scholarly journals Measurement of the boundary layer transition point over a 2-D LFC airfoil in transonic flow by liquid crystals

1994 ◽  
Vol 14 (Supplement1) ◽  
pp. 115-118
Author(s):  
Masayoshi Noguchi ◽  
Norikazu Sudani ◽  
Yoji Ishida ◽  
Mamoru Sato ◽  
Hiroshi Kanda
Keyword(s):  
Boundary Layer ◽  
Liquid Crystals ◽  
Transonic Flow ◽  
Transition Point ◽  
Boundary Layer Transition ◽  
Layer Transition

Numerical study of boundary layer transition using intermittency model

2019 ◽  
Vol 91 (8) ◽  
pp. 1156-1168 ◽  
Author(s):  
Massoud Tatar ◽  
Mojtaba Tahani ◽  
Mehran Masdari
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Transport Equation ◽  
Transition Point ◽  
Static Pressure ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Content Type ◽  
Reduced Frequency ◽  
Pressure Suction

Purpose In this paper, the applicability of shear stress transport k-ω model along with the intermittency concept has been investigated over pitching airfoils to capture the laminar separation bubble (LSB) position and the boundary layer transition movement. The effect of reduced frequency of oscillations on boundary layer response is also examined. Design/methodology/approach A two-dimensional computational fluid dynamic code was developed to compute the effects of unsteadiness on LSB formation, transition point movement, pressure distribution and lift force over an oscillating airfoil using transport equation of intermittency accompanied by the k-ω model. Findings The results indicate that increasing the angle of attack over the stationary airfoil causes the LSB size to shorten, leading to a rise in wall shear stress and pressure suction peak. In unsteady cases, both three- and four-equation models are capable of capturing the experimentally measured transition point well. The transition is delayed for an unsteady boundary layer in comparison with that for a static airfoil at the same angle of attack. Increasing the unsteadiness of flow, i.e. reduced frequency, moves the transition point toward the trailing edge of the airfoil. This increment also results in lower static pressure suction peak and hence lower lift produced by the airfoil. It was also found that the fully turbulent k-ω shear–stress transport (SST) model cannot capture the so-called figure-of-eight region in lift coefficient and the employment of intermittency transport equation is essential. Practical implications Boundary layer transition and unsteady flow characteristics owing to airfoil motion are both important for many engineering applications including micro air vehicles as well as helicopter blade, wind turbine and aircraft maneuvers. In this paper, the accuracy of transition modeling based on intermittency transport concept and the response of boundary layer to unsteadiness are investigated. Originality/value As a conclusion, the contribution of this paper is to assess the ability of intermittency transport models to predict LSB and transition point movements, static pressure distribution and aerodynamic lift variations and boundary layer flow pattern over dynamic pitching airfoils with regard to oscillation frequency effects for engineering problems.

Transonic Drag Prediction on a DLR-F6 Transport Configuration

2012 ◽  
Vol 566 ◽  
pp. 676-679
Author(s):  
Qiu Ya Zheng ◽  
Jian Hu Feng ◽  
Zun Huan Shen
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Transonic Flow ◽  
Flow Fields ◽  
Boundary Layer Transition ◽  
Grid Refinement ◽  
Layer Transition ◽  
Total Drag ◽  
Drag Prediction ◽  
Block Structured

The accuracy of the drag prediction is investigated by simulating the transonic flow fields around the DLR-F6 wing-body (WB) and wing-body-nacelle-pylon (WNP) configurations. A series of coarse, medium, and fine density multi-block structured patched grids for both the DLR-F6 WB and WBNP configurations are employed to examine effect of grid on forces and incremental drag by adding the nacelle and pylon. The effect of boundary layer transition specification on the drag and incremental drag are also estimated. The results show that grid refinement decrease WB total drag by 6.8 drag counts, WBNP total drag by 15.3 drag counts. Specifying transition reduce WB total drag by 9.7 drag counts, WBNP total drag by 11 drag counts as compared to fully turbulent boundary layer computations, but transition has little effects on nacelle/pylon incremental drag.

On boundary-layer transition in transonic flow

1993 ◽  
Vol 27 (3) ◽  
pp. 309-342 ◽  
Author(s):  
R. I. Bowles ◽  
F. T. Smith
Keyword(s):  
Boundary Layer ◽  
Transonic Flow ◽  
Boundary Layer Transition ◽  
Layer Transition

An Investigation on the Onset of Wake-Induced Transition and Turbulent Spot Production Rate Using Thermochromic Liquid Crystals

1999 ◽  
Author(s):  
C. Kittichaikarn ◽  
P. T. Ireland ◽  
S. Zhong ◽  
H. P. Hodson
Keyword(s):  
Boundary Layer ◽  
Liquid Crystals ◽  
Flat Plate ◽  
Laminar Boundary Layer ◽  
Gas Turbines ◽  
Formation Rate ◽  
Boundary Layer Transition ◽  
Published Data ◽  
Layer Transition ◽  
Turbulent Spots

Wakes shed by upstream blade rows are known to cause boundary layer transition in both the compressor and turbine stages of axial flow gas turbines. This transition process is believed to take place via discrete zones of turbulence known as turbulent spots which occur in an otherwise laminar boundary layer. However, the process of transition over the blade surface cannot, at present, be reliably predicted. This is due to a lack of information on where and when these turbulent spots form and how they grow and merge as they convect downstream to form the turbulent boundary layer. This paper presents detailed experimental information on the process of boundary layer transition induced by a bar generated wake travelling over a zero pressure gradient laminar boundary layer on a flat plate. The Reynolds number was 3×105. The peak turbulence intensity within the wakes varied from 3 to 6 % by using different bar of different diameters. An encapsulated cholesteric liquid crystals coating has been employed on a heated flat plate to reveal detailed information over the full surface. The information includes the thermal characteristics, the spot onset and formation rate. Data were obtained at high resolution on a grid of 30,000 points. The results were compared to intermittency plots and time-distance diagrams obtained by using surface-mounted thin film gauges and found to be similar. The data were also consistent with well established correlations and other published data from the literature for existing wake-induced transition models.

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