Hydrofoils with Differing Leading-Edge Protuberances: CFD and Experimental Investigations

2021 ◽  
Vol 163 (A3) ◽  
Author(s):  
R Kant ◽  
A Bhattacharyya
Keyword(s):  
Reynolds Number ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Humpback Whales ◽  
Experimental Investigations ◽  
Streamwise Vortices ◽  
Cfd Analyses ◽  
Lift And Drag ◽  
High Angles Of Attack ◽  
Base Design

Leading-edge protuberances on the pectoral fin of humpback whales have been widely adopted to the designs of foils to provide superior lifting characteristics in the post-stall regimes. The present work investigates the lift, drag and flow characteristics of finite-span rectangular hydrofoils having different configurations of two protuberances over the leading edge with NACA 634-021 as the base design section. The results obtained from CFD analyses are validated using lift and drag measurements from experiments. The influence of using a transition-sensitive turbulence model on the results is investigated. It is observed that, in general, a foil with smaller separation between protuberances has better post-stall lift characteristics whereas that with protuberances at larger separation have better pre-stall characteristics. Depending on the separation between them, streamwise vortices are generated from the leading-edge protuberances. The two protuberances can restrict the zone of separation between them at high angles of attack. The influence of Reynolds number on the lifting performance is also investigated.

scholarly journals A large-eddy simulation on a deep-stalled aerofoil with a wavy leading edge

2017 ◽  
Vol 813 ◽  
pp. 23-52 ◽  
Author(s):  
Rafael Pérez-Torró ◽  
Jae Wook Kim
Keyword(s):  
Vortex Shedding ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Domain Size ◽  
Aerodynamic Characteristics ◽  
Streamwise Vortices ◽  
Aerodynamic Forces ◽  
Laminar Separation ◽  
Eddy Simulation ◽  
Large Eddy

A numerical investigation on the stalled flow characteristics of a NACA0021 aerofoil with a sinusoidal wavy leading edge (WLE) at chord-based Reynolds number $Re_{\infty }=1.2\times 10^{5}$ and angle of attack $\unicode[STIX]{x1D6FC}=20^{\circ }$ is presented in this paper. It is observed that laminar separation bubbles (LSBs) form at the trough areas of the WLE in a collocated fashion rather than uniformly/periodically distributed over the span. It is found that the distribution of LSBs and their influence on the aerodynamic forces is strongly dependent on the spanwise domain size of the simulation, i.e. the wavenumber of the WLE used. The creation of a pair of counter-rotating streamwise vortices from the WLE and their evolution as an interface/buffer between the LSBs and the adjacent fully separated shear layers are discussed in detail. The current simulation results confirm that an increased lift and a decreased drag are achieved by using the WLEs compared to the straight leading edge (SLE) case, as observed in previous experiments. Additionally, the WLE cases exhibit a significantly reduced level of unsteady fluctuations in aerodynamic forces at the frequency of periodic vortex shedding. The beneficial aerodynamic characteristics of the WLE cases are attributed to the following three major events observed in the current simulations: (i) the appearance of a large low-pressure zone near the leading edge created by the LSBs; (ii) the reattachment of flow behind the LSBs resulting in a decreased volume of the rear wake; and, (iii) the deterioration of von-Kármán (periodic) vortex shedding due to the breakdown of spanwise coherent structures.

Fluid Flow Characteristics of a Confined Slot Jet Without or With a Target Surface

2005 ◽  
Author(s):  
L. K. Liu ◽  
C. J. Fang ◽  
M. C. Wu ◽  
C. Y. Lee ◽  
Y. H. Hung
Keyword(s):  
Reynolds Number ◽  
Fluid Flow ◽  
Fluid Velocity ◽  
Flow Characteristics ◽  
Target Surface ◽  
Streamwise Velocity ◽  
Separation Distance ◽  
Experimental Investigations ◽  
Flow Parameters ◽  
Fluid Flow Characteristics

A series of experimental investigations with a stringent measurement method on the fluid flow characteristics of slot jet without or with a target surface have been successfully conducted. From all the fluid velocity data measured in the present study, the experimental conditions have been verified to be spanwise-symmetrically maintained and the results have been achieved in a spanwise-symmetric form. Three types of jet configuration without or with target surface are investigated: (A) Confined Slot Jet without Target Surfaces – the fluid flow parameters studied in the present investigation is the jet Reynolds number (ReD). Its ranges are ReD=506-1517. (B) Confined Slot Jet with Smooth Surfaces – the fluid flow parameters studied in the present investigation include the ratio of jet separation distance (H) to nozzle width (W) and the jet Reynolds number (ReD). The ranges of the relevant parameters are H/W=2–10 and ReD=504–1526. (C) Confined Slot Jet with Extended Surfaces – the fluid flow parameters studied include the ratio of jet separation distance (H) to nozzle width (W), the Reynolds number (ReD) and the ratio of extended surface height (Hes) to nozzle width (W). Their ranges are H/W=3–10, Hes/W=0.74-3.40 and ReD=501–1547. The flow characteristics such as the local mean streamwise velocity distribution, mean streamwise velocity decay along jet centerline, local jet turbulence intensity distribution, and turbulence intensities along jet centerline have been presented and discussed in the study.

Investigation of Leading Edge Tubercles with Different Wavelengths in an Annular Compressor Cascade

2018 ◽  
Vol 0 (0) ◽  
Author(s):  
Tan Zheng ◽  
Xiaoqing Qiang ◽  
Jinfang Teng ◽  
Jinzhang Feng
Keyword(s):  
Leading Edge ◽  
Humpback Whales ◽  
Wave Number ◽  
Loss Reduction ◽  
Streamwise Vortices ◽  
Compressor Cascade ◽  
Corner Separation ◽  
Stall Angle ◽  
Geometry Parameter ◽  
And Behavior

Abstract Humpback whales possess bumpy tubercles on the leading edge of their flippers. Due to these leading edge tubercles, whales are able to produce high degree of maneuverability. Inspired by the flippers, this paper applies sinusoidal-like tubercles to the leading edge of blades in an annular compressor cascade, and presents a numerical investigation to explore the effects of tubercles with the aim of controlling the corner separation and reducing losses. Steady 3D RANS simulations are performed to investigate the aerodynamic performance and behavior of the corner separation in compressor cascades with and without leading edge tubercles. A crucial geometry parameter of the tubercles, wavelength, is varied to obtain different configurations. Results show that a smaller wavelength (more wave number) corresponds to a larger loss reduction and the maximum loss reduction reaches to 46.0%. Also, it is found that leading edge tubercles result in a stall delay and the maximum stall angle improvement reaches to 28.1%. Flow visualizations show that leading edge tubercles could induce the formation of counter-rotating streamwise vortices. The interaction between the streamwise vortices and corner separation is thought to be the primary flow mechanism generated by leading edge tubercles in an annular compressor cascade.

Analysis of the Flow Characteristics of Two Nonrotating Rotor Blades

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
R. P. J. O. M. van Rooij
Keyword(s):  
Aspect Ratio ◽  
Dominant Role ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Rotor Blades ◽  
Drag Coefficients ◽  
Wing Model ◽  
Stall Angle ◽  
Twisted Blade ◽  
Lift And Drag

The investigation focuses on the analysis of the airfoil segment performances along rotor blades in the parked configuration. In this research, wind tunnel experiments on two twisted blade geometries with different airfoils played a dominant role. These measurements were carried out by the Swedish Aeronautical Research Institute, former FFA, and by the American National Renewable Energy Laboratories (NREL) during the Unsteady Aerodynamic Experiment. The spans of the blades were 2.375m and 5m, the STORK 5 WPX and the NREL Phase VI blade, respectively. Five span locations (inboard, midspan, outboard, and tip regions) were considered and compared with the 2D airfoil characteristics. Wing model experiments with similar blade aspect ratio were included in the research. Furthermore, the commercial computational fluid dynamics code FLUENT was used for the validation and analysis of the spanwise lift and drag coefficients at four different pitch settings, 20deg, 30deg, 45deg, and 60deg. The computed pressure distributions compared reasonably well, but the derived lift and drag showed quite some differences with the blade measurements. The lift coefficients for the sections beyond the leading-edge stall angle of the STORK blade were larger than for the NREL blade and were close to that of a wing model with similar airfoil and aspect ratio. Lift and drag coefficients for the sections of the two blades were always much smaller than the 2D results. The drag values for both blades showed quite some agreement, and airfoil and blade dependency seemed to be small.

Experimental investigations of pressure loss and heat transfer in a 180° bend of a ribbed two-pass internal cooling channel with engine-similar cross-sections

2009 ◽  
Vol 223 (6) ◽  
pp. 709-719 ◽  
Author(s):  
M Schüler ◽  
S O Neumann ◽  
B Weigand
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Sections ◽  
Pressure Loss ◽  
Leading Edge ◽  
Experimental Investigations ◽  
Strong Increase ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Transfer Enhancement

In the present study, the pressure loss and heat transfer of a two-pass internal cooling channel with engine-similar cross-sections were investigated experimentally. This channel consisted of a trapezoidal leading edge pass, a sharp 180° bend, and a nearly rectangular outlet pass. The investigations focused on the influence of tip-to-web distance and rib configuration on pressure loss and heat transfer. The channel was equipped with skewed ribs (α=45°, P/ e=10, e/ dh=0.1) in an inline and a staggered configuration. The dimensionless tip-to-web distance Wel/ dS was varied from 0.6 to 1.2. The investigated Reynolds number ranged from 15 000 up to 100 000. The experimental results showed a strong increase in pressure loss with decreasing tip-to-web distance, while heat transfer was only slightly increasing. Both rib configurations showed nearly the same heat transfer enhancement in the bend region.

scholarly journals CFD Simulation of Flow Characteristics on Semi-Submersible Platforms

2020 ◽  
Vol 9 (1) ◽  
pp. 2777-2782
Keyword(s):  
Reynolds Number ◽  
Flow Separation ◽  
Cfd Simulation ◽  
Transient Flow ◽  
Flow Characteristics ◽  
Slip Boundary Condition ◽  
Computational Domain ◽  
Hexahedral Mesh ◽  
Four Square ◽  
Lift And Drag

In this paper we present the turbulent flow around a semi-submersible platform, modelled using Ansys Fluent. The computational domain is designed as a rectangular horizontal channel with the semi-submersible platform mounted inside the channel. The top, bottom, left and right walls of the channel are treated with no slip boundary condition. The front and back walls are specified with velocity inlet and pressure outlet boundary conditions. The semi-submersible platform is designed with of two pontoons, four square columns and two bracings. The problem is modelled as three dimensional, transient, incompressible flow and turbulence is modelled using Large eddy simulation (LES) turbulence model. The computational domain is meshed to 4,72,749 hexahedral mesh cells. Parametric study is performed by varying the Reynolds number (Re) in the range of 104 ≤ Re ≤ 106 and also the shape of the columns. The investigation is carried out by plotting stream function, velocity and pressure contours. We observe vortex shedding and flow separation between the front and back columns of the semi-submersible platform. As we increase the Reynolds number the intensity of flow separation also increases. The transient flow characteristics of the lift and drag forces are evaluated by plotting the coefficients of lift and drag for different Reynolds number and column shapes

Flow Characteristics Within and Downstream of a Double-Row Array of Shallow Spherical and Cylindrical Dimples

2006 ◽  
Author(s):  
Artem Khalatov ◽  
Aaron Byerley
Keyword(s):  
Reynolds Number ◽  
Unsteady Flow ◽  
Flow Structure ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Bulk Flow ◽  
Experimental Program ◽  
Double Row ◽  
Motion Feature ◽  
Flow Fluctuations

The experimental program was performed in the U.S. Air Force Academy water tunnel to visualize details of the unsteady flow structure in front of, within and downstream of a double-row array of shallow (h/D = 0.1) spherical and cylindrical dimples placed on a flat plate. The dimple projected diameter was 50.8 mm. The center of the first array was located at 88,0 mm downstream of the elliptically-shaped leading edge of the plate, the spanwise dimple pitch is 76.2 mm (Sz/D = 1.50). The second array was arranged in a staggered mode with the same spanwise pitch and the axial pitch between rows of 88.0 mm (Sx/D = 1.73). The diameter-based Reynolds number ReD ranged from 3,260 to 23,450, while the length-based Reynolds number Rex in front of the first array varied from 4,010 to 28,840. The laminar flow existed upstream of the first array for all flow conditions studied. In front of the second array the flow structure appeared to have either laminar or turbulent depending on the Reynolds number and streamline location. Flow visualizations were performed at 13 different flow speeds using the dye visualization technique. All recordings were made with a SONY-DCR VX2000 video camera. Adobe Premiere 6.5 software was used to analyze the flow characteristics using the slow motion feature. The results presented include details of the unsteady flow structure, bulk flow fluctuations and laminar-turbulent flow transition. The upstream vortex structures reduce bulk flow fluctuations beyond the second array making them smaller than those after the first array. At ReD > 13,000 the spherical dimples in the second array produce more significant bulk flow fluctuations than cylindrical dimples.

Tuft Flow Visualisation on UTM-LST VFE-2 Delta Wing Model Configuration at High Angle of Attacks

2020 ◽  
Vol 17 (3) ◽  
pp. 8214-8223
Author(s):  
M. Said ◽  
M. Imai ◽  
S. Mat ◽  
M. N. Dahalan ◽  
S. Mansor ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Surface Pressure ◽  
Delta Wing ◽  
Measurement Techniques ◽  
Initial Point ◽  
Leading Edge ◽  
Flow Visualisation ◽  
Pressure Measurements ◽  
Wing Model ◽  
High Angles Of Attack

This paper reports on flow visualisation and surface pressure measurements over the upper surface of a blunt-edged delta wing model at high angles of attack. The flow structure above the upper surface of the blunt-edged delta wing was found to be different compared to delta wing with sharp leading edge. The flow becomes more complicated especially in the leading edge region of the wing. Currently, there is no data available to verify if the primary vortex could reach the apex of the wing when the angle of attack is further increased. Most prior experiments were performed at the angles of attack, α, below 23° with only a few experiments that had gone to α = 27°. These prior experiments and some CFD works stipulated that the attached flow continue to exist in the apex region of the delta wing even at very high angles of attack above 23°. In order to verify this hypothesis, several experiments at high angles of attack were conducted in Universiti Teknologi Malaysia Low Speed wind Tunnel (UTM–LST), using a specially constructed VFE2 wing model equipped with blunt leading edges. This series of experiments employed two measurement techniques; the first was the long tuft flow visualisation method, followed by surface pressure measurements. The experiments were performed at Reynolds numbers of 1.0×106 and 1.5×106.  During these experiments, several interesting flow characteristics were observed at high angles of attack, mainly that the flow became more sensitive to changes in Reynolds number and the angles of attack of the wing. When the Reynolds number increased from 1×106 to 1.5×106, the upstream progression of the initial point of the main vortex was relatively delayed compared to the sharp-edged delta wing. The experiments also showed that the flow continued to be attached in the apex region up to α = 27º.

Numerical and Experimental Investigations on a Bio-Inspired Design of Darrieus Vertical Axis Wind Turbine Blades With Leading Edge Tubercles

2022 ◽  
pp. 211-224
Author(s):  
Nishant Mishra ◽  
Punit Prakash ◽  
Anand Sagar Gupta ◽  
Jishnav Dawar ◽  
Alok Kumar ◽  
...  
Keyword(s):  
Turbine Blades ◽  
Leading Edge ◽  
Vertical Axis ◽  
Aerodynamic Performance ◽  
Humpback Whales ◽  
Experimental Investigations ◽  
Vertical Axis Wind Turbine ◽  
Wind Turbine Blades ◽  
Vertical Axis Wind Turbines ◽  
Sst Turbulence Model

Various improvements can be made to Darrieus vertical axis wind turbines (VAWT) for maximum performance in an urban environment. One such improvement is the inclusion of bio-inspired leading-edge tubercles to increase the aerodynamic performance. These structures, found on the flippers of humpback whales, are believed to aid the mammal in quick maneuvering. The objective of the chapter is to investigate and compare the performance of a Darrieus type VAWT with the inclusion of leading edge tubercles. The performance of the turbine with leading-edge tubercles on the blades is compared with the turbine with normal blade, computationally (with computational fluid dynamics using transition SST turbulence model) and experimentally. The focus lies on building an experimental setup to compare the performance of leading-edge tubercles with the baseline turbine.

Sign in / Sign up

Export Citation Format

Share Document