scholarly journals Flow transition to turbulence and induced acoustics at Mach 6

2021 ◽  
Vol 33 (7) ◽  
pp. 076112
Author(s):  
Dimitris Drikakis ◽  
Konstantinos Ritos ◽  
S. Michael Spottswood ◽  
Zachary B. Riley
Keyword(s):  
Transition To Turbulence ◽  
Flow Transition

scholarly journals Separated-Flow Transition: Part 3 — Primary Modes and Vortex Dynamics

1998 ◽  
Author(s):  
Anca Hatman ◽  
Ting Wang
Keyword(s):  
Shear Layer ◽  
Boundary Layers ◽  
Separated Flow ◽  
Vortex Sheet ◽  
Separation Point ◽  
Transition To Turbulence ◽  
Flow Transition ◽  
Maximum Displacement ◽  
Laminar Separation ◽  
Separated Shear Layer

This paper clearly identifies the possible modes of transition in the separated boundary layers and their specific characteristics. This study distinguishes between the short and long bubbles primarily based on the separated flow structure. A hypothetical description of the vortex structure and evolution for each separated-flow transition mode is provided. The present approach in analyzing separated-flow transition is based on the assumption that the transition to turbulence in separated boundary layers is a result of the superposition of the effects of two different types of instability. The first type of instability is the Kelvin-Helmholtz (KH) instability. It occurs and develops in the shear layer at a specific location downstream of the separation point. The concentration of spanwise vorticity grows in time and remains in place through the vortex sheet roll-up mechanism. The roll-up vortex interacts with the wall and induces periodic ejection of near-wall fluid into the separated shear layer. The ejection process takes place at a location identifiable by the maximum displacement of shear layer, xMD. The second type of instability is the (convective) Tollmien-Schlichting (TS) instability. It originates in the boundary layer prior to the separation point and continues to evolve in the separated shear layer. The mechanism for the TS instability also leads to roll-ups, but it involves viscous tuning of the instability waves. Thus, the separated-flow transition is the result of spatially developing, often competing instabilities. The ejection induces the onset of transition for laminar short and long bubble modes of transition and controls the mid-transition point of transitional separation mode. The ejection may be accompanied by vortex shedding. Shedding occurs in the laminar separation - short bubble mode and occasionally in the transitional separation mode; however, it is not present in the laminar separation - long bubble mode of transition.

Modeling Laminar-to-Turbulent Transition in a Low-Pressure Turbine Flow Which Is Unsteady Due to Passing Wakes: Part I — Transition Onset

2003 ◽  
Author(s):  
Nan Jiang ◽  
Terrence W. Simon
Keyword(s):  
Phase Angle ◽  
Separated Flow ◽  
Low Pressure ◽  
Companion Paper ◽  
Transition To Turbulence ◽  
Flow Transition ◽  
Path Modeling ◽  
Suction Surface ◽  
Attached Flow ◽  
Wake Passing

The open literature on modeling transition to turbulence of boundary layer flows in low-pressure turbines is reviewed. Included are the separated flow transition onset models of Mayle and of Davis et al. and the attached flow transition onset models of Mayle, Abu-Ghannam and Shaw and Drela. Their results are applied against data previously taken at the University of Minnesota (UMN) to assess their performance for use on the suction surface of a turbine blade in the presence of passing wakes. The data show measurements of velocity, turbulence level, intermittency and spatial and temporal acceleration resolved in space and phase angle within the wake passing period. In a “quasi-static” comparison, the input values to the models are values taken from the experiment, resolved in phase angle within the wake-passing period. Predictions from the models (the flow states with regard to transition throughout the wake-passing period) are compared with instantaneous intermittency values taken from the experiment. The Mayle separated and attached flow onset models are shown to be successful for the case investigated when applied in that fashion. The Abu-Ghannam and Shaw and Drela transition onset models predict onset locations which are somewhat downstream of where the data indicate the transition onset to be. Unique characteristics regarding transition observed at different times in a wake passing cycle are discussed. Some reasons are given to explain the differences between experimental results and model predictions. Transition onset modeling is addressed in the present paper and transition path modeling is addressed in a companion paper (part II).

EXPERIMENTAL INVESTIGATION OF FLOW RESPONSE TO STATIONARY DISTURBANCE IN ROTATING-DISK FLOW

2019 ◽  
Vol XVI (2) ◽  
pp. 13-22
Author(s):  
Muhammad Ehtisham Siddiqui
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Three Dimensional ◽  
Rotating Disk ◽  
Careful Analysis ◽  
Laboratory Frame ◽  
Transition To Turbulence ◽  
Turbulent Regime ◽  
Mean Velocity ◽  
Layer Flow

Three-dimensional boundary-layer flow is well known for its abrupt and sharp transition from laminar to turbulent regime. The presented study is a first attempt to achieve the target of delaying the natural transition to turbulence. The behaviour of two different shaped and sized stationary disturbances (in the laboratory frame) on the rotating-disk boundary layer flow is investigated. These disturbances are placed at dimensionless radial location (Rf = 340) which lies within the convectively unstable zone over a rotating-disk. Mean velocity profiles were measured using constant-temperature hot-wire anemometry. By careful analysis of experimental data, the instability of these disturbance wakes and its estimated orientation within the boundary-layer were investigated.

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