Measurements of Low Reynolds Number Flow in Rotating Channels

2007 ◽  
Author(s):  
Alberto Di Sante ◽  
Rene´ Van den Braembussche
Keyword(s):  
Reynolds Number ◽  
Turbulence Intensity ◽  
High Speed ◽  
Low Reynolds Number ◽  
Continuous Light ◽  
Suction Side ◽  
Pressure Side ◽  
Low Reynolds ◽  
The Impact ◽  
Rotating Channel

The impact of Coriolis forces on low Reynolds number decelerating flows is studied by means of time resolved Particle Image Velocimetry in a 6° diverging channel. Measurements are made with a high speed camera and a continuous light source rotating at the same speed as the rotating channel. This allows a direct and accurate recording of the time varying relative velocity. The Reynolds number can be varied from 3 000 to 30 000 in combination with a change of rotation number between 0.0 and 0.33. These values are characteristic for the flow in the blade passage of centrifugal impellers used in micro gasturbines. Increasing rotation stabilizes the flow on the suction side. The peak turbulence intensity shifts away from the wall with a small increase of its amplitude. The turbulence intensity on the pressure side increases its peak value and concentrates closer to the wall when increasing rotation. Instantaneous flow field analyses indicate that elongated vortical structures characterize the boundary layer in the stationary case and on the pressure side of the rotating channel. Isotropic vortices develop relatively distant from the wall on the suction side. Their position and size are tracked in time by means of a wavelet analysis.

scholarly journals Aerodynamic characteristics of owl like airfoil at low reynolds number.

2022 ◽  
pp. 26-34
Author(s):  
Ishfaq Fayaz ◽  
Syeeda Needa Fathima ◽  
Y.D. Dwivedi
Keyword(s):  
Reynolds Number ◽  
Separation Bubble ◽  
Low Reynolds Number ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Pressure Side ◽  
Low Reynolds Numbers ◽  
Lift Curve ◽  
Low Reynolds

The computational investigation of aerodynamic characteristics and flow fields of a smooth owl-like airfoil without serrations and velvet structures.The bioinspired airfoil design is planned to serve as the main-wing for low-reynolds number aircrafts such as (MAV)micro air vechiles.The dependency of reynolds number on aerodynamics could be obtained at low reynolds numbers.The result of this experiment shows the owl-like airfoil is having high lift performance at very low speeds and in various wind conditions.One of the unique feature of owl airfoil is a separation bubble on the pressure side at low angle of attack.The separation bubble changes location from the pressure side to suction side as the AOA (angle of attack) increases. The reynolds number dependancy on the lift curve is insignificant,although there’s difference in drag curve at high angle of attacks.Eventually, we get the geometric features of the owl like airfoil to increase aerodynamic performance at low reynolds numbers.

scholarly journals Turbulence Measurements of High Shear Flow Fields in a Turbomachine Seal Configuration

1993 ◽  
Vol 115 (4) ◽  
pp. 670-677 ◽  
Author(s):  
G. L. Morrison ◽  
R. E. DeOtte ◽  
H. D. Thames
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Recirculation Zone ◽  
Low Reynolds Number ◽  
Suction Side ◽  
Pressure Side ◽  
Tangential Momentum ◽  
Low Reynolds ◽  
High Reynolds ◽  
Number Case

The mean velocity and Reynolds stress tensor throughout a whirling annular seal are presented. The data were collected with a three-dimensional laser Doppler velocimeter using phase averaging. Two axial flow conditions (Re = 12,000 and 24,000) were studied at one shaft speed (Ta = 6,600). The eccentricity and whirl ratios were 50 percent and 100 percent, respectively. There is a region of high axial momentum at the inlet on the pressure side of the clearance that migrates around the seal to the suction side at the exit. The normalized axial momentum in this region is higher in the low Reynolds number case due to an axial recirculation zone that occurs on the suction side of the rotor at the inlet. The recirculation zone does not occur in the high Reynolds number case. At both Reynolds numbers there is a recirculation zone on the rotor surface in the pressure side of the inlet. This recirculation zone extends from 20 to 200 deg past the rotor zenith in the tangential direction, and is one third of a clearance wide radially. The high Reynolds number circulation zone is 1.5 mean clearances long, while the low Reynolds number zone extends two mean clearances downstream. When compared to previous studies, it is apparent that the tangential momentum is no greater for a seal with whirl than for one without if other parameters are constant. Areas of high tangential momentum occur in the clearance where the axial momentum is low. Average exit plane tangential velocities in the low Reynolds number case are 1.5 times greater than those in the other flow case. These results are in general agreement with predictions made by other investigators.

Comparative Investigation of Laminar Separation Bubble on a Wing at Low Reynolds Number

2020 ◽  
Vol 12 (3) ◽  
Author(s):  
M.P. Uthra ◽  
A. Daniel Antony
Keyword(s):  
Reynolds Number ◽  
Separation Bubble ◽  
Low Reynolds Number ◽  
Flow Characteristics ◽  
Suction Side ◽  
Aerodynamic Performance ◽  
Laminar Separation Bubble ◽  
Laminar Separation ◽  
Low Reynolds ◽  
Air Vehicles

Most admirable and least known features of low Reynolds number flyers are their aerodynamics. Due to the advancements in low Reynolds number applications such as Micro Air vehicles (MAV), Unmanned Air Vehicles (UAV) and wind turbines, researchers’ concentrates on Low Reynolds number aerodynamics and its effect on aerodynamic performance. The Laminar Separation Bubble (LSB) plays a deteriorating role in affecting the aerodynamic performance of the wings. The parametric study has been performed to analyse the flow around cambered, uncambered wings with different chord and Reynolds number in order to understand the better flow characteristics, LSB and three dimensional flow structures. The computational results are compared with experimental results to show the exact location of LSB. The presence of LSB in all cases is evident and it also affects the aerodynamic characteristics of the wing. There is a strong formation of vortex in the suction side of the wing which impacts the LSB and transition. The vortex structures impact on the LSB is more and it also increases the strength of the LSB throughout the span wise direction.

A CFD Study of Low Reynolds Number Flow in High Lift Cascades

2010 ◽  
Author(s):  
Roberto Pacciani ◽  
Michele Marconcini ◽  
Andrea Arnone ◽  
Francesco Bertini
Keyword(s):  
Reynolds Number ◽  
Separation Bubble ◽  
Structural Characteristics ◽  
Low Reynolds Number ◽  
Separated Flow ◽  
Flow Region ◽  
Suction Side ◽  
Transitional Region ◽  
High Lift ◽  
Low Reynolds

A study of the separated flow in high-lift, low-Reynolds-number cascade, has been carried out using a novel three-equation, transition-sensitive, turbulence model. It is based on the coupling of an additional transport equation for the so-called laminar kinetic energy with the Wilcox k-ω model. Such an approach takes into account the increase of the non-turbulent fluctuations in the pre-transitional and transitional region. Two high-lift cascades (T106C and T108), recently tested at the von Ka´rma´n Institute in the framework of the European project TATMo (Turbulence and Transition Modelling for Special Turbomachinery Applications), were analyzed. The two cascades have different loading distributions and suction side diffusion rates, and therefore also different separation bubble characteristics and loss levels. The analyzed Reynolds number values span the whole range typically encountered in aeroengines low-pressure turbines operations. Several expansion ratios for steady inflow conditions characterized by different freestream turbulence intensities were considered. A detailed comparison between measurements and computations, including bubble structural characteristics, will be presented and discussed. Results with the proposed model show its ability to predict the evolution of the separated flow region, including bubble bursting phenomena, in high-lift cascades operating in LP-turbine conditions.

Approximate Analytical Model for Oil Film Force of Finite Length Squeeze Film Damper Under Low Reynolds Number

2013 ◽  
Author(s):  
Yongliang Wang ◽  
Yu Gao ◽  
Jingjun Zhong ◽  
Ling Yang ◽  
Huawei Lu
Keyword(s):  
Reynolds Number ◽  
Analytical Model ◽  
Finite Length ◽  
High Speed ◽  
Low Reynolds Number ◽  
Separation Of Variables ◽  
Squeeze Film ◽  
Force Model ◽  
Oil Film ◽  
Low Reynolds

Squeeze film dampers (SFDs) are widely used in aero-engines and other high speed rotating machines as damping elements, owing to their remarkable damping effect. The oil-film force model of SFDs is the key to investigate the dynamic characteristics of the rotor-bearing systems involving SFDs. In this paper, the analytical solution of the oil film pressure of a finite length SFD is obtained by employing the separation of variables method to solve the Reynolds equation (at low Reynolds number) based upon the dynamic π boundary condition. The analytical expression of the oil film force is then derived by applying the integral method. The oil film force from the analytical model is compared with the results from other well-known methods, i.e. the long bearing approximation, the short bearing approximation and the finite difference method. The results clearly show that within a wider length-diameter ratio range, the newly proposed model can accurately predict the oil film characteristics of the SFDs at low Reynolds numbers.

Surface Thin Film Gauge Measurements in a Two-Stage Low Pressure Turbine at Low Reynolds Number

2012 ◽  
Author(s):  
Matthias Kürner ◽  
Martin G. Rose ◽  
Stephan Staudacher ◽  
Jochen Gier ◽  
Andreas Fiala ◽  
...  
Keyword(s):  
Thin Film ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Suction Side ◽  
Low Pressure ◽  
Test Facility ◽  
Two Stage ◽  
Low Reynolds ◽  
Aero Engines

A two-stage low pressure axial turbine has been tested in cooperation between the Institute of Aircraft Propulsion Systems (ILA) and MTU Aero Engines GmbH (MTU). The experimental results taken in the Altitude Test Facility are used to assess blade row performance of vane 2 at mid height over a range of Reynolds numbers from as low as 35,000 up to 88,000. Both Mach and Reynolds similarity are preserved. Surface thin film gauges at midspan on vane 2 suction side are used to analyse the unsteady behaviour of the boundary layer. Unsteady data from area traverses downstream of vane 2 using X-hotfilm probes complement the analysis describing the unsteady wake evolution at mid height. The nature of the unsteady transitional low Reynolds number boundary layer is discussed.

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