Comparison of Noise Sources in High and Low Reynolds Number High Speed Jets

2005 ◽  
Author(s):  
Jeff Kastner ◽  
Mo Samimy ◽  
Jim Hileman ◽  
Jon Freund
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Low Reynolds Number ◽  
Noise Sources ◽  
Low Reynolds

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.

Active control of high-speed and high-Reynolds-number jets using plasma actuators

2007 ◽  
Vol 578 ◽  
pp. 305-330 ◽  
Author(s):  
M. SAMIMY ◽  
J.-H. KIM ◽  
J. KASTNER ◽  
I. ADAMOVICH ◽  
Y. UTKIN
Keyword(s):  
Reynolds Number ◽  
Nozzle Exit ◽  
High Speed ◽  
Low Reynolds Number ◽  
Plasma Actuators ◽  
Mixing Enhancement ◽  
Azimuthal Mode ◽  
Potential Core ◽  
Low Speed ◽  
Low Reynolds

Localized arc filament plasma actuators are used to control an axisymmetric Mach 1.3 ideally expanded jet of 2.54 cm exit diameter and a Reynolds number based on the nozzle exit diameter of about 1.1×106. Measurements of growth and decay of perturbations seeded in the flow by the actuators, laser-based planar flow visualizations, and particle imaging velocimetry measurements are used to evaluate the effects of control. Eight actuators distributed azimuthally inside the nozzle, approximately 1 mm upstream of the nozzle exit, are used to force various azimuthal modes over a large frequency range (StDF of 0.13 to 1.3). The jet responded to the forcing over the entire range of frequencies, but the response was optimum (in terms of the development of large coherent structures and mixing enhancement) around the jet preferred Strouhal number of 0.33 (f = 5 kHz), in good agreement with the results in the literature for low-speed and low-Reynolds-number jets. The jet (with a thin boundary layer, D/θ ∼ 250) also responded to forcing with various azimuthal modes (m = 0 to 3 and m = ±1, ±2, ±4), again in agreement with instability analysis and experimental results in the literature for low-speed and low-Reynolds-number jets. Forcing the jet with the azimuthal mode m = ±1 at the jet preferred-mode frequency provided the maximum mixing enhancement, with a significant reduction in the jet potential core length and a significant increase in the jet centreline velocity decay rate beyond the end of the potential core.

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 An assessment of the laminar kinetic energy concept for the prediction of high-lift, low-Reynolds number cascade flows

2011 ◽  
Vol 225 (7) ◽  
pp. 995-1003 ◽  
Author(s):  
R Pacciani ◽  
M Marconcini ◽  
A Arnone ◽  
F Bertini
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
High Speed ◽  
Low Reynolds Number ◽  
Flow Region ◽  
Freestream Turbulence ◽  
High Lift ◽  
Numerical Predictions ◽  
Wide Range ◽  
Low Reynolds

The laminar kinetic energy (LKE) concept has been applied to the prediction of low-Reynolds number flows, characterized by separation-induced transition, in high-lift airfoil cascades for aeronautical low-pressure turbine applications. The LKE transport equation has been coupled with the low-Reynolds number formulation of the Wilcox's k − ω turbulence model. The proposed methodology has been assessed against two high-lift cascade configurations, characterized by different loading distributions and suction-side diffusion rates, and tested over a wide range of Reynolds numbers. The aft-loaded T106C cascade is studied in both high- and low-speed conditions for several expansion ratios and inlet freestream turbulence values. The front-loaded T108 cascade is analysed in high-speed, low-freestream turbulence conditions. Numerical predictions with steady inflow conditions are compared to measurements carried out by the von Kármán Institute and the University of Cambridge. Results obtained with the proposed model show its ability to predict the evolution of the separated flow region, including bubble-bursting phenomenon and the formation of open separations, in high-lift, low-Reynolds number cascade flows.

Combined Aerodynamic and Phased Array Microphone Studies on Basic Models of Low-Speed Axial Fan Blade Sections

2018 ◽  
Author(s):  
Esztella Balla ◽  
János Vad
Keyword(s):  
Reynolds Number ◽  
Phased Array ◽  
High Efficiency ◽  
Low Reynolds Number ◽  
Low Noise ◽  
Axial Fan ◽  
Noise Sources ◽  
Low Speed ◽  
Axial Fans ◽  
Low Reynolds

The paper presents comparative aerodynamic and aeroacoustic studies on basic models of blade sections of low-speed, low-Reynolds-number axial fans. The wind tunnel experiments incorporated representative cambered plate and airfoil blade profiles. The aerodynamic measurements revealed that, for low Reynolds numbers, cambered plate blade sections may perform aerodynamically better than airfoil sections. A phased array microphone system, combined with a dipole beamforming and spatial filtering technique, offered a potential for localizing the noise sources in both streamwise and transversal direction. The acoustic studies focused on the profile vortex shedding noise. The results were qualitatively evaluated and compared with the semi-empirical noise prediction model developed by Brooks, Pope, and Marcolini. The measurements are considered as preparation of a dataset contributing to the background for designing high-efficiency, low-noise axial fans operating at low Reynolds number.

scholarly journals Choreographed swimming of copepod nauplii

2015 ◽  
Vol 12 (112) ◽  
pp. 20150776 ◽  
Author(s):  
Petra H. Lenz ◽  
Daisuke Takagi ◽  
Daniel K. Hartline
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Low Reynolds Number ◽  
Measurement Model ◽  
The Body ◽  
Morphological Data ◽  
Slender Body Theory ◽  
Viscous Forces ◽  
Video Images ◽  
Low Reynolds

Small metazoan paddlers, such as crustacean larvae (nauplii), are abundant, ecologically important and active swimmers, which depend on exploiting viscous forces for locomotion. The physics of micropaddling at low Reynolds number was investigated using a model of swimming based on slender-body theory for Stokes flow. Locomotion of nauplii of the copepod Bestiolina similis was quantified from high-speed video images to obtain precise measurements of appendage movements and the resulting displacement of the body. The kinematic and morphological data served as inputs to the model, which predicted the displacement in good agreement with observations. The results of interest did not depend sensitively on the parameters within the error of measurement. Model tests revealed that the commonly attributed mechanism of ‘feathering’ appendages during return strokes accounts for only part of the displacement. As important for effective paddling at low Reynolds number is the ability to generate a metachronal sequence of power strokes in combination with synchronous return strokes of appendages. The effect of feathering together with a synchronous return stroke is greater than the sum of each factor individually. The model serves as a foundation for future exploration of micropaddlers swimming at intermediate Reynolds number where both viscous and inertial forces are important.

Magnetic Control of Biologically Inspired Robotic Microswimmers

2011 ◽  
Author(s):  
U. Kei Cheang ◽  
Jun Hee Lee ◽  
Paul Kim ◽  
Min Jun Kim
Keyword(s):  
Magnetic Field ◽  
Reynolds Number ◽  
High Speed ◽  
Low Reynolds Number ◽  
Rotating Magnetic Field ◽  
Power Supplies ◽  
Magnetic Control ◽  
Function Generator ◽  
Flagellar Filament ◽  
Low Reynolds

Bacterial flagella have been employed as nanoactuators for biomimetic microswimmers in low Reynolds number fluidic environments. The microswimmer is a dumbbell-like swimmer that utilizes flagellar hydrodynamics to achieve spiral-type swimming. Flagellar filaments from Salmonella typhimurium are harnessed and functionalized in order to serve as couplers for polystyrene (PS) microbeads and magnetic nanoparticles (MNPs) using avidin-biotin chemistry. The MNP have an iron oxide core that will allow us to actuate the microswimmer under a rotating magnetic field. Using a micromanufacturing process, microswimmer of different configurations can be created to mimic mono- and multi-flagellated bacteria. A magnetic control system consists of electromagnetic coils arranged in an approximate Helmholtz configuration was designed, constructed, and characterized. In conjunction with a LabVIEW input interface, a DAQ controller was used as a function generator to generate sinusoidal waveforms to the power supplies. AC current outputs were supplied from the power supplies to the coils in order to generate a rotating magnetic field. A rotating magnetic field will induce rotation in the flagella conjugated MNP which in term will rotate the flagellar filament into a spiral configuration and achieve propulsion, as in polarly-flagellated bacteria. A high-speed camera provided real-time imaging of the microswimmer motion in a static fluidic environment inside a closed PDMS (Polydimethylsiloxane) chamber. The microswimmers exhibited flagellar propulsion in a low Reynolds number fluidic environment under a rotating magnetic field, which demonstrates its potential for biomedical applications.

Comparison of Noise Mechanisms in High and Low Reynolds Number High-Speed Jets

AIAA Journal ◽  
2006 ◽  
Vol 44 (10) ◽  
pp. 2251-2258 ◽  
Author(s):  
J. Kastner ◽  
M. Samimy ◽  
J. Hileman ◽  
J. B. Freund
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Low Reynolds Number ◽  
Low Reynolds

scholarly journals Multirotor Drone Aerodynamic Interaction Investigation

Drones ◽  
2018 ◽  
Vol 2 (4) ◽  
pp. 43 ◽  
Author(s):  
Dhwanil Shukla ◽  
Narayanan Komerath
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Low Reynolds Number ◽  
Performance Measurements ◽  
Factors Affecting ◽  
Wide Range ◽  
Wake Interactions ◽  
Low Reynolds ◽  
And Performance ◽  
Thrust And Torque

Aerodynamic interactions between rotors are important factors affecting the performance of in-plane multirotor Unmanned Air Vehicles (UAVs) or drones, which are the majority of small size UAVs (or mini-drones). Optimal design requires knowledge of the flow features. The low Reynolds number of many UAV rotors raises the question of how these features differ from those expected by traditional analytical methods for rotorcraft. Aerodynamics of a set of side-by-side rotors in hover over a range of rotor separation and Reynolds number is studied using high-speed Stereo Particle Image Velocimetry (SPIV) and performance measurements. The instantaneous and time-averaged SPIV data presented here indicate an increase in inter-rotor wake interactions with decrease in rotor spacing and Reynolds number. A dip in rotor efficiency at small rotor spacing at low Reynolds number is observed through thrust and torque measurements. The basic components of in-plane multirotor wake and velocity profiles are identified and discussed to help generalize the findings to a wide range of drones. However, the data provide confidence in traditional analysis tools, with small modifications.

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