An Experimental Study on Flow Past an Equilateral Triangular Prism at Intermediate Reynolds Number and the Effect of its Orientation

2013 ◽  
Author(s):  
Namit Agrawal ◽  
Sushanta Dutta ◽  
B. K. Gandhi
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Flat Plate ◽  
Shear Layers ◽  
Apex Angle ◽  
Triangular Prism ◽  
Wake Region ◽  
Near Wake ◽  
Intermediate Regime ◽  
Free Shear Layers

This paper explores the effect of two orientations (0° and 180°) on near wake region of an equilateral triangular prism at intermediate Reynolds number. The paper also investigates the effect of Reynolds number on the near wake region at intermediate regime. Two orientations are defined such that the apex of the equilateral triangle is pointing upstream and downstream respectively. The flow field behind a triangular prism is different in these two orientations. When apex angle points upstream it corresponds to a fore-body attached to a flat plate while when apex angle points downstream the flat face acts like a flat plate with an after body attached to it. This after-body penetrates the recirculation zone formed behind the flat plate. These two effects are investigated for various Reynolds numbers in intermediate regime. Factors affecting drag coefficient and Strouhal number are different in both cases. In first case the fore-body changes the flow before it gets separated in two free shear layers. In other words, the fore-body affects the free shear layers formed and hence the drag. In the second case, the two shear layers are formed first then their interaction is modified by the after-body in the near wake region behind the prism. Particle Image Velocimetry (PIV) and Hotwire anemometry is being used in present study. Detailed flow field is investigated in terms of velocity magnitude, stream traces, vorticity contours, centerline recovery, power spectra, velocity profiles, Strouhal number and drag coefficient.

scholarly journals Near-Wake Flow Structure of a Suspended Cylindrical Canopy Patch

Water ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 84 ◽  
Author(s):  
Ayşe Yüksel Ozan ◽  
Didem Yılmazer
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
Green Infrastructure ◽  
Nutrient Management ◽  
Wake Flow ◽  
Wake Region ◽  
Near Wake ◽  
Vegetation Patch ◽  
Comprehensive Picture ◽  
Flowing Waters

Urban stormwater is an important environmental problem, especially for metropolitans worldwide. The most important issue behind this problem is the need to find green infrastructure solutions, which provide water treatment and retention. Floating treatment wetlands, which are porous patches that continue down from the free-surface with a gap between the patch and bed, are innovative instruments for nutrient management in lakes, ponds, and slow-flowing waters. Suspended cylindrical vegetation patches in open channels affect the flow dramatically, which causes a deviation from the logarithmic law. This study considered the velocity measurements along the flow depth, at the axis of the patch, and at the near-wake region of the canopy, for different submerged ratios with different patch porosities. The results of this experimental study provide a comprehensive picture of the effects of different submergence ratios and different porosities on the flow field at the near-wake region of the suspended vegetation patch. The flow field was described with velocity and turbulence distributions along the axis of the patch, both upstream and downstream of the vegetation patch. Mainly, it was found that suspended porous canopy patches with a certain range of densities (SVF20 and SVF36 corresponded to a high density of patches in this study) have considerable impacts on the flow structure, and to a lesser extent, individual patch elements also have a crucial role.

Effect of Freestream Turbulence and Flow Recovery in the Wake of a Flat Plate

2002 ◽  
Author(s):  
F. N. Krampa-Morlu ◽  
R. Balachandar
Keyword(s):  
Flat Plate ◽  
Turbulence Intensity ◽  
Flow Direction ◽  
Wake Region ◽  
Freestream Turbulence ◽  
Near Wake ◽  
Mean Velocity ◽  
Channel Boundary ◽  
The Mean ◽  
Velocity Turbulence

The study of the recovery of an open channel boundary flow in the presence of increased freestream turbulence (FST) generated in the wake region of a surface mounted flat plate is presented. Detailed LDA velocity measurements were obtained upstream and downstream of the flat plate, which is 3 mm in thickness and has a thickness-to-chord ratio of 0.12. The chord is placed parallel to the flow direction. The characteristics of the mean velocity, turbulence intensity, and the velocity skewness and flatness factors were investigated. The skin friction was increased while the strength of the boundary layer wake parameter decreased in the wake region. The turbulence intensity profiles in the wake region increasingly deviated significantly from the upstream profile. Generally, the increased FST noticed in the near-wake region was observed to decay with downstream distance. As a result, the mean velocity and turbulence intensity profiles showed a general sense of recovery towards the state of the approaching flow.

scholarly journals Numerical Investigation on the Effects of Vortex Shedding on Boundary Layer Unsteadiness

1970 ◽  
Vol 37 ◽  
pp. 33-39
Author(s):  
ABM Toufique Hasan ◽  
Dipak Kanti Das
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Finite Element ◽  
Flow Field ◽  
Flat Plate ◽  
Vortex Shedding ◽  
Stokes Equations ◽  
Number Range ◽  
Rotating Speed ◽  
Rotating Circular Cylinder

The interaction between an initially laminar boundary layer developed spatially on a flat plate under the influence of vortex shedding induced from a rotating circular cylinder has been simulated numerically. The rotational speed of the cylinder is varied to generate the vortex shedding of different intensities. Also the flat plate is kept at different positions from the cylinder. Due to asymmetry in the flow field, the present problem is governed by unsteady Navier-Stokes equations which are simulated numerically by finite element method. Computations are carried out for low Reynolds number range up to 1000. Instantaneous development of the flow field, unsteady boundary layer integral parameters, and wall skin friction are presented on different streamwise locations over the plate. From the computation, it is observed that the vortex shedding substantially affects the boundary layer development. The disturbed displacement and momentum thicknesses of the plate increase up to 1.6 times and 2.6 times of the undisturbed flow, respectively. Also the plate shape factor approaches a value of 1.5 which is typical for turbulent flow. This interaction strongly depends on the rotating speed of the cylinder, the relative positions of the cylinder and the plate and also on Reynolds number of the flow. Keywords: Vortex shedding, finite element, boundary layer, wall skin friction.doi:10.3329/jme.v37i0.817Journal of Mechanical Engineering Vol.37 June 2007, pp.33-39

Velocity Measurements Around Film Cooling Holes With Deposition

2010 ◽  
Author(s):  
Kristian Haase ◽  
Jeffrey P. Bons
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Flat Plate ◽  
Film Cooling ◽  
Free Stream ◽  
Density Ratio ◽  
Leading Edge ◽  
Flow Structures ◽  
Particle Image Velocimetry Technique ◽  
Film Cooling Holes

The choice of synthetic fuels (synfuels) in order to achieve greater fuel flexibility may lead to unwanted solid depositions on the blades of turbomachines. The objective of this paper is to gain information of the flow field over a turbine blade with depositions around the film cooling holes. For the investigation the particle image velocimetry technique (PIV) is utilized. The experiments are conducted in a low speed wind tunnel at a Reynolds number of 300,000 based on the distance from the leading edge to the middle of the cooling holes and a Reynolds number of 9,200 based on the hole diameter. Three different simulation plates are tested in the tunnel—a flat plate for comparison, a plate with large depositions only upstream of the holes, and one with smaller depositions all around the holes. The two deposition configurations are scaled models of actual depositions formed at simulated engine flow conditions on a turbine test coupon. The experiments are conducted at four different coolant to free stream blowing ratios—0, 0.5, 1, and 2—and at a density ratio of 1.1. PIV images are taken in four planes from the side of the tunnel to record the main flow structures and in five planes from the end of the tunnel to record the secondary flow structures. The results show that the type of deposition has a large influence on the flow field. With the smaller depositions the penetration of the coolant jet into the free stream is significantly reduced but the dimension and strength of the kidney vortices is increased compared to the flat plate. With the large depositions, on the other hand, the penetration of the coolant jet is much higher due to the ramp effect and the dimension of the secondary vortices is also increased. It can also be seen that the coolant gathers and stays behind the large depositions and then flows off very slowly. Film effectiveness and surface heat flux data acquired with the same plates (and reported previously) allow the identification of flow features and their direct influence on the film cooling performance.

scholarly journals Hyperbolicity, shadowing directions and sensitivity analysis of a turbulent three-dimensional flow

2019 ◽  
Vol 863 ◽  
pp. 644-669 ◽  
Author(s):  
Angxiu Ni
Keyword(s):  
Reynolds Number ◽  
Large Fraction ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Wake Region ◽  
Near Wake ◽  
Three Dimensional Flow ◽  
Long Time ◽  
Cylinder Flow ◽  
Far Wake

This paper uses compressible flow simulation to analyse the hyperbolicity, shadowing directions and sensitivities of a weakly turbulent three-dimensional cylinder flow at Reynolds number 525 and Mach number 0.1. By computing the first 40 covariant Lyapunov vectors (CLVs), we find that unstable CLVs are active in the near-wake region, whereas stable CLVs are active in the far-wake region. This phenomenon is related to hyperbolicity since it shows that CLVs point to different directions; it also suggests that for open flows there is a large fraction of CLVs that are stable. However, due to the extra neutral CLV and the occasional tangencies between CLVs, our system is not uniform hyperbolic. By the non-intrusive least-squares shadowing (NILSS) algorithm, we compute shadowing directions and sensitivities of long-time-averaged objectives. Our results suggest that shadowing methods may be valid for general chaotic fluid problems.

Sign in / Sign up

Export Citation Format

Share Document