Flow Structures above the Trunk Deck of Sedan-Type Vehicles and Their Influence on High-Speed Vehicle Stability 1st Report: On-Road and Wind-Tunnel Studies on Unsteady Flow Characteristics that Stabilize Vehicle Behavior

2009 ◽  
Vol 2 (1) ◽  
pp. 138-156 ◽  
Author(s):  
Yoshihiro Okada ◽  
Takahide Nouzawa ◽  
Takaki Nakamura ◽  
Satoshi Okamoto
Keyword(s):  
Wind Tunnel ◽  
Unsteady Flow ◽  
High Speed ◽  
Flow Characteristics ◽  
Flow Structures ◽  
Vehicle Stability ◽  
High Speed Vehicle

scholarly journals Flow structures above the t r u n k deck of sedan-type vehicles and their influence on high-speed vehicle stability

2009 ◽  
Vol 29-1 (1) ◽  
pp. 27-27
Author(s):  
Yusuke AKIYAMA ◽  
Takahide NOUZAWA ◽  
Takaki NAKAMURA ◽  
Satoshi OKAMOTO ◽  
Yoshihiro OKADA
Keyword(s):  
High Speed ◽  
Flow Structures ◽  
Vehicle Stability ◽  
High Speed Vehicle

Multi-Angular Flame Measurements and Analysis in a Supersonic Wind Tunnel Using Fiber Based Endoscopes

2015 ◽  
Author(s):  
Lin Ma ◽  
Andrew J. Wickersham ◽  
Wenjiang Xu ◽  
Scott J. Peltier ◽  
Timothy M. Ombrello ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Thermal Management ◽  
High Speed ◽  
Flow Structures ◽  
Data Sets ◽  
Propulsion Systems ◽  
Supersonic Wind Tunnel ◽  
Optical Access ◽  
Equipment Cost ◽  
Pod Analysis

This paper reports new measurements and analysis made in the Research Cell 19 supersonic wind-tunnel facility housed at the Air Force Research Laboratory. The measurements include planar chemiluminescence from multiple angular positions obtained using fiber based endoscopes (FBEs) and the accompanying velocity fields obtained using particle image velocimetry (PIV). The measurements capture the flame dynamics from different angles (e.g., the top and both sides) simultaneously. The analysis of such data by proper orthogonal decomposition (POD) will also be reported. Non-intrusive and full-field imaging measurements provide a wealth of information for model validation and design optimization of propulsion systems. However, it is challenging to obtain such measurements due to various implementation difficulties such as optical access, thermal management, and equipment cost. This work therefore explores the application of FBEs for non-intrusive imaging measurements in supersonic propulsion systems. The FBEs used in this work are demonstrated to overcome many of the practical difficulties and significantly facilitate the measurements. The FBEs are bendable and have relatively small footprints (compared to high-speed cameras), which facilitates line-of-sight optical access. Also, the FBEs can tolerate higher temperatures than high-speed cameras, ameliorating the thermal management issues. Lastly, the FBEs, after customization, can enable the capture of multiple images (e.g., images of the flowfields at multi-angles) onto the same camera chip, greatly reducing the equipment cost of the measurements. The multi-angle data sets, enabled by the FBEs as discussed above, were analyzed by POD to extract the dominating flame modes when examined from various angular positions. Similar analysis was performed on the accompanying PIV data to examine the corresponding modes of the flowfields. The POD analysis provides a quantitative measure of the dominating spatial modes of the flame and flow structures and is an effective mathematical tool to extract key physics from large data sets such as the high-speed measurements collected in this study. However, past POD analysis has been limited to data obtained from one orientation only. The availability of data at multiple angles in this study is expected to provide further insights into the flame and flow structures in high-speed propulsion systems.

Multi-angular Flame Measurements and Analysis in a Supersonic Wind Tunnel Using Fiber-Based Endoscopes

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Lin Ma ◽  
Andrew J. Wickersham ◽  
Wenjiang Xu ◽  
Scott J. Peltier ◽  
Timothy M. Ombrello ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Thermal Management ◽  
High Speed ◽  
Flow Fields ◽  
Flow Structures ◽  
Data Sets ◽  
Propulsion Systems ◽  
Supersonic Wind Tunnel ◽  
Equipment Cost ◽  
Pod Analysis

This paper reports new measurements and analysis made in the Research Cell 19 supersonic wind-tunnel facility housed at the Air Force Research Laboratory. The measurements include planar chemiluminescence from multiple angular positions obtained using fiber-based endoscopes (FBEs) and the accompanying velocity fields obtained using particle image velocimetry (PIV). The measurements capture the flame dynamics from different angles (e.g., the top and both sides) simultaneously. The analysis of such data by proper orthogonal decomposition (POD) will also be reported. Nonintrusive and full-field imaging measurements provide a wealth of information for model validation and design optimization of propulsion systems. However, it is challenging to obtain such measurements due to various implementation difficulties such as optical access, thermal management, and equipment cost. This work therefore explores the application of the FBEs for nonintrusive imaging measurements in the supersonic propulsion systems. The FBEs used in this work are demonstrated to overcome many of the practical difficulties and significantly facilitate the measurements. The FBEs are bendable and have relatively small footprints (compared to high-speed cameras), which facilitates line-of-sight optical access. Also, the FBEs can tolerate higher temperatures than high-speed cameras, ameliorating the thermal management issues. Finally, the FBEs, after customization, can enable the capture of multiple images (e.g., images of the flow fields at multi-angles) onto the same camera chip, greatly reducing the equipment cost of the measurements. The multi-angle data sets, enabled by the FBEs as discussed above, were analyzed by POD to extract the dominating flame modes when examined from various angular positions. Similar analysis was performed on the accompanying PIV data to examine the corresponding modes of the flow fields. The POD analysis provides a quantitative measure of the dominating spatial modes of the flame and flow structures, and is an effective mathematical tool to extract key physics from large data sets as the high-speed measurements collected in this study. However, the past POD analysis has been limited to data obtained from one orientation only. The availability of data at multiple angles in this study is expected to provide further insights into the flame and flow structures in high-speed propulsion systems.

Investigation of Unsteady Flow Characteristics in Axial Rim Seal

2021 ◽  
Author(s):  
Lei Xie ◽  
Qiang Du ◽  
Guang Liu ◽  
Zengyan Lian ◽  
Ran Ren
Keyword(s):  
Unsteady Flow ◽  
Pressure Distribution ◽  
Flow Rate ◽  
Flow Characteristics ◽  
Correlation Method ◽  
Flow Structures ◽  
Rotating Speed ◽  
Hot Gas ◽  
Ansys Cfx ◽  
Large Flow

Abstract Unsteady flow structures have been observed and reported in a number of recent rim-sealing investigations. These unsteady flow structures will influence the cavity pressure distribution, therefore influence the sealing efficiency. As a result, it is important to determine the mechanisms of these unsteady flow structures and how they influence the hot gas ingestion and sealing efficiency. A two-sector axial rim seal model is used to carry out the numerical investigation. The simulation is performed using the URANS method by the commercial CFD code ANSYS CFX, in which the SST turbulent model is applied. The mechanism and influence of the unsteady flow structures are analyzed. It was found that two different types of unsteadiness are observed inside the wheel space cavity: radial large flow structures dominated by the mainstream pressure distribution and inertia wave, and circumferential Kelvin-Helmholtz vortexes induced by circumferential velocity discontinuous distribution. The number and rotating speed of the radial and circumferential flow structures can be calculated using a cross-correlation method, and it was found that they can lead to a deeper ingress. By increasing the sealing flow rate, the pressure fluctuation inside the wheel space cavity is suppressed and the rotating speed of the flow structures is deaccelerated; thus, the sealing flow stabilizes the flow inside the wheel space cavity. Meanwhile, the K-H vortices’ position is lifted by the increased sealing flow rate, and the strength of the K-H vortices is suppressed, thus the sealing efficiency inside the wheel space cavity is also improved.

Development of Large Intermittent Wind Tunnels

1955 ◽  
Vol 59 (532) ◽  
pp. 259-278 ◽  
Author(s):  
J. Lukasiewicz
Keyword(s):  
Mach Number ◽  
Wind Tunnel ◽  
Mass Flow ◽  
High Speed ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Wind Tunnels ◽  
Number Range ◽  
Pressure Storage ◽  
Vacuum Storage

SummaryTwo types of intermittent wind tunnel drives, the pressure storage drive(with atmospheric exhaust) and the vacuum storage drive (with atmospheric inlet), are examined and found to match well the tunnel pressure ratio-mass flow characteristics over a wide Mach number range (0 to 4). The design of components of intermittent wind tunnel installations, their operation and instrumentation are then considered in some detail. In order to increase the output of intermittent wind tunnels to a level comparable to that of continuously running tunnels, it is proposed to drive the models during each tunnel run through a range of incidence. This technique is at present under development in the National Aeronautical Establishment's High Speed Aerodynamics Laboratory and results so far obtained are discussed. Two tunnels are considered as examples of large intermittent installations: a 4 ft. square pressure-driven tunnel and a 6 ft. square vacuum-driven tunnel. The former is found to be a more compact and economical installation. Relative merits of continuous and intermittent installations are discussed.

Unsteady flow structures in the wake of a high-speed train

2018 ◽  
Vol 98 ◽  
pp. 381-396 ◽  
Author(s):  
Chao Xia ◽  
Hanfeng Wang ◽  
Di Bao ◽  
Zhigang Yang
Keyword(s):  
Unsteady Flow ◽  
High Speed ◽  
Flow Structures ◽  
High Speed Train

Development of a Wind Tunnel Test Apparatus for Horizontal Axis Wind Turbine Rotor Testing

2008 ◽  
Author(s):  
Michael McWillam ◽  
David Johnson
Keyword(s):  
Wind Tunnel ◽  
Wind Turbine ◽  
Wind Turbines ◽  
High Speed ◽  
Turbine Rotor ◽  
Dynamic Stall ◽  
Flow Structures ◽  
Horizontal Axis Wind Turbine ◽  
Wind Turbine Rotor ◽  
Blade Geometry

The engineering of wind turbines is not fully mature. There are still phenomena, particularly dynamic stall that cannot be accurately modeled. Dynamic stall contributes to fatigue stress and premature failure in many turbine components. The three dimensionality of dynamic stall make these structures unique for wind turbines. Currently flow visualization of dynamic stall on a wind turbine rotor has not been achieved, but these visualizations can reveal a great deal about the structures that contribute to dynamic stall. Particle Image Velocimetry (PIV) is a powerful experimental technique that can take non-intrusive flow measurements of planar flow simultaneously. High-speed cameras enable time resolved PIV can reveal the transient development. This technique is suited to gain a better understanding of dynamic stall. A custom 3.27 m diameter wind turbine has been built to allow such measurements on the blade. The camera is mounted on the hub and will take measurements within the rotating domain. Mirrors are used so that laser illumination rotates with the blade. The wind turbine will operate in controlled conditions provided by a large wind tunnel. High-speed pressure data acquisition will be used in conjunction with PIV to get an understanding of the forces associated with the flow structures. Many experiments will be made possible by this apparatus. First the flow structures responsible for the forces can be identified. Quantitative measurements of the flow field will identify the development of the stall vortex. The quantified flow structures can be used to verify and improve models. The spatial resolution of PIV can map the three dimensional structure in great detail. The experimental apparatus is independent of the blade geometry; as such multiple blades can be used to identify the effect of blade geometry. Finally flow control research in the field of aviation can be applied to control dynamic stall. These experiments will be subject of much of the future work at the University of Waterloo. Potentially this work will unlock the secrets of dynamic stall and improve the integrity of wind turbines.

Flow Characteristics Within and Downstream of a Single Shallow Cylindrical and Spherical Dimple: Effect of Pre-Dimple Boundary Layer Thickness

2005 ◽  
Author(s):  
Artem Khalatov ◽  
Aaron Byerley ◽  
Robert Vincent
Keyword(s):  
Boundary Layer ◽  
Unsteady Flow ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Bulk Flow ◽  
Flow Structures ◽  
Flow Speeds ◽  
Flow Oscillations

The objective of this study is to investigate the details of the average and unsteady flow structures in front, inside and after shallow (h/D = 0.1) spherical and cylindrical dimples placed on a flat plate at the different distances with different pre-dimple boundary layer thicknesses. The dimple projected (surface) diameter was 50.8 mm with the dimple centers located at 88 mm and 264 mm downstream of the elliptical leading edge of the flat plate. Experimental program was established in the U.S. Air Force Academy water tunnel, both dimple configurations were tested across the range of freestream water velocities from 0.07 to 0.52 m/s corresponding with diameter based Reynolds numbers ReD ranging from 3,200 to 23,500. The length based Reynolds number Rex ranged from 3,940 to 110,450 while the non-dimensional boundary layer thickness δ0/h ranged from 0.28 to 1.18. The inlet flow turbulence was below 1% at all flow speeds. Laminar flow existed upstream of the dimple for all of the flow conditions studied. Flow visualizations were performed inside and downstream of each dimple at 10 to 13 different flow speeds. All recordings were made with a SONY-DCR VX2000 video camera. Five different colors of dye were injected through five cylindrical ports, 1.0 mm in diameter, positioned at locations upstream and inside the dimples. Adobe Premiere 6.5 software was used to analyze the flow characteristics using the slow motion feature. LDV measurements were made both in front of and downstream of the dimple. The results presented include the vortex patterns, in-dimple separation zone extent, unsteady flow phenomena (bulk flow oscillations), velocity profiles after the dimple, and some features of the laminar-turbulent flow transition downstream of a single cylindrical dimple. The data obtained revealed three-dimensional and unsteady flow structures inside and downstream of the dimples, the important role of the pre-dimple boundary layer thickness. Increasing the δ0/h ratio reduces the downstream bulk flow oscillations at very low Reynolds numbers. However, at ReD>16,500 for the cylindrical dimple and at ReD>24,000 for the spherical dimple the boundary layer thickness had little effect on the bulk flow oscillations. A comparison of both spherical and cylindrical dimple geometric configurations was made to assess their relative benefits.

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