Measurements in the Near-Wake Region of a Slender, Self-Propelled Model at Pitch or Yaw

1983 ◽  
Vol 27 (04) ◽  
pp. 227-235 ◽  
Author(s):  
J. Schetz ◽  
H. Lee ◽  
F. Kong
Keyword(s):  
Turbulent Flow ◽  
Flow Characteristics ◽  
Wake Region ◽  
Mean Flow ◽  
Near Wake ◽  
Flow Measurements ◽  
Vertical Control ◽  
Straight Line ◽  
Head Probe ◽  
Control Surfaces

An experimental investigation of the near-wake region of a slender, propeller-driven model at pitch or yaw was undertaken in the Virginia Tech low-turbulence wind tunnel. The control surfaces on the model were set to render the model in equilibrium for the case with model pitch. The vehicle design was such that the vertical control surfaces were insufficient to achieve an equilibrium condition with the model at yaw. This is neither unusual nor undesirable, since such a vehicle can turn freely and there is little desire to operate in a straight line at yaw. A yaw-head probe was used for mean flow measurements, and a hot-wire anemometer with a normal, single wire or an X-wire served to obtain turbulent flow characteristics. The control surfaces were found to have mainly local influences on the flow field. In the pitch case, good symmetry was exhibited on both mean and turbulent flow quantities, but the lack of complete, all-directional equilibrium in the yaw case prevented the achievement of symmetry.

Highly resolved experimental results of the separated flow in a channel with streamwise periodic constrictions

2016 ◽  
Vol 796 ◽  
pp. 257-284 ◽  
Author(s):  
Christian J. Kähler ◽  
Sven Scharnowski ◽  
Christian Cierpka
Keyword(s):  
Turbulent Flow ◽  
Flow Separation ◽  
Flow Direction ◽  
Separated Flow ◽  
Mean Flow ◽  
Complex Flow ◽  
Flow Measurements ◽  
Flow Features ◽  
Wall Flow ◽  
Near Wall

The understanding and accurate prediction of turbulent flow separation on smooth surfaces is still a challenging task because the separation and the reattachment locations are not fixed in space and time. Consequently, reliable experimental data are essential for the validation of numerical flow simulations and the characterization and analysis of the complex flow physics. However, the uncertainty of the existing near-wall flow measurements make a precise analysis of the near-wall flow features, such as separation/reattachment locations and other predicted near-wall flow features which are under debate, often impossible. Therefore, the periodic hill experiment at TU Munich (ERCOFTAC test case 81) was repeated using high resolution particle image velocimetry and particle tracking velocimetry. The results confirm the strong effect of the spatial resolution on the near-wall flow statistics. Furthermore, it is shown that statistically stable values of the turbulent flow variables can only be obtained for averaging times which are challenging to realize with highly resolved large eddy simulation and direct numerical simulation techniques. Additionally, the analysis implies that regions of correlated velocity fluctuations with rather uniform streamwise momentum exist in the flow. Their size in the mean flow direction can be larger than the hill spacing. The possible impact of the correlated turbulent motion on the wake region is discussed, as this interaction might be important for the understanding and control of the flow separation dynamics on smooth bodies.

Experimental and Numerical Investigations of the 3-D Turbulent Flow Characteristics Around Submerged Permeable Breakwaters

2017 ◽  
Author(s):  
Caleb Stanley ◽  
Georgios Etsias ◽  
Steven Dabelow ◽  
Dimitrios Dermisis ◽  
Ning Zhang
Keyword(s):  
Turbulent Flow ◽  
Laboratory Experiments ◽  
Flow Characteristics ◽  
Mean Flow ◽  
Turbulent Structures ◽  
3 Dimensional ◽  
The Mean ◽  
Design Simplicity ◽  
Study Laboratory ◽  
Geometric Designs

Submerged breakwaters are favored for their design simplicity in projects intended to dissipate wave energy and reduce erosion on coastlines. Despite their popularity, the effects that submerged breakwaters exhibit on the surrounding hydrodynamics are not clearly understood, mainly due to the flow complexity generated from 3-dimensional turbulent structures in the vicinity of the breakwaters that affect the mean flow characteristics and the transport of sediment. The objective of this study was to evaluate the effects that various geometric designs of submerged permeable breakwaters have on the turbulent flow characteristics. To meet the objective of this study, laboratory experiments were performed in a water-recirculating flume, in which the 3-dimensional velocity field was recorded in the vicinity of scaled breakwater models. Breakwaters that were tested include non-permeable, three-hole, and ten-hole models. The experimental data obtained was compared to results obtained from numerical simulations. Results demonstrated that permeable breakwaters exhibit more vertical turbulent strength than their non-permeable counterparts. It was also discovered that three-hole breakwater models produce higher turbulent fluctuations than that of the ten-hole breakwaters. The results from this study will be used eventually to enhance the performance of restoration projects in coastal areas in Louisiana.

Wind Tunnel Tests on Flow Characteristics of the KRISO 3,600 TEU Containership and 300K VLCC Double-Deck Ship Models

2003 ◽  
Vol 47 (01) ◽  
pp. 24-38 ◽  
Author(s):  
Sang-Joon Lee ◽  
Hak-Rok Kim ◽  
Wu-Joan Kim ◽  
Suak-Ho Van
Keyword(s):  
Wind Tunnel ◽  
Flow Characteristics ◽  
Shear Stresses ◽  
Spatial Distributions ◽  
Wake Region ◽  
Turbulence Statistics ◽  
Near Wake ◽  
Mean Velocity ◽  
Freestream Velocity ◽  
Longitudinal Vortices

The flow characteristics in the stern and near-wake region of two ship models, the Korea Research Institute of Ships and Ocean Engineering (KRISO) 3,600 TEU containership (KCS) and the KRISO 300K very large crude oil carrier (VLCC) (KVLCC), were investigated experimentally. The double-deck ship models were installed in a subsonic wind tunnel. The freestream velocity was fixed at Uo = 25 m/s, and the corresponding Reynolds numbers based on the model length (Lpp) were about 3.3x 106 and 4.6x 106for the KCS and KVLCC models, respectively. The spatial distributions of mean velocity components and turbulence statistics, including turbulence intensities, Reynolds shear stresses, and turbulent kinetic energy, were measured using a hot-wire anemometer. For both ship models, the stern flow and near-wake show very complicated three-dimensional flow patterns. The longitudinal vortices formed in the stern region dominantly influence the flow structure in the near-wake region. In the region of main longitudinal vortices, the mean velocity deficits and all turbulence statistics have large values, compared with the surrounding flow. As the flow moves downstream, the turbulence statistics increase and have maximum values at the after-perpendicular (AP) plane and then decrease gradually due to the expansion of the shear layer. For the KVLCC model, the spatial distributions of mean velocity components and turbulence intensities behind the propeller plane clearly show hook-shaped contours. These experimental results, especially the turbulence statistics, can be used not only to understand the flows around modern practical hull forms but also to validate the computational fluid dynamics codes and turbulence models. The complete experimental data set is available on the website (http://www.postech.ac.kr/me/efml/data).

Effect of a Simulated Free Surface on the Wake of a Slender Body

1986 ◽  
Vol 30 (04) ◽  
pp. 242-255
Author(s):  
P. Mitra ◽  
W. Neu ◽  
J. Schetz
Keyword(s):  
Free Surface ◽  
Turbulent Flow ◽  
Normal Component ◽  
Image Plane ◽  
Axisymmetric Body ◽  
Transverse Component ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Flow Measurements ◽  
The Mean

Turbulent flow measurements were performed in the wake of a slender axisymmetric body in the presence of a flat plate strut and an image plane crudely representing the "rigid lid" approximation to a free surface. The tests were performed in a wind tunnel at a nominal Reynolds number of 6.0 ⨯ 105. A Yawhead probe was used for the mean flow measurements, and a Constant Temperature Anemometer System with an x-wire probe was used to obtain the turbulent flow characteristics. The presence of the image plane was found to increase the velocity defect and the static pressure as the image plane was approached. A redistribution among the various components of velocity fluctuations was noted near the image plane. The transverse component was enhanced at the expense of the normal component. The image plane also was found to influence the magnitudes and radial spread of turbulence intensities and Reynolds stresses. Some interactions between the wake of the axisymmetric body and that of the plate strut were observed. Overall, the mean velocities and the turbulence quantities indicated symmetry about the image plane throughout the wake.

Experimental Study on the Near Wake Behind Two Staggered Cylinders of Unequal Diameters

2012 ◽  
Author(s):  
Yangyang Gao ◽  
Xikun Wang ◽  
Soon Keat Tan
Keyword(s):  
Reynolds Stress ◽  
Incident Angle ◽  
Reynolds Shear Stress ◽  
Flow Characteristics ◽  
Circular Cylinders ◽  
Mean Flow ◽  
Near Wake ◽  
Particle Image Velocimetry Technique ◽  
Image Velocimetry ◽  
Spacing Ratio

The wake structure behind two staggered circular cylinders with unequal diameters was investigated experimentally using the particle image velocimetry technique (PIV). This investigation was focused on the variations of flow patterns in terms of incident angle at Reynolds number Re = 1200. Comparisons of the time-averaged flow field of two staggered cylinders with unequal diameters at different angles were made to elucidate the mean flow characteristics. The characteristics of Reynolds shear stress contours at different incident angles and spacing ratios were also investigated. The results showed that with increasing of incident angle, the scale of Reynolds stress contours behind the upstream cylinder becomes larger, as well as the effect of spacing ratio on Reynolds stress contours.

Turbulence Measurements Downstream of a Turbine Cascade at Different Incidence Angles and Pitch-Chord Ratios

1993 ◽  
Author(s):  
Vincenzo Dossena ◽  
Antonio Perdichizzi ◽  
Marina Ubaldi ◽  
Pietro Zunino
Keyword(s):  
Turbulent Flow ◽  
Reynolds Stress ◽  
Incidence Angle ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Turbine Cascade ◽  
Mean Flow ◽  
Flow Measurements ◽  
Flow Features ◽  
Turbulent Flow Structure

An experimental investigation on a linear turbine cascade has been carried out to study the effects induced by incidence angle and pitch-chord ratio variations on the three-dimensional turbulent flow downstream of the cascade. Previous mean flow measurements have shown how these parameters influence the energy losses and the secondary velocity field. Now detailed hot wire measurements have been performed on a plane located at 22 per cent of an axial chord downstream of the trailing edge, in order to determine the distribution of all the six Reynolds stress tensor components, for three incidence conditions (i = −30, 0, +30 deg) and for three pitch-chord ratios (s/c = 0.58, 0.72, 0.87). Significant changes of the turbulent flow structure, interesting magnitude and distribution of the Reynolds stress components, have been observed for all the considered test conditions. The analysis of the results shows the correlation between the mean flow features and the turbulent quantities and the relationship between the energy loss production and the blade loading variation. The presented data are also suitable for assessing the behaviour of turbulence models in complex 3D flows, on design and off-design conditions.

scholarly journals Spectral-Element Simulation of the Turbulent Flow in an Urban Environment

2021 ◽  
Author(s):  
Maxime Stuck ◽  
Alvaro Vidal ◽  
Pablo Torres ◽  
Hassan M. Nagib ◽  
Candace Wark ◽  
...  
Keyword(s):  
Turbulent Flow ◽  
Urban Environment ◽  
Good Description ◽  
Flow Behavior ◽  
Flow Characteristics ◽  
Mean Flow ◽  
Complex Flow ◽  
Turbulence Statistics ◽  
Experimental Database ◽  
The Impact

The mean flow and turbulence statistics of the flow through a simplified urban environment, which is an active research area in order to improve the knowledge of turbulent flow in cities, is investigated. This is useful for civil engineering, pedestrian comfort and for health concerns caused by pollutant spreading. In this work, we provide analysis of the turbulence statistics obtained from well-resolved large-eddy simulations (LES). A detailed analysis of this database reveals the impact of the geometry of the urban array on the flow characteristics and provides for a good description of the turbulent features of the flow within a simplified urban environment. The most prominent features of this complex flow include coherent vortical structures such as the so-called arch vortex, the horseshoe vortex and the roof vortex. These structures of the flow have been identified by an analysis of the turbulence statistics. The influence of the geometry of the urban environment (and particularly the street width and the building height) on the overall flow behavior have also been studied. Finally, the well-resolved LES results were compared with the experimental database from Monnier et al. to discuss differences and similarities between the respective urban configurations.

Interactions Between the Shear Layer Emanating From Rectangular Cylinders and the Near Wake Region

2021 ◽  
Author(s):  
Sedem Kumahor ◽  
Samuel Addai ◽  
Mark F. Tachie
Keyword(s):  
Kinetic Energy ◽  
Shear Layer ◽  
Turbulent Kinetic Energy ◽  
Leading Edge ◽  
Wake Region ◽  
Mean Flow ◽  
Near Wake ◽  
Aspect Ratios ◽  
The Mean ◽  
Rectangular Cylinders

Abstract The interactions between the separated shear layer and the near wake region of rectangular cylinders of varying streamwise extents in a uniform flow are investigated using time resolved particle image velocimetry. The streamwise aspect ratios (AR) tested were 1 and 5, and the Reynolds number based on the oncoming flow velocity and cylinder height is 16200. The effects of varying AR on the mean flow, turbulent kinetic energy and Reynolds shear stresses are studied. Furthermore, the unsteady characteristics of the separation bubbles are examined in terms of frequency spectra analysis. The mean flow topology shows flow separation at the leading edge is not affected by the streamwise aspect ratios. However, the primary, secondary and wake vortexes show significant differences. Mean flow reattaches over the cylinder at 4.30 cylinder heights in the AR5 case while there is no mean reattachment in the AR1 case. The magnitudes of turbulent kinetic energy and Reynolds shear stress in the wake region are an order of magnitude higher in AR1 compared to AR5. Depending on the streamwise location, the vortex shedding motions in the near wake region reflect the dominant and second harmonic of the shear layer shedding frequency measured near the leading edge.

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