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.

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.

scholarly journals Parametric optimization of a stamped longitudinal vortex generator inside a circular tube of a solar water heater at low Reynolds numbers

2021 ◽  
Vol 3 (8) ◽  
Author(s):  
Felipe A. S. Silva ◽  
Luis Júnior ◽  
José Silva ◽  
Sandilya Kambampati ◽  
Leandro Salviano
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Reynolds Numbers ◽  
Geometric Parameters ◽  
Vortex Generators ◽  
Longitudinal Vortex ◽  
Solar Water Heater ◽  
Water Heater ◽  
Solar Water

AbstractSolar Water Heater (SWH) has low efficiency and the performance of this type of device needs to be improved to provide useful and ecological sources of energy. The passive techniques of augmentation heat transfer are an effective strategy to increase the convective heat transfer coefficient without external equipment. In this way, recent investigations have been done to study the potential applications of different inserts including wire coils, vortex generators, and twisted tapes for several solar thermal applications. However, few researchers have investigated inserts in SWH which is useful in many sectors where the working fluid operates at moderate temperatures. The longitudinal vortex generators (LVG) have been applied to promote heat transfer enhancement with a low/moderate pressure drop penalty. Therefore, the present work investigated optimal geometric parameters of LVG to enhance the heat transfer for a SWH at low Reynolds number and laminar flow, using a 3D periodical numerical simulation based on the Finite Volume Method coupled to the Genetic Algorithm optimization method (NSGA-II). The LVG was stamped over a flat plate inserted inside a smooth tube operating under a typical residential application corresponding to Reynolds numbers of 300, 600, and 900. The geometric parameters of LGV were submitted to the optimization procedure which can find traditional LVG such as rectangular-winglet and delta-winglet or a mix of them. The results showed that the application of LGVs to enhance heat transfer is an effective passive technique. The different optimal shapes of the LVG for all Reynolds numbers evaluated improved more than 50% of heat transfer. The highest augmentation heat transfer of 62% is found for the Reynolds number 900. However, the best thermo-hydraulic efficiency value is found for the Reynolds number of 600 in which the heat transfer intensification represents 55% of the pressure drop penalty.

Effects of Reynolds Number and Freestream Turbulence on Turbine Tip Clearance Flow

2005 ◽  
Vol 128 (1) ◽  
pp. 166-177 ◽  
Author(s):  
Takayuki Matsunuma
Keyword(s):  
Reynolds Number ◽  
Turbulence Intensity ◽  
Three Dimensional ◽  
Tip Clearance ◽  
Pressure Probe ◽  
Turbine Cascade ◽  
Freestream Turbulence ◽  
Tip Leakage Flow ◽  
Three Dimensional Flow ◽  
Dimensional Flow

Tip clearance losses represent a major efficiency penalty of turbine blades. This paper describes the effect of tip clearance on the aerodynamic characteristics of an unshrouded axial-flow turbine cascade under very low Reynolds number conditions. The Reynolds number based on the true chord length and exit velocity of the turbine cascade was varied from 4.4×104 to 26.6×104 by changing the velocity of fluid flow. The freestream turbulence intensity was varied between 0.5% and 4.1% by modifying turbulence generation sheet settings. Three-dimensional flow fields at the exit of the turbine cascade were measured both with and without tip clearance using a five-hole pressure probe. Tip leakage flow generated a large high total pressure loss region. Variations in the Reynolds number and freestream turbulence intensity changed the distributions of three-dimensional flow, but had no effect on the mass-averaged tip clearance loss of the turbine cascade.

Turbulence Measurements in the Corner Wall Jet

2014 ◽  
Author(s):  
Barrett Poole ◽  
Joseph W. Hall
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Turbulent Flow ◽  
Three Dimensional ◽  
Wall Jet ◽  
Hot Wire ◽  
Turbulence Measurements ◽  
Vertical Growth ◽  
The Mean ◽  
Turbulent Flow Field

The corner wall jet is similar to the standard three-dimensional wall jet with the exception that one half of the surface has been rotated counter-clockwise by 90 degrees. The corner wall jet investigated here is formed using a long round pipe with a Reynolds number of 159,000. Contours of the mean and turbulent flow field were measured using hot-wire anemometry. The results indicate that the ratio of lateral to vertical growth in the corner wall jet is approximately half of that in a standard turbulent three-dimensional wall jet.

Effects of Reynolds Number and Free-Stream Turbulence on Turbine Tip Clearance Flow

2005 ◽  
Author(s):  
Takayuki Matsunuma
Keyword(s):  
Reynolds Number ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Three Dimensional ◽  
Tip Clearance ◽  
Turbine Cascade ◽  
Tip Leakage Flow ◽  
Three Dimensional Flow ◽  
Free Stream Turbulence ◽  
Dimensional Flow

Tip clearance losses represent a major efficiency penalty of turbine blades. This paper describes the effect of tip clearance on the aerodynamic characteristics of an unshrouded axial-flow turbine cascade under very low Reynolds number conditions. The Reynolds number based on the true chord length and exit velocity of the turbine cascade was varied from 4.4 × 104 to 26.6 × 104 by changing the velocity of fluid flow. The free-stream turbulence intensity was varied between 0.5% and 4.1% by modifying turbulence generation sheet settings. Three-dimensional flow fields at the exit of the turbine cascade were measured both with and without tip clearance using a five-hole pressure probe. Tip leakage flow generated a large high total pressure loss region. Variations in the Reynolds number and free-stream turbulence intensity changed the distributions of three-dimensional flow, but had no effect on the mass-averaged tip clearance loss of the turbine cascade.

The Aerodynamic Mixing Effect of Discrete Cooling Jets With Mainstream Flow on a Highly Loaded Turbine Blade

1996 ◽  
Vol 118 (3) ◽  
pp. 468-478 ◽  
Author(s):  
G. Wilfert ◽  
L. Fottner
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Suction Side ◽  
Horseshoe Vortex ◽  
Surface Flow ◽  
Experimental Investigations ◽  
Turbine Cascade ◽  
Mixing Processes

For the application of film cooling to turbine blades, experimental investigations were performed on the mixing processes in the near-hole region with a row of holes on the suction suction side of a turbine cascade. Data were obtained using pneumatic probes, pressure tappings, and a three-dimensional subminiature hot-wire probe, as well as surface flow visualization techniques. It was found that at low blowing rates, a cooling jet behaves very much like a normal obstacle and the mixing mainly takes place in the boundary layer. With increasing blowing rates, the jet penetrates deeper into the mainstream. The variation of the turbulence level at the inlet of the turbine cascade and the Reynolds number showed a strong influence on the mixing behavior. The kidney-shaped vortex and as an important achievement the individual horseshoe vortex of each single jet were detected and their exact positions were obtained. This way it was found that the position of the horseshoe vortex is strongly dependent on the blowing rate and this influences the aerodynamic mixing mechanisms. A two-dimensional code for the calculation of boundary layer flows called GRAFTUS was used; however, the comparison with the measurements showed only limited agreement for cascade flow with blowing due to the strong three-dimensional flow pattern.

Effect of Longitudinal Vortex on Boundary Layer State and Separation on NACA Symmetric Foil

2010 ◽  
Author(s):  
Sebastien Prothin ◽  
Henda Djeridi ◽  
Jean-Yves Billard
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Shape Factor ◽  
Base Flow ◽  
Vortex Generators ◽  
Longitudinal Vortex ◽  
Velocity Measurements ◽  
Number Range ◽  
Fluid Displacement ◽  
High Reynolds

Vortex generators have been widely used in aerodynamics to control the separation of boundary layers. In such application (Angele and Muhammad, 2005) vortex generators are embedded in the boundary layer and the vortex height, with regards to the wall, is of the boundary layer thickness. The objective of this configuration is obviously far from being the effects of a single longitudinal vortex (generated upstream by an elliptical plan form profile) on the turbulent boundary layer shape over a Naca0015 symmetric foil at different incidences at high Reynolds number 5 105. The vortex is situated outside the boundary layer (ten times the BL thickness over the wall) taking into account the small value of the thickness in our hydrodynamic application. Obviously, this situation is optimum as the vortex delays separation and increases the maximum lift but introduces drag penalty at small incidence. This is nevertheless frequently encountered in hydrodynamic applications (hub vortex upstream of a rudder) and of interest. To point out the mechanism of the boundary layer manipulation, both global efforts using gauge balance and velocity measurements using LDV and PIV have been performed and compared with and without vortex. The base flow is an APG boundary layer characterized by a predominant wake area. Effect of the vortex is analyzed via the shape factor both in inflow and outflow regions. The longitudinal vortex suppress the hysteretic loop classically described in this Reynolds number range (Djeridi et al., 2009) but an increase of the drag is observed in the range of incidence just before stall. Velocity measurements indicated that, for incidences near the stall appearance, the shape factor is decreased both in the inflow and in the outflow regions. Even for large incidences, in the inflow region the value of the shape factor is equivalent to the one found in the turbulent BL over a flat plate. In this region the vortex modifies the equilibrium state of the BL as attested by the Clauser parameter. Even for large distances between the vortex and the wall, the ability of the vortex to suppress the detachment of the BL is observed on the evolution of the backflow coefficient. This effect is greater pronounced in inflow area near the trailing edge region where the flow is locally reattached due to the high momentum fluid displacement.

The aeroacoustics of finite wall-mounted square cylinders

2017 ◽  
Vol 832 ◽  
pp. 287-328 ◽  
Author(s):  
Ric Porteous ◽  
Danielle J. Moreau ◽  
Con J. Doolan
Keyword(s):  
Boundary Layer ◽  
Experimental Study ◽  
Reynolds Number ◽  
Wind Tunnel ◽  
Three Dimensional ◽  
Flow Structures ◽  
Hot Wire ◽  
Radiated Noise ◽  
Aspect Ratios ◽  
Square Cylinders

This paper presents the results of an experimental study that relates the flow structures in the wake of a square finite wall-mounted cylinder with the radiated noise. Acoustic and hot-wire measurements were taken in an anechoic wind tunnel. The cylinder was immersed in a near-zero-pressure gradient boundary layer whose thickness was 130 % of the cylinder width, $W$. Aspect ratios were in the range $0.29\leqslant L/W\leqslant 22.9$ (where $L$ is the cylinder span), and the Reynolds number, based on width, was $1.4\times 10^{4}$. Four shedding regimes were identified, namely R0 ($L/W<2$), RI ($2<L/W<10$), RII ($10<L/W<18$) and RIII ($L/W>18$), with each shedding regime displaying an additional acoustic tone as the aspect ratio was increased. At low aspect ratios (R0 and RI), downwash dominated the wake, creating a highly three-dimensional shedding environment with maximum downwash at $L/W\approx 7$. Looping vortex structures were visualised using a phase eduction technique. The principal core of the loops generated the most noise perpendicular to the cylinder. For higher aspect ratios in RII and RIII, the main noise producing structures consisted of a series of inclined vortex filaments, where the angle of inclination varied between vortex cells.

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