Diagnostics of boundary layer transition by shear stress sensitive liquid crystals

2016 ◽  
Author(s):  
E. S. Shapoval
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Liquid Crystals ◽  
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.

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.

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

scholarly journals Vane Clocking Effects on Stator Suction Side Boundary Layers in a Multistage Compressor

2016 ◽  
Vol 2016 ◽  
pp. 1-14 ◽  
Author(s):  
Natalie R. Smith ◽  
Nicole L. Key
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Suction Side ◽  
Secondary Flows ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Boundary Layer Development ◽  
Multistage Compressor ◽  
Vane Clocking ◽  
The Impact

The stator inlet flow field in a multistage compressor varies in the pitchwise direction due to upstream vane wakes and how those wakes interact with the upstream rotor tip leakage flows. If successive vane rows have the same count, then vane clocking can be used to position the downstream vane in the optimum circumferential position for minimum vane loss. This paper explores vane clocking effects on the suction side vane boundary layer development by measuring the quasi-wall shear stress on the downstream vane at three spanwise locations. Comparisons between the boundary layer transition on Stator 1 and Stator 2 are made to emphasize the impact of rotor-rotor interactions which are not present for Stator 1 and yet contribute significantly to transition on Stator 2. Vane clocking can move the boundary layer transition in the path between the wakes by up to 24% of the suction side length at midspan by altering the influence of the Rotor 1 wakes in the 3/rev modulation from rotor-rotor interactions. The boundary layer near the vane hub and tip experiences earlier transition and separation due to interactions with the secondary flows along the shrouded endwalls. Flow visualization and Stator 2 wakes support the shear stress results.

scholarly journals Numerical study on the influence of wall temperature gradient on aerodynamic characteristics of low aspect ratio flying wing configuration

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Peng Lin ◽  
Xueqiang Liu ◽  
Neng Xiong ◽  
Xiaobing Wang ◽  
Ma Shang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Shear Stress ◽  
Aspect Ratio ◽  
Wall Temperature ◽  
Boundary Layer Transition ◽  
Wall Friction ◽  
Friction Drag ◽  
Layer Transition ◽  
Low Aspect Ratio

AbstractWith the aim for a low-aspect-ratio flying wing configuration, this study explores the influence of wall temperature gradient on the laminar and turbulent boundary layers of aircraft surface and determines the effect on the transition Reynolds number and wall friction drag. A four-equation turbulence model with transition mode is used to numerically simulate the flow around the model. The variation of wall friction coefficient, transition Reynolds number, and turbulent boundary layer flow with wall temperature are emphatically investigated. Results show that when the wall temperature increases from 288 to 500 K, the boundary layer transition Reynolds number for the wing section increased by approximately 28% and the surface friction drags decreases by approximately 10.7%. The hot wall enhances the viscous effects of the laminar temperature boundary layer, reduces the Reynolds shear stress and turbulent kinetic energy, and increases the flow stability. However, the velocity gradient and shear stress in the bottom of the turbulent boundary layer decreases, which leads to reduced friction shear stress on the wall surface. Therefore, for the low-aspect-ratio flying wing model, the hot wall can delay the boundary layer transition and reduce the friction drag coefficient in the turbulent region.

Sign in / Sign up

Export Citation Format

Share Document