctuation is formed near the free surface. The TKE, the Reynolds stresses, and the hub cap vortex (Hcv) are all affected by the turbulent velocity fluctuation region under the ballast condition. A strong bilge vortex (Bv) is produced when the water flows through the U-shaped stern for the design and ballast conditions.

scholarly journals The nature of the vortical structures in the near wake of the Ahmed body

2017 ◽  
Vol 231 (9) ◽  
pp. 1239-1244 ◽  
Author(s):  
James Venning ◽  
David Lo Jacono ◽  
David Burton ◽  
Mark C Thompson ◽  
John Sheridan
Keyword(s):  
Water Channel ◽  
Field Measurements ◽  
The Body ◽  
Wake Flow ◽  
Generic Model ◽  
Toroidal Vortex ◽  
Near Wake ◽  
Slant Angle ◽  
Vortical Structures ◽  
Ahmed Body

This study presents the results from high-spatial-resolution water-channel velocity-field measurements behind an Ahmed body with 25° rear slant angle. The Ahmed body represents a simplified generic model of a hatchback automobile that has been widely used to study near-wake flow dynamics. The results help clarify the unresolved question of whether the time-mean near-wake flow structure is topologically equivalent to a toroidal vortex or better described by a pair of horizontally aligned horseshoe vortices, with their legs pointing downstream. The velocimetry data presented allows the tracking of the vortical structures throughout the near wake through a set of orthogonal planes, as well as the measurement of their circulation. The spanwise vortices that form as the flow separates from the top and bottom rear edges are shown to tilt downstream at the sides of the body, while no evidence is found of a time-mean attached toroidal vortex, at least for the Reynolds number (based on the square root of the frontal area) of [Formula: see text] under consideration.

Velocity field measurements in a rectangular conduit with particle image velocimetry

2007 ◽  
Vol 75 (9) ◽  
pp. 833-838 ◽  
Author(s):  
Román Martino ◽  
Agnes Paterson ◽  
Marcelo F. Piva
Keyword(s):  
Particle Image Velocimetry ◽  
Velocity Field ◽  
Particle Image ◽  
Field Measurements ◽  
Image Velocimetry

scholarly journals Vortex identification methods applied to wind turbine tip vortices

2021 ◽  
Author(s):  
Rodrigo Soto-Valle ◽  
Stefano Cioni ◽  
Sirko Bartholomay ◽  
Marinos Manolesos ◽  
Christian Navid Nayeri ◽  
...  
Keyword(s):  
Velocity Field ◽  
Wind Turbine ◽  
Tip Vortex ◽  
Vortex Center ◽  
Vortex Identification ◽  
Tip Vortices ◽  
Identification Methods ◽  
Image Velocimetry ◽  
The Impact ◽  
Selection Of

Abstract. This study describes the impact of postprocessing methods on the calculated parameters of tip vortices of a wind turbine model when tested using Particle Image Velocimetry (PIV). Several vortex identification methods and differentiation schemes are compared. The chosen methods are based on two components of the velocity field and its derivatives. They are applied to each instantaneous velocity field from the dataset and also to the calculated average velocity field. The methodologies are compared through the vortex center location, vortex core radius and jittering zone. Results show that the tip vortex center locations and radius have good comparability and can vary only a few grid spacings between methods. Conversely, the convection velocity and the jittering surface, defined as the area where the instantaneous vortex centers are located, vary between identification methods. Overall, the examined parameters depend significantly on the post-processing method and selected vortex identification criteria. Therefore, this study proves that the selection of the most suitable postprocessing methods of PIV data is pivotal to ensure robust results.

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