scholarly journals Study on Oil-Film Interferometry Measurement Technique of Hypersonic Boundary Layer Transition

2018 ◽  
Vol 36 (6) ◽  
pp. 1156-1161
Author(s):  
Hao Dong ◽  
Shicheng Liu ◽  
Xi Geng ◽  
Keming Cheng
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Skin Friction ◽  
High Speed ◽  
Smooth Surface ◽  
Roughness Element ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Oil Film ◽  
Hypersonic Wind Tunnel

Prediction of boundary layer transition is important for the design of hypersonic aircrafts. The study of boundary layer transition of hypersonic flow around a flat plate using oil-film interferometry was investigated at Φ500mm traditional hypersonic wind tunnel. In order to measure the skin friction fast and precisely on the hypersonic wind tunnel, the traditional oil-film interferometry technique is improved. A high-speed camera is used to capture the images of fringes and the viscosity of the silicon oil is modified according to the wall temperature measured by thermocouples during the test. The skin frictions of smooth surface and the surface with single square roughness element were measured. For the smooth surface, the boundary layer is laminar. However, the boundary layer transition is promoted by wake vortices induced by the roughness element. Both the results of skin friction with and without the roughness element are in good agreement with the simulation results correspondingly, indicating high accuracy of the oil film interferometry technique.

Hypersonic Wind-Tunnel Measurements of Boundary-Layer Transition on a Slender Cone

AIAA Journal ◽  
2016 ◽  
Vol 54 (4) ◽  
pp. 1250-1263 ◽  
Author(s):  
Katya M. Casper ◽  
Steven J. Beresh ◽  
John F. Henfling ◽  
Russell W. Spillers ◽  
Brian O. M. Pruett ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Hypersonic Wind Tunnel ◽  
Wind Tunnel Measurements

High-speed boundary-layer transition induced by a discrete roughness element

2013 ◽  
Vol 729 ◽  
pp. 524-562 ◽  
Author(s):  
Prahladh S. Iyer ◽  
Krishnan Mahesh
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
High Speed ◽  
Roughness Element ◽  
Transition Process ◽  
Significant Rise ◽  
Boundary Layer Transition ◽  
Streamwise Vortices ◽  
Layer Transition ◽  
Mach Numbers

AbstractDirect numerical simulation (DNS) is used to study laminar to turbulent transition induced by a discrete hemispherical roughness element in a high-speed laminar boundary layer. The simulations are performed under conditions matching the experiments of Danehy et al. (AIAA Paper 2009–394, 2009) for free-stream Mach numbers of 3.37, 5.26 and 8.23. It is observed that the Mach 8.23 flow remains laminar downstream of the roughness, while the lower Mach numbers undergo transition. The Mach 3.37 flow undergoes transition closer to the bump when compared with Mach 5.26, in agreement with experimental observations. Transition is accompanied by an increase in ${C}_{f} $ and ${C}_{h} $ (Stanton number). Even for the case that did not undergo transition (Mach 8.23), streamwise vortices induced by the roughness cause a significant rise in ${C}_{f} $ until 20$D$ downstream. The mean van Driest transformed velocity and Reynolds stress for Mach 3.37 and 5.26 show good agreement with available data. Temporal spectra of pressure for Mach 3.37 show that frequencies in the range of 10–1000 kHz are dominant. The transition process involves the following key elements: upon interaction with the roughness element, the boundary layer separates to form a series of spanwise vortices upstream of the roughness and a separation shear layer. The system of spanwise vortices wrap around the roughness element in the form of horseshoe/necklace vortices to yield a system of counter-rotating streamwise vortices downstream of the element. These vortices are located beneath the separation shear layer and perturb it, which results in the formation of trains of hairpin-shaped vortices further downstream of the roughness for the cases that undergo transition. These hairpins spread in the span with increasing downstream distance and the flow increasingly resembles a fully developed turbulent boundary layer. A local Reynolds number based on the wall properties is seen to correlate with the onset of transition for the cases considered.

Influence of distributed roughness elements on boundary layer transition for NACA0012 airfoil

2018 ◽  
Vol 32 (29) ◽  
pp. 1850349 ◽  
Author(s):  
Hao Dong ◽  
Shicheng Liu ◽  
Xi Geng ◽  
Kun Zhang ◽  
Keming Cheng
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Wind Tunnel ◽  
Skin Friction Coefficient ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Supersonic Wind Tunnel ◽  
Oil Film ◽  
Naca0012 Airfoil ◽  
Roughness Elements

The influence of distributed cylinder roughness elements on boundary layer transition for NACA0012 airfoil at Ma = 0.6 has been investigated by subsonic/transonic/supersonic wind tunnel experiment with oil-film interferometry. Three different heights and two different distances of cylinder roughness elements on the airfoil model were used, and the skin friction coefficient was measured by the oil-film interferometry. The experimental results show that higher roughness elements promote the transition earlier. In addition, narrower distance of roughness elements can delay the transition compared with the case of wider distance.

scholarly journals Experimental Investigation of the Boundary Layer Transition on a Laminar Airfoil Using Infrared Thermography

2018 ◽  
Vol 180 ◽  
pp. 02040
Author(s):  
Tomáš Jelínek
Keyword(s):  
Boundary Layer ◽  
Experimental Investigation ◽  
Wind Tunnel ◽  
Infrared Thermography ◽  
High Speed ◽  
Turbulent Boundary Layers ◽  
Boundary Layer Transition ◽  
Wind Tunnel Testing ◽  
Layer Transition ◽  
Displacement Thickness

The transition in the boundary layer is investigated using infrared thermography (IRT). The study is carried out on a laminar airfoil in the transonic intermittent in-draft wind tunnel. The transition in the boundary layer is evocated using transition-generator strips of different thicknesses at two Mach numbers: 0.4 and 0.8. The tested transition-generators thickness to boundary layer displacement thickness ratio was from 0.42 to 1.25. The Reynolds number respect to the airfoil chord is: Re = 1.0 – 1.4·106. The six cases for different transition-generators thickness ratios were compared. The behaviours of laminar and turbulent boundary layers are discussed. The use of IRT has been proven to be an appropriate tool for detecting the transition of the boundary layer in high-speed wind tunnel testing.

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