Unsteady Flow Features of a Flapping and Pitching Wing at Low Reynolds Number

2006 ◽  
Author(s):  
K Isaac ◽  
Jessica Rolwes ◽  
Anthony Colozza
Keyword(s):  
Reynolds Number ◽  
Unsteady Flow ◽  
Low Reynolds Number ◽  
Flow Features ◽  
Low Reynolds

A note on the flow coefficients of capillary tube and small orifice restrictors exposed to very low Reynolds number flow

2005 ◽  
Vol 57 (3) ◽  
pp. 116-120 ◽  
Author(s):  
Suat Canbazoğlu ◽  
Fazıl Canbulut
Keyword(s):  
Reynolds Number ◽  
Unsteady Flow ◽  
Capillary Tube ◽  
Low Reynolds Number ◽  
Reynolds Numbers ◽  
Hydraulic Control ◽  
Capillary Tubes ◽  
Content Type ◽  
Control Devices ◽  
Low Reynolds

PurposeThe main objective of this study was to obtain the flow restricting capacity by determining their flow coefficients and to investigate the unsteady flow with low Reynolds number in the flow‐restricting devices such as orifices and capillary tubes having small diameters.Design/methodology/approachThere is an enormous literature on the flow of Newtonian fluids through capillaries and orifices particularly in many application fields of the mechanical and chemical engineering. But most of the experimental results in literature are given for steady flows at moderate and high Reynolds numbers (Re>500). In this study, the unsteady flow at low Reynolds number (10<Re<650) through flow‐restricting devices such as orifices and capillary tubes having very small diameters between 0.35 and 0.70 mm were experimentally investigated.FindingsThe capillary tubes have much more capillarity property with respect to equal diameter orifices. Increasing the ratio of capillary tube length to tube diameter and decreasing the ratio of orifice diameter to pipe diameter before orifice increase the throttling or restricting property of the orifices and the capillary tubes. The orifices can be preferred to the capillary tubes having the same diameter at the same system pressure for the hydraulic systems or circuits requiring small velocity variations. The capillary tubes provide higher pressure losses and they can be also used as hydraulic accumulators in hydraulic control devices to attenuate flow‐induced vibrations because of their large pressure coefficients. An important feature of the results obtained for capillary tubes and small orifices is that as the d/D for orifices increases and the L/d reduces for capillary tubes, higher values C are obtained and the transition from viscous to inertia‐controlled flow appears to take place at lower Reynolds numbers. This may be explained by the fact that for small orifices with high d/D ratios and for capillary tubes with small L/d ratios, the losses due to viscous shear are small. Another important feature of the results is that the least variations in C for small orifices and the higher variations in C for capillary tubes occur when the d/D and L/d ratios are smallest. This has favourable implications in hydraulic control devices since a constant value for the C may be assumed even at relatively low values of Re.Originality/valueTo the authors' knowledge, there is not enough information in the literature about the flow coefficients of unsteady flows through capillary tubes and small orifices at low Reynolds numbers. This paper fulfils this gap.

Unsteady Flow Field of an Axial-Flow Turbine Rotor at a Low Reynolds Number

2006 ◽  
Author(s):  
Takayuki Matsunuma
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Unsteady Flow ◽  
Low Reynolds Number ◽  
Axial Flow ◽  
Turbine Rotor ◽  
Frame Of Reference ◽  
Flow Angle ◽  
Low Reynolds ◽  
Secondary Vortices

The unsteady flow field of an annular turbine rotor was investigated experimentally using a laser Doppler velocimetry (LDV) system. Detailed measurements of the time-averaged and time-resolved distributions of the velocity, flow angle, and turbulence intensity, etc. were carried out at a very low Reynolds number condition, Reout = 3.5 × 104. The data obtained were analyzed from the viewpoints of both an absolute (stationary) frame of reference and a relative (rotating) frame of reference. The effect of the turbine nozzle wake and secondary vortices on the flow field inside the rotor passage was clearly captured. It was found that the nozzle wake and secondary vortices are suddenly distorted at the rotor inlet, because of the rotating potential field of the rotor. The nozzle flow (wake and passage vortices) and the rotor flow (boundary layer, wake, tip leakage vortex, and passage vortices) interact intensively inside the rotor passage.

Unsteady Flow Separation and High Performance of Airfoil with Local Flexible Structure at Low Reynolds Number

2014 ◽  
Vol 16 (3) ◽  
pp. 699-717 ◽  
Author(s):  
Peng-Fei Lei ◽  
Jia-Zhong Zhang ◽  
Wei Kang ◽  
Sheng Ren ◽  
Le Wang
Keyword(s):  
Reynolds Number ◽  
Unsteady Flow ◽  
Flow Separation ◽  
High Performance ◽  
Energy Transport ◽  
Low Reynolds Number ◽  
Flexible Structure ◽  
Arbitrary Lagrangian Eulerian ◽  
Aeroelastic System ◽  
Low Reynolds

AbstractThe unsteady flow separation of airfoil with a local flexible structure (LFS) is studied numerically in Lagrangian frames in detail, in order to investigate the nature of its high aerodynamic performance. For such aeroelastic system, the characteristic-based split (CBS) scheme combined with arbitrary Lagrangian-Eulerian (ALE) framework is developed firstly for the numerical analysis of unsteady flow, and Galerkin method is used to approach the flexible structure. The local flexible skin of airfoil, which can lead to self-induced oscillations, is considered as unsteady perturbation to the flow. Then, the ensuing high aerodynamic performances and complex unsteady flow separation at low Reynolds number are studied by Lagrangian coherent structures (LCSs). The results show that the LFS has a significant influence on the unsteady flow separation, which is the key point for the lift enhancement. Specifically, the oscillations of the LFS can induce the generations of moving separation and vortex, which can enhance the kinetic energy transport from main flow to the boundary layer. The results could give a deep understand of the dynamics in unsteady flow separation and flow control for the flow over airfoil.

scholarly journals Flow Features of Three Side-by-side Circular Cylinders at Low Reynolds Number

2016 ◽  
Vol 77 ◽  
pp. 04007
Author(s):  
Junkao Liu ◽  
Yaqiang Hao ◽  
Dibo Dong ◽  
Weishan Chen
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Circular Cylinders ◽  
Flow Features ◽  
Low Reynolds

Unsteady Flow Field of an Axial-Flow Turbine Rotor at a Low Reynolds Number

2006 ◽  
Vol 129 (2) ◽  
pp. 360-371 ◽  
Author(s):  
Takayuki Matsunuma
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Unsteady Flow ◽  
Low Reynolds Number ◽  
Axial Flow ◽  
Turbine Rotor ◽  
Frame Of Reference ◽  
Flow Angle ◽  
Low Reynolds ◽  
Secondary Vortices

The unsteady flow field of an annular turbine rotor was investigated experimentally using a laser Doppler velocimetry (LDV) system. Detailed measurements of the time-averaged and time-resolved distributions of the velocity, flow angle, turbulence intensity, etc., were carried out at a very low Reynolds number condition, Reout=3.5×104. The data obtained were analyzed from the viewpoints of both an absolute (stationary) frame of reference and a relative (rotating) frame of reference. The effect of the turbine nozzle wake and secondary vortices on the flow field inside the rotor passage was clearly captured. It was found that the nozzle wake and secondary vortices are suddenly distorted at the rotor inlet, because of the rotating potential field of the rotor. The nozzle flow (wake and passage vortices) and the rotor flow (boundary layer, wake, tip leakage vortex, and passage vortices) interact intensively inside the rotor passage.

scholarly journals Effects of Low Reynolds Number on Wake-Generated Unsteady Flow of an Axial-Flow Turbine Rotor

2005 ◽  
Vol 2005 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Takayuki Matsunuma ◽  
Yasukata Tsutsui
Keyword(s):  
Reynolds Number ◽  
Energy Dissipation ◽  
Flow Field ◽  
Unsteady Flow ◽  
Power Law ◽  
Turbulence Intensity ◽  
Low Reynolds Number ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Low Reynolds

The unsteady flow field downstream of axial-flow turbine rotors at low Reynolds numbers was investigated experimentally using hot-wire probes. Reynolds number, based on rotor exit velocity and rotor chord lengthReout,RT, was varied from3.2×104to12.8×104at intervals of1.0×104by changing the flow velocity of the wind tunnel. The time-averaged and time-dependent distributions of velocity and turbulence intensity were analyzed to determine the effect of Reynolds number. The reduction of Reynolds number had a marked influence on the turbine flow field. The regions of high turbulence intensity due to the wake and the secondary vortices were increased dramatically with the decreasing Reynolds number. The periodic fluctuation of the flow due to rotor-stator interaction also increased with the decreasing Reynolds number. The energy-dissipation thickness of the rotor midspan wake at the low Reynolds numberReout,RT=3.2×104was1.5times larger than that at the high Reynolds numberReout,RT=12.8×104. The curve of the−0.2power of the Reynolds number agreed with the measured energy-dissipation thickness at higher Reynolds numbers. However, the curve of the−0.4power law fitted more closely than the curve of the−0.2power law at lower Reynolds numbers below6.4×104.

Unsteady flow mechanism of the integrated aggressive inter-turbine duct in low Reynolds number condition

2020 ◽  
Vol 234 (9) ◽  
pp. 1507-1517
Author(s):  
Hongrui Liu ◽  
Jun Liu ◽  
Qiang Du ◽  
Guang Liu ◽  
Pei Wang
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Unsteady Flow ◽  
Low Reynolds Number ◽  
Low Pressure ◽  
Tip Clearance ◽  
Surface Boundary ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Low Reynolds

Aggressive inter-turbine duct, which has ultra-high bypass ratio and ultra-short axial length, is widely applied in the modern turbofan engine because it can reduce engine weight and improve low-pressure rotor dynamic characteristics. However, the aggressive inter-turbine duct that has swirling flow, wake, shock, and tip clearance leakage flow of upstream high-pressure turbine, and even has structs in its flow channel, is liable to separate, especially in high-altitude low Reynolds number (Re) condition. In addition, its downstream low-pressure turbine is on the edge of separation too. In this paper, an integrated aggressive inter-turbine duct embedded with wide-chord low-pressure turbine nozzle is adopted to eliminate the aggressive inter-turbine duct's end-wall separation. Since there are many studies on suppressing the blade suction surface's separation by upstream wake, in this study inherent wake is utilized to suppress the boundary layer separation on low-pressure turbine nozzle's suction surface in the integrated aggressive inter-turbine duct. The paper studies the unsteady flow mechanisms of the integrated aggressive inter-turbine duct (especially the separation and transition mechanisms of low-pressure turbine nozzle's suction surface boundary layer) by the computatioinal simulation method.

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