Boundary-Layer Transition in Accelerating Flows With Intense Freestream Turbulence: Part 1—Disturbances Upstream of Transition Onset

1992 ◽  
Vol 114 (3) ◽  
pp. 313-321 ◽  
Author(s):  
M. F. Blair
Keyword(s):  
Boundary Layer ◽  
Outer Region ◽  
Streamwise Velocity ◽  
Boundary Layer Transition ◽  
Freestream Turbulence ◽  
Adiabatic Wall ◽  
Layer Transition ◽  
Frequency Distributions ◽  
Flow Acceleration ◽  
Mode Transitions

Hot-wire anemometry was employed to examine the laminar-to-turbulent transition of low-speed, two-dimensional boundary layers for two (moderate) levels of flow acceleration and various levels of grid-generated freestream turbulence. Flows with an adiabatic wall and with uniform-flux heat transfer were explored. All of the experimental test cases resulted in bypass-mode transitions, a conclusion based upon the observance of spots upstream of the theoretical minimum critical Reynolds number (three cases) or, for one case, upon the evidence that T-S mode amplification played no apparent role in the transition. Data obtained for the preonset stage indicate that the streamwise-component fluctuation-amplitude distributions, frequency distributions and outer-region waveforms of these bypass-mode transitions were similar to those reported in the literature for low-freestream-turbulence transitions. Within the zone upstream of the first appearance of turbulent spots: (1) The near-wall (Y<δ/2) fluctuations were predominantly low-frequency (frequency approximately 1/5 of that of the most amplified T-S disturbances). (2) The maximum streamwise-component fluctuations occurred over the altitude band 0.3<Y/δ<0.4. (3) Very strong negative “spikes” in streamwise velocity were observed, just upstream of spot initiation, at boundary-layer altitudes near Y/δ=0.6.

Boundary-Layer Transition in Accelerating Flows With Intense Freestream Turbulence: Part 2—The Zone of Intermittent Turbulence

1992 ◽  
Vol 114 (3) ◽  
pp. 322-332 ◽  
Author(s):  
M. F. Blair
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Boundary Layer Transition ◽  
Transitional Region ◽  
Freestream Turbulence ◽  
Intermittent Turbulence ◽  
Adiabatic Wall ◽  
Layer Transition ◽  
Flow Acceleration ◽  
Boundary Layer Turbulence

Hot-wire anemometry was employed to examine the laminar-to-turbulent transition of low-speed, two-dimensional boundary layers for two (moderate) levels of flow acceleration and various levels of grid-generated freestream turbulence. Flows with an adiabatic wall and with uniform-flux heat transfer were explored. Conditional discrimination techniques were employed to examine the zones of flow within the transitional region. This analysis demonstrated that as much as one-half of the streamwise-component unsteadiness, and much of the apparent anisotropy, observed near the wall was produced, not by turbulence, but by the steps in velocity between the turbulent and inter-turbulent zones of flow. Within the turbulent zones u′/v′ ratios were about equal to those expected for equilibrium boundary-layer turbulence. Near transition onset, however, the turbulence kinetic energy within the turbulent zones exceeded fully turbulent boundary-layer levels. Turbulent-zone power-spectral-density measurements indicate that the ratio of dissipation to production increased through transition. This suggests that the generation of the full equilibrium turbulent boundary-layer energy cascade required some time (distance) and may explain the very high TKE levels near onset.

Criteria for Boundary Layer Transition

2011 ◽  
Author(s):  
Stefan Becker ◽  
Donald M. McEligot ◽  
Edmond Walsh ◽  
Eckart Laurien
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Boundary Layer Flow ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Turbulence Level ◽  
Two Dimensional ◽  
Freestream Turbulence ◽  
Layer Transition ◽  
Layer Flow

New results are deduced to assess the validity of proposed transition indicators when applied to situations other than boundary layers on smooth surfaces. The geometry employed utilizes a two-dimensional square rib to disrupt the boundary layer flow. The objective is to determine whether some available criteria are consistent with the present measurements of laminar recovery and transition for the flow downstream of this rib. For the present data — the proposed values of thresholds for transition in existing literature that are based on the freestream turbulence level at the leading edge are not reached in the recovering laminar run but they are not exceeded in the transitioning run either. Of the pointwise proposals examined, values of the suggested quantity were consistent for three of the criteria; that is, they were less than the threshold in laminar recovery and greater than it in the transitioning case.

A “Laminar + Transition Criteria” Model for Hypersonic Three-Dimensional Boundary Layer Transition Prediction

2015 ◽  
Vol 798 ◽  
pp. 627-631 ◽  
Author(s):  
Ling Zhou ◽  
Chao Yan ◽  
Zi Hui Hao ◽  
Wei Xuan Kong
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Boundary Layer Transition ◽  
Blunt Cone ◽  
Layer Transition ◽  
Total Enthalpy ◽  
Transition Prediction ◽  
Transition Criteria ◽  
Dimensional Boundary

A “laminar + transition criteria” model utilizingReθ/MeandReCFcriteria in conjunction with an intermittency functionΓis developed in this paper. With pretreated computational grid and total enthalpyh0=(h0,∞)maxcriteria the boundary layer edge and crossflow velocity can be obtained by using parallel methodology. Validation is accomplished via HIFiRE-5 and a blunt cone with small angle of attack. Results show that computedReθ/MeandReCFdistributions are similar to theN-factor for streamwise instability and crossflow instability from linear PSE methods. The shape and trend of transition regions predicted by the “laminar + transition criteria” model in HIFiRE-5 and blunt cone are in good agreement with the experiment and DNS. However, for the transition induced by inflection point on streamwise velocity profiles, using criteria related to boundary layer thickness is inappropriate and can predict transition onset prematurely.

A Boundary Layer Transition Model

1996 ◽  
Author(s):  
Mark W. Johnson ◽  
Ali H. Ercan
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Transition ◽  
Test Cases ◽  
Length Scale ◽  
Transition Model ◽  
Freestream Turbulence ◽  
Layer Transition ◽  
Frequency Spectra ◽  
Low Frequencies ◽  
Turbulent Length Scale

A new boundary layer transition model is presented which relates the velocity fluctuations near the wall to the formation of turbulent spots. A relationship for the near wall velocity frequency spectra is also established, which indicates an increasing bias towards low frequencies as the skin friction coefficient for the boundary layer decreases. This result suggests that the dependence of transition on the turbulent length scale is greatest at low freestream turbulence levels. This transition model is incorporated in a conventional boundary layer integral technique and is used to predict eight of the ERCOFTAC test cases. Three of these test cases are for nominally zero pressure gradient and the remaining five are for a pressure distribution typical of an aft loaded turbine blade. The model is demonstrated to predict the development of the boundary layer through transition reasonably accurately for all the test cases. The sensitivity of start of transition to the turbulent length scale at low freestream turbulence levels is also demonstrated.

Experimental Investigation of Single Roughness Element Effects on Supersonic Boundary Layer Transition

2014 ◽  
Author(s):  
Henny Bottini ◽  
Bayindir H. Saracoglu ◽  
Guillermo Paniagua
Keyword(s):  
Boundary Layer ◽  
Wall Temperature ◽  
Roughness Element ◽  
Pressure Fluctuations ◽  
Supersonic Boundary Layer ◽  
Boundary Layer Transition ◽  
Adiabatic Wall ◽  
Layer Transition ◽  
Temperature And Pressure ◽  
Unsteady Effects

Predicting the characteristics of a transitional boundary layer remains an open challenge in supersonic flow fields. An experimental campaign to understand the effects of a single roughness element on a supersonic laminar boundary layer was designed. Two Mach numbers were tested, 1.6 and 2.3, including two roughness heights, 0.1 mm and 1 mm, over a flat plate. Steady and unsteady wall temperature and pressure levels were recorded to interpret the influence of the wake of the roughness. Heat flux and adiabatic wall temperature trends, temperature and pressure fluctuations RMS trends and time evolution of spectral content were reported. The initial wall temperature was varied during the wall temperature measurements and the resulting steady and unsteady effects on the roughness wake were investigated.

Effects of Large Scale High Freestream Turbulence, and Exit Reynolds Number on Turbine Vane Heat Transfer in a Transonic Cascade

2007 ◽  
Author(s):  
S. Nasir ◽  
J. S. Carullo ◽  
W. F. Ng ◽  
K. A. Thole ◽  
H. Wu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Large Scale ◽  
Suction Side ◽  
Boundary Layer Transition ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Layer Transition ◽  
Mach Numbers

This paper experimentally and numerically investigates the effect of large scale high freestream turbulence intensity and exit Reynolds number on the surface heat transfer distribution of a turbine vane in a 2-D linear cascade at realistic engine Mach numbers. A passive turbulence grid was used to generate a freestream turbulence level of 16% and integral length scale normalized by the vane pitch of 0.23 at the cascade inlet. The baseline turbulence level and integral length scale normalized by the vane pitch at the cascade inlet were measured to be 2% and 0.05, respectively. Surface heat transfer measurements were made at the midspan of the vane using thin film gauges. Experiments were performed at exit Mach numbers of 0.55, 0.75 and 1.01 which represent flow conditions below, near, and above nominal conditions. The exit Mach numbers tested correspond to exit Reynolds numbers of 9 × 105, 1.05 × 106, and 1.5 × 106, based on true chord. The experimental results showed that the large scale high freestream turbulence augmented the heat transfer on both the pressure and suction sides of the vane as compared to the low freestream turbulence case and promoted slightly earlier boundary layer transition on the suction surface for exit Mach 0.55 and 0.75. At nominal conditions, exit Mach 0.75, average heat transfer augmentations of 52% and 25% were observed on the pressure and suction side of the vane, respectively. An increased Reynolds number was found to induce earlier boundary layer transition on the vane suction surface and to increase heat transfer levels on the suction and pressure surfaces. On the suction side, the boundary layer transition length was also found to be affected by increase changes in Reynolds number. The experimental results also compared well with analytical correlations and CFD predictions.

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