Experimental Research on Transition and Flow Separation of Laminar Airfoil

2011 ◽  
Vol 301-303 ◽  
pp. 937-942
Author(s):  
Yu Qin Jiao ◽  
Yan Lu ◽  
Chun Sheng Xiao
Keyword(s):  
Laminar Flow ◽  
Turbulent Flow ◽  
Experimental Research ◽  
Flow Separation ◽  
Flow Speed ◽  
Attack Angle ◽  
Experimental Results ◽  
Experimental Device ◽  
Flow Transition

Experimental research on transition and flow separation of laminar airfoil and the influence of transition and flow separation on the performance of laminar airfoil are carried through. The experimental device and instruments used in the research are introduced. It is shown from the experimental results that at certain scope of attack angle, flow transition shifts from 50%c to 30%c on the upper surface of airfoil model along with 1 degree increase of airfoil attack angle; For flow speed of 35m/s and 50m/s with attack angle from 4 degree to 8 degree, flow separation position don’t vary but only separation scope increase; For flow speed of 15m/s laminar flow separation on the upper surface of airfoil take place at attack angle of 4 degree, flow become attaching at attack angle of 6 degree and turbulent flow separation take place at attack angle of 8 degree.

scholarly journals Contactless Localization of Premature Laminar–Turbulent Flow Transitions on Wind Turbine Rotor Blades in Operation

2020 ◽  
Vol 10 (18) ◽  
pp. 6552
Author(s):  
Daniel Gleichauf ◽  
Michael Sorg ◽  
Andreas Fischer
Keyword(s):  
Image Processing ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
State Of The Art ◽  
Flow Transition ◽  
Transition Line ◽  
Systematic Deviation ◽  
Transition Position ◽  
Layer Flow ◽  
Flow Transitions

Thermographic flow visualization enables a noninvasive detection of the laminar–turbulent flow transition and allows a measurement of the impact of surface erosion and contamination due to insects, rain, dust, or hail by quantifying the amount of laminar flow reduction. The state-of-the-art image processing is designed to localize the natural flow transition as occurring on an undisturbed blade surface by use of a one-dimensional gradient evaluation. However, the occurrence of premature flow transitions leads to a high measurement uncertainty of the localized transition line or to a completely missed flow transition detection. For this reason, regions with turbulent flow are incorrectly assigned to the laminar flow region, which leads to a systematic deviation in the subsequent quantification of the spatial distribution of the boundary layer flow regimes. Therefore, a novel image processing method for the localization of the laminar–turbulent flow transition is introduced, which provides a reduced measurement uncertainty for sections with premature flow transitions. By the use of a two-dimensional image evaluation, local maximal temperature gradients are identified in order to locate the flow transition with a reduced uncertainty compared to the state-of-the-art method. The transition position can be used to quantify the reduction of the laminar flow regime surface area due to occurrences of premature flow transitions in order to measure the influence of surface contamination on the boundary layer flow. The image processing is applied to the thermographic measurement on a wind turbine of the type GE 1.5 sl in operation. In 11 blade segments with occurring premature flow transitions and a high enough contrast of the developed turbulence wedge, the introduced evaluation was able to locate the flow transition line correctly. The laminar flow reduction based on the evaluated flow transition position located with a significantly reduced systematic deviation amounts to 22% for the given measurement and can be used to estimate the reduction of the aerodynamic lift. Therefore, the image processing method introduced allows a more accurate estimation of the effects of real environmental conditions on the efficiency of wind turbines in operation.

Numerical and Experimental Investigation of Low Reynolds Number Effects on Laminar Flow Separation and Transition in a Cascade of Compressor Blades

2000 ◽  
Author(s):  
Shunji Enomoto ◽  
C. Hah ◽  
G. V. Hobson
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Flow Separation ◽  
Low Reynolds Number ◽  
Numerical Procedure ◽  
Compressor Blade ◽  
Navier Stokes ◽  
Flow Transition ◽  
Reynolds Number Effects ◽  
Low Reynolds

The results of an experimental and numerical comparison of the effects of low Reynolds number on flow separation and transition in a controlled-diffusion compressor cascade are presented. The flow separation and subsequent flow transition are associated with low Reynolds number effects in the compressor blade rows. Current steady-state Reynolds-averaged Navier-Stokes codes with available turbulence and transition models do not calculate the current flow phenomena properly. An unsteady three-dimensional Navier-Stokes calculation that applies a third-order accurate upwind method has been performed and the numerical results are compared to the measurements in detail. The results from the current numerical procedure agree very well with the measurements in terms of laminar flow separation, reattachment, and subsequent flow transition at low Reynolds numbers. The present study indicates that flow separation and flow transition inside compressor blade rows at low Reynolds number are phenomena dominated by relatively larger eddies near the wall and can be simulated with the current type of unsteady numerical procedure.

Single-Phase Heat Transfer and Fluid Flow in Micropipes

2003 ◽  
Author(s):  
Gian Piero Celata
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Number ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Transfer Rate ◽  
Single Phase ◽  
Flow Transition ◽  
Laminar And Turbulent Regimes ◽  
Good Agreement

The objective of the present paper is to provide a general overview of the research carried out so far in single-phase heat transfer and flow in capillary (micro) pipes. Laminar flow and laminar-to-turbulent flow transition are analyzed in detail in order to clarify the discrepancies among the results obtained by different researchers. Experiments performed in the ENEA laboratory indicate that in laminar flow regime the friction factor is in good agreement with the Hagen-Poiseuille theory for Reynolds number below 600–800. For higher values of Reynolds number, experimental data depart from the Hagen-Poiseuille law to the side of higher f values. The transition from laminar-to-turbulent flow occurs for Reynolds number in the range 1800–2500. Heat transfer experiments show that heat transfer correlations in laminar and turbulent regimes, developed for conventional (macro) tubes, are not properly adequate for heat transfer rate prediction in microtubes.

Interfacial mass transfer in turbulent flow accompanied by irreversible first order chemical reaction

1979 ◽  
Vol 44 (5) ◽  
pp. 1388-1396
Author(s):  
Václav Kolář ◽  
Zdeněk Brož
Keyword(s):  
Mass Transfer ◽  
Turbulent Flow ◽  
Chemical Reaction ◽  
Experimental Results ◽  
Theoretical Concepts ◽  
First Order ◽  
Order Chemical Reaction ◽  
Interfacial Mass Transfer ◽  
First Order Chemical Reaction

Relations describing the mass transfer accompanied by an irreversible first order chemical reaction are derived, based on the formerly published general theoretical concepts of interfacial mass transfer. These relations are compared with experimental results taken from literature.

The Growth of a Vortex in Turbulent Flow

1965 ◽  
Vol 16 (3) ◽  
pp. 302-306 ◽  
Author(s):  
H. B. Squire
Keyword(s):  
Laminar Flow ◽  
Turbulent Flow ◽  
Eddy Viscosity ◽  
Line Vortex ◽  
Trailing Vortices

SummaryThe growth of a line vortex with time and the spread of a trailing vortex behind a wing due to turbulence are considered. It is shown that the eddy viscosity for this type of motion may be taken to be proportional to the circulation round the vortex and the solution is then similar to the solution for the growth of a vortex in laminar flow. The method is applied to calculate the distance behind a wing for which the trailing vortices will touch one another.

Experimental Research to Evaluate Thermal Behavior of a Brushless Driving Servomotor for Linear Motion NC Axis Experimental Stand

2015 ◽  
Vol 762 ◽  
pp. 55-60
Author(s):  
Georgia Cezara Avram ◽  
Florin Adrian Nicolescu ◽  
Radu Constantin Parpală ◽  
Constantin Dumitrascu
Keyword(s):  
Thermal Behavior ◽  
Mathematical Models ◽  
Experimental Research ◽  
Infrared Imaging ◽  
Experimental Results ◽  
Ball Screw ◽  
Linear Motion ◽  
Functional Optimization ◽  
Thermal Infrared Imaging ◽  
Experimental Stand

This paper presents the works carried out by the authors in the field of structural and functional optimization of industrial robot's numerically controlled (NC) axes. The study includes the results obtained in the research stage of the experimental measurements performed to evaluate the electrical servomotor's thermal behavior using a thermal (infrared) imaging camera. The analyzed servomotor is a brushless servomotor integrated in an experimental stand for linear motion NC axis experimental research, existing in the MMS department from EMTS faculty. Supplementary to the driving servomotor, the experimental stand includes a belt drive transmission, a ball screw - bearings assembly and a driven element guided by ball rail system. This experimental research phase is part of the doctoral thesis of first author and was conducted in order to validate the mathematical models developed in the PhD thesis. Thus, experimental results presented in the paper have been used to validate first mathematical models for electric motor's preliminary selection and checking, (performed by determining the total reflected inertia of the mechanical system on motor shaft level) as well as the mathematical models for final selection and checking (by evaluating the servomotor's thermal energy dissipation, and servomotor's internal and external maximum operating temperature). Second, the experimental results have been used to validate the assisted simulation for structural and functional optimization of industrial robot's NC axes based on both servomotor and drive's thermal behavior analysis, performed in the thesis by means of a dedicated commercial software package.

Prediction of Cavitation Inception Within Regions of Flow Separation

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Eduard Amromin
Keyword(s):  
Experimental Data ◽  
Turbulent Flow ◽  
Flow Separation ◽  
Computational Method ◽  
Average Flow ◽  
Cavitation Inception ◽  
The Core ◽  
Good Agreement

Cavitation within regions of flow separation appears in drifting vortices. A two-part computational method is employed for prediction of cavitation inception number there. The first part is an analysis of the average flow in separation regions without consideration of an impact of vortices. The second part is an analysis of equilibrium of the bubble within the core of a vortex located in the turbulent flow of known average characteristics. Computed cavitation inception numbers for axisymmetric flows are in the good agreement with the known experimental data.

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