Effects of Co-Rotating Longitudinal Vortices on Turbulent Structures in the Leg of the Horseshoe Vortex

2011 ◽  
Author(s):  
Shinji Honami ◽  
Masaharu Andoh ◽  
Satoshi Tanabe ◽  
Masahiro Motosuke
Keyword(s):  
Vortex Generator ◽  
Horseshoe Vortex ◽  
Interaction Process ◽  
Longitudinal Vortex ◽  
Clear Understanding ◽  
Hot Wire ◽  
Turbulent Structures ◽  
Key Technology ◽  
Longitudinal Vortices ◽  
Stress Profiles

Manipulation of the horseshoe vortex is a key technology for improvement of blade performance in the turbine blade passage, since the complicated interaction process of the vortices occurs around the blade. The target of the present study is to clarify the interaction process between the leg vortex of the horseshoe vortex produced by the blade and the longitudinal vortex produced by the vortex generator. The arrangement of the vortex generator wings which correspond to Common Flow Down configuration is discussed. The effect of the spacing of the longitudinal vortices is also tested. The narrow and wide spacing results in the different longitudinal vortex location at the top or side of the horseshoe vortex. The measurement by the hot wire anemometer which has an X-type rotating prong by a stepping motor provides three components of the velocity and the detailed turbulence kinetic energy and the Reynolds stress profiles giving the clear understanding of the complicated interaction process of the two vortices. The narrow spacing of the longitudinal vortex in Common Flow Down configuration shows the strong interaction of the horseshoe vortex and longitudinal vortex dynamics.

The Interaction Between Horseshoe Vortex and Longitudinal Vortices From the Vortex Generators

2010 ◽  
Author(s):  
Masaharu Andoh ◽  
Masahiro Motosuke ◽  
Shinji Honami
Keyword(s):  
Reynolds Number ◽  
Strong Dependence ◽  
Three Dimensional ◽  
Horseshoe Vortex ◽  
Vortex Generators ◽  
Longitudinal Vortex ◽  
Momentum Thickness ◽  
Turbine Cascade ◽  
Hot Wire ◽  
Longitudinal Vortices

A horseshoe vortex at the blade-endwall junction introduces the reduction of turbine blade performance due to the three dimensional separation near the stagnation point of the blade and the interaction of the two legs of the horseshoe vortex in the turbine cascade passage. In order to simulate the interaction of the leg vortices in the passage, a pair of vortex generators which produces the longitudinal vortices from the tip of the generator wings is installed upstream of the blade. The experiments are made under the different configuration of the longitudinal vortex generators. NACA 0024 airfoil at zero angle of attack is used as the blade in the wind tunnel where the undisturbed momentum thickness Reynolds number is 1700. The detailed measurements on the three-components of time-averaged and fluctuated velocities are conducted by a small size of rotating X-probe hot-wire anemometer with a miniature stepping motor at the prong. The location of the leg of the horseshoe vortex can be controlled by changing the spacing of the longitudinal vortex generators. The strong dependence of the spacing of the longitudinal vortex generators on the profiles of Reynolds stress and the temporal velocity is clarified.

Numerical and Experimental Investigations on Longitudinal Vortex Generator for Heat Transfer Enhancement in Rectangular Channel

2017 ◽  
Author(s):  
Zheng Li ◽  
Zhaoqing Ke ◽  
Kuojiang Li ◽  
Xianchen Xu ◽  
Yangyang Chen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Rectangular Channel ◽  
Vortex Generator ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Longitudinal Vortex ◽  
Experimental Investigations ◽  
Transfer Enhancement ◽  
Longitudinal Vortices

In this article, longitudinal vortex generator (LVG) for heat transfer enhancement in rectangular channel is investigated numerically and experimentally. Two symmetrical delta shaped plates are placed vertically at the bottom of a rectangular channel and a pair of longitudinal vortices are generated and transferred downstream. These vortices were clockwise and counterclockwise, respectively. Correspondingly, the flow has the tendency to shoot to the surface opposite to the one with the LVG, then it separates into two steams and runs back to the LVG surface. Local heat transfer enhancement in the rectangular channel varies due to this fountain effect. Size effects were discussed for two types of LVG. With the same height, the wider LVG has better thermal performance within the rectangular geometry limit. One specific LVG was fabricated and tested experimentally and results show significant heat transfer enhancement. It indicated that the LVG can enhance the heat transfer significantly and the numerical results are reliable.

Heat Transfer Performance of Finless Flat Tube Heat Exchanger With Vortex Generator

2010 ◽  
Author(s):  
Hajime Onishi ◽  
Haruka Yonekura ◽  
Yukio Tada ◽  
Akira Takimoto
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Vortex Shedding ◽  
Heat Transfer Performance ◽  
Vortex Generator ◽  
Longitudinal Vortex ◽  
Transfer Performance ◽  
Flat Tube ◽  
Longitudinal Vortices ◽  
Tube Heat Exchanger

As the longitudinal vortex is known to be effective in enhancing heat transfer, a three-dimensional unsteady numerical analysis has been made especially for the flow and thermal fields in a unit element of flat tube heat exchanger with vortex generator (VG) in so-called middle Reynolds number range. Both staggered and in-lined arrangements of the tubes with VG are considered and results obtained from the case with VG are compared with those without VG. The study was aimed at the influence of Reynolds number and some geometrical parameters on the heat transfer and the pressure drop. Moreover, as little research has been considered the interaction between transverse vortices and longitudinal vortices in the literatures, the effect is also investigated. It is found that the longitudinal vortex plays an important role in enhancing the local heat transfer by exchanging the fluid from the tube surface region to the fresh fluid of the main flow region and lasts over long distances. Moreover, the longitudinal vortices restrain unsteady transverse vortex shedding. As a result, heat transfer rate for the flat tube with VG case is larger compared to that without VG case. From the view point of pressure drop, increase in pressure drop for the case with VG is not so much larger due to the restraint of transverse vortex shedding. Finally, heat transfer performance becomes higher for the flat tube with VG case compared to that without VG case for the same pumping power.

Heat Transfer and Flow Characteristics Due to Interaction of Longitudinal Vortices by Vortex Generator Array

2007 ◽  
Author(s):  
Daisuke Sugisaki ◽  
Masahiro Motosuke ◽  
Shinji Honami
Keyword(s):  
Heat Transfer ◽  
Test Section ◽  
Flat Surface ◽  
Flow Characteristics ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Longitudinal Vortex ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Longitudinal Vortices

This paper describes the turbulent heat transfer and the flow characteristics of the longitudinal vortices downstream of vortex generator array on the flat surface. Understanding on the heat transfer and flow characteristics is strongly required from the viewpoint of the heat transfer enhancement in an actual turbine blade design. The experiment was conducted in the test section of the wind tunnel which had a rectangular cross section and length of 2000mm. The reference velocity at the test section was 16 m/s and Reynolds number based on the momentum thickness was 1670. An array of the vortex generators with equal and/or unequal wing height was installed in the turbulent boundary layer. The experiments of the heat transfer on the flat surface were conducted by using the temperature sensitive liquid crystal. The surface of the test section was heated electrically by a thin stainless steel foil. The calibration of the hue of the liquid crystal and temperature was made by Neural Network method. Nusselt number corresponding to the turbulent heat transfer downstream of the array of the vortex generators is strongly affected by the longitudinal vortex motion. The local heat transfer depends on arrangement of the unequal wings of the vortex generator in co-rotating configuration. It is quite interesting that the longitudinal vortex located in the region of downwash motion of the adjacent vortex plays an important role in the merging process of the vortices. In conclusion, the array of the vortex generators is an effective device which can control the heat transfer and flow characteristics in the actual turbine blade cooling design.

scholarly journals Features of air flow and heat transfer control behind a backward-facing step using a vortex generator pair

2021 ◽  
Vol 2057 (1) ◽  
pp. 012011
Author(s):  
V I Terekhov ◽  
A Yu Dyachenko ◽  
V L Zhdanov ◽  
Ya J Smulsky ◽  
K A Sharov
Keyword(s):  
Heat Transfer ◽  
Thermal Characteristics ◽  
Vortex Generator ◽  
Longitudinal Vortex ◽  
Recirculation Region ◽  
Separation Region ◽  
Backward Facing Step ◽  
Longitudinal Vortices ◽  
Flow And Heat Transfer ◽  
Thermohydraulic Efficiency

Abstract The paper presents experimental results on the study of flow dynamics and heat transfer in the separation region behind the backward-facing step with longitudinal vortex generators (VG) installed at an angle to the flow of 30° at Re = 4000. The VG installation reduces the recirculation region and the induced longitudinal vortices and rearranges the flow structure in the separation region. The influence of a VG on the local and average thermal characteristics behind the backward-facing step is investigated and their thermohydraulic efficiency is estimated.

Steady longitudinal vortices in supersonic turbulent separated flows

2011 ◽  
Vol 672 ◽  
pp. 451-476 ◽  
Author(s):  
ERICH SCHÜLEIN ◽  
VICTOR M. TROFIMOV
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Roughness Element ◽  
Vortex Generator ◽  
Vortex Pair ◽  
Leading Edge ◽  
Separated Flows ◽  
Vortex Generators ◽  
Longitudinal Vortices ◽  
Oil Flow

Large-scale longitudinal vortices in high-speed turbulent separated flows caused by relatively small irregularities at the model leading edges or at the model surfaces are investigated in this paper. Oil-flow visualization and infrared thermography techniques were applied in the wind tunnel tests at Mach numbers 3 and 5 to investigate the nominally 2-D ramp flow at deflection angles of 20°, 25° and 30°. The surface contour anomalies have been artificially simulated by very thin strips (vortex generators) of different shapes and thicknesses attached to the model surface. It is shown that the introduced streamwise vortical disturbances survive over very large downstream distances of the order of 104 vortex-generator heights in turbulent supersonic flows without pressure gradients. It is demonstrated that each vortex pair induced in the reattachment region of the ramp is definitely a child of a vortex pair, which was generated originally, for instance, by the small roughness element near the leading edge. The dependence of the spacing and intensity of the observed longitudinal vortices on the introduced disturbances (thickness and spanwise size of vortex generators) and on the flow parameters (Reynolds numbers, boundary-layer thickness, compression corner angles, etc.) has been shown experimentally.

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