Investigation of a High Lift LP Turbine Blade Submitted to Passing Wakes: Part 2 — Boundary Layer Transition

2004 ◽  
Author(s):  
Thomas Coton ◽  
Tony Arts
Keyword(s):  
Boundary Layer ◽  
Fast Response ◽  
Boundary Layer Transition ◽  
Test Case ◽  
Layer Transition ◽  
High Lift ◽  
Multiple Interaction ◽  
Intermittency Factor ◽  
Lp Turbine ◽  
Exit Mach Number

A new test case for very high lift LP turbines has been investigated. The interaction with incoming wakes has been experimentally assessed at two Reynolds number values (13 and 30 × 104) and two inlet turbulence levels (0.8 and 3.5%) for an exit Mach number equal to 0.7. The blade performance was discussed in part 1 of the paper. Part 2 investigates the boundary layer transition and its interaction with the incoming wakes. The intermittency factor was computed from fast response wall heat transfer signals. In presence of passing wakes, the modeling was particularly improved by considering the effect of the velocity gradient on the wake impact. The space-time diagrams revealed complex multiple interaction zones. The calming phenomenon appeared weak compared to the influence of the wake negative jet and the re-establishment process of the separation region.

Investigation of a High Lift LP Turbine Blade Submitted to Passing Wakes: Part 1 — Profile Loss and Heat Transfer

2004 ◽  
Author(s):  
Thomas Coton ◽  
Tony Arts
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Separation Bubble ◽  
Suction Side ◽  
Rotating Disk ◽  
Boundary Layer Transition ◽  
Test Case ◽  
Layer Transition ◽  
High Lift ◽  
Exit Mach Number

A new test case for very high lift LP turbines has been investigated. The interaction with incoming wakes has been experimentally assessed at two Reynolds number values (13 and 30 × 104) and two inlet turbulence levels (0.8 and 3.5%) for an exit Mach number equal to 0.7. The wakes were generated by bars mounted on a rotating disk. Their features were varied in terms of diameter, rotational speed and number. In part 1 of the paper, the blade performance is discussed. Its evolution with the flow and wake parameters is mainly related to the variations of the boundary layer transition along the suction side. The beneficial effect of the wakes in suppressing the separation bubble could lead to a loss reduction of 36%. Distributions of the heat transfer coefficient and of higher order statistical variables support the discussion and constitute a quantitative database for LP turbines. The boundary layer behavior and its transitional aspects are particularly investigated in part 2.

An Experimental Investigation of Passive Control Device: Blade Wake Interaction on a Ultra High Lift Turbine Profile

2008 ◽  
Author(s):  
Daniele Simoni ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Francesco Bertini ◽  
Ennio Spano
Keyword(s):  
Boundary Layer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Passive Control ◽  
Control Device ◽  
Boundary Layer Transition ◽  
Critical Conditions ◽  
Ensemble Averaging ◽  
Layer Transition ◽  
High Lift

The transition of the boundary layer subjected to unsteady wake-passing in a linear cascade of ultra high lift profiles has been investigated at the Avio Aerodynamics Laboratory. The blade profiles are representative of the turbine nozzle mid section of a long range aeroengine. Measurements were performed at the cruise Reynolds number. A surface hot-film array was adopted to survey the boundary layer nature and the periodic variations related to the passing wakes. A phase-locked ensemble averaging technique was employed in order to separate the random fluctuations from the periodic ones. Results have been represented in space-time plots in order to provide an overall view of the time-dependent phenomena in terms of the quasi wall shear stress statistical moments, that are important parameters for the analysis of the boundary layer transition and separation. Passive control devices may be adopted to suppress boundary layer laminar separation at critical conditions (low Reynolds numbers, ultra high lift profiles). In the present experimental investigation a wavy step device has been mounted on the suction side of the blade. The effects of this boundary layer control device on the transition process and profile losses have been investigated at cruise Reynolds number, with and without incoming wakes.

Effects of boundary layer transition on the aerodynamic analysis of high-lift systems

2019 ◽  
Vol 90 ◽  
pp. 233-245 ◽  
Author(s):  
Gustavo Luiz Olichevis Halila ◽  
Alexandre Pequeno Antunes ◽  
Ricardo Galdino da Silva ◽  
João Luiz F. Azevedo
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
High Lift ◽  
Aerodynamic Analysis

Parametric Study of Fluidic Oscillators for Use in Active Boundary Layer Control

2011 ◽  
Author(s):  
Marion Mack ◽  
Reinhard Niehuis ◽  
Andreas Fiala
Keyword(s):  
Boundary Layer ◽  
Parametric Study ◽  
Pressure Ratio ◽  
Pressure Fluctuations ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Pressure Transducers ◽  
Tollmien Schlichting ◽  
Exit Mach Number

A parametric study was conducted to identify the main factors influencing the frequency produced by fluidic oscillators with the goal of using the actuator to trigger boundary layer transition through the excitation of Tollmien Schlichting waves. Test bench conditions were chosen to match the static pressure at the actuation position on the candidate blade profile for a cascade exit Mach number of 0.6 and Reynolds numbers from 60,000 to 200,000. The inlet vs. outlet pressure ratio and the position and geometry of the outlet holes were all varied. Additionally, the effect of the oscillator’s scale and the feedback channel geometry were considered. The flow at the exit was measured using a hot wire, while Kulite pressure transducers were used to measure pressure fluctuations within the device. This paper shows that fluidic oscillators can achieve frequencies of 10 kHz and that the parameters considered play an important role in the performance of these devices.

Flat-Plate Boundary Layers in Accelerated Flow

2016 ◽  
Author(s):  
Pascal Bader ◽  
Manuel Pschernig ◽  
Wolfgang Sanz ◽  
Jakob Woisetschläger ◽  
Franz Heitmeir ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Skin Friction ◽  
Boundary Layers ◽  
Laser Doppler Anemometry ◽  
Plate Boundary ◽  
Boundary Layer Transition ◽  
Test Case ◽  
Transitional Region ◽  
Layer Transition

Flow in turbomachines is generally highly turbulent. The boundary layers, however, often exhibit laminar-to-turbulent transition. But also relaminarization of the turbulent flow may occur. The state of the boundary layer is important, since it strongly influences transport phenomena like skin friction and heat transfer. It is therefore vitally important for the designer to understand the process of boundary layer transition and to determine the position of transition onset and the length of the transitional region. In order to get into the details of transition and relaminarization it is helpful to study simplified test cases first. Therefore, in this paper a relaminarization test case for a simple geometry is investigated: The boundary layer flow along a flat plate is exposed to acceleration with three different acceleration parameters, which is known as a crucial parameter for relaminarization. Measurements were performed for the inlet free-stream velocities of 5 m/s and 9 m/s. Several experimental techniques for detecting transition were tested at the institute before their application. In this work, Laser-Doppler anemometry (LDA) measurements were performed, since this optical technique is non-intrusive and does not disturb the flow. Therefore it can also be used in narrow flow passages where probe blockage can be crucial. As an outcome of this study, an insight into the process of relaminarization is presented. Although the key onset values for relaminarization stated in literature are fulfilled with the test setup, full relaminarization over the whole boundary layer has not been achieved. It seems, that using only the skin friction as indicator for relaminarization is not sufficient.

Prediction of Boundary-Layer Transition Effects on Turbine Airfoil Profile Losses

2003 ◽  
Author(s):  
D. Keith Walters ◽  
James H. Leylek
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Boundary Layer Transition ◽  
Navier Stokes ◽  
Test Case ◽  
Layer Transition ◽  
Airfoil Surface ◽  
New Model ◽  
User Input ◽  
Profile Losses

A previous paper by these authors demonstrated the ability of CFD simulations to accurately resolve profile losses — both with and without film cooling — for a test case in which the airfoil boundary layers were turbulent over the entire airfoil surface. The same paper highlighted the inability of currently available methods to properly resolve losses for cases in which the airfoil boundary layer undergoes transition. This paper presents new CFD results for the identical test case of flow through a linear turbine airfoil cascade. This test case matches an experimental study documented in the open literature, and the measured data is used for validation of the computational results. The Reynolds-averaged Navier-Stokes simulations were performed using a new three-equation eddy-viscosity turbulence model previously developed and documented by the authors. The new model has been developed specifically to provide accurate resolution of boundary-layer transition, without any need for empirical correlations or problem-dependent user input. Results obtained with the new model on the uncooled airfoil show a significant improvement in loss prediction over currently available models that cannot resolve boundary-layer transition. Results for the film-cooled cases show improvement over more traditional models, but highlight the need to incorporate the physics of separated shear-layer transition in addition to attached boundary-layer transition.

scholarly journals Boundary Layer Transition Under the Presence of Discrete Frequencies in the Freestream Turbulence Spectrum

1991 ◽  
Author(s):  
Jorge Costa ◽  
Tony Arts
Keyword(s):  
Boundary Layer ◽  
Excitation Frequency ◽  
Sampling Technique ◽  
Skin Friction Coefficient ◽  
Boundary Layer Transition ◽  
Test Surface ◽  
Decision Threshold ◽  
Layer Transition ◽  
Layer Flow ◽  
Intermittency Factor

The flow in turbomachines is characterized by a high turbulent activity; its spectrum frequently reveals energy peaks at privileged frequencies. Most often they influence the boundary layer transition onset. This type of forced transition was studied at the von Karman Institute in a low speed wind-tunnel along a flat test surface. Discrete frequency energy peaks were introduced into the mainstream flow by acoustic means. The receptivity of the boundary layer flow to the acoustic excitation frequency was put in evidence both by the frequency dependent transition Reynolds number and the streamwise intermittency factor distributions. The intermittency measurements were performed with the help of a conditional sampling technique; the later included a new approach to the positioning of the laminar-turbulent decision threshold. The growth of selected oscillation modes were compared in a natural and a forced transition situation. A model providing an estimation, within the transition region, of the turbulence level profiles and the skin friction coefficient was finally proposed.

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