Investigation of the Effectiveness of Various Types of Boundary Layer Transition Elements of Low Reynolds Number Turbine Bladings

2004 ◽  
Author(s):  
Claus H. Sieverding ◽  
Carlo Bagnera ◽  
A. C. Boege ◽  
Juan A. Cordero Anto`n ◽  
Vincent Lue`re
Keyword(s):  
Boundary Layer ◽  
Guide Vane ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Boundary Layer Separation ◽  
Boundary Layer Transition ◽  
Transition Elements ◽  
Layer Transition ◽  
Optimum Position ◽  
Low Reynolds

The paper describes an experimental investigation of the use of different types of boundary layer transition elements for the control of boundary layer separation at low Reynolds numbers. The tests are carried out in a low speed cascade tunnel for Reynolds numbers between 30000 and 200000. For convenience the author used an existing HP turbine guide vane with ∼63 degree turning. To obtain representative adverse pressure gradients as those existing on the rear suction side of highly loaded LP blades the tests are run at a pitch-to-chord ratio of 1. The transition elements include tripwires, single and double rows of spherical roughness elements, balloon type transition elements and a metal sheet actuated by shape memory alloy springs. The optimum position and height of the transition elements are obtained with systematic tests with the trip wire. All other elements are placed at the same position and have approximately the same height. As expected, the transition elements are very beneficial at low Re numbers but deteriorate the performance at high Re numbers. The advantages and drawbacks of the various configurations are discussed and suggestions for real turbine applications are made.

Numerical Study of Wall Influence on Boundary-Layer Transition for Two-Dimensional NACA 16-012 and 4412 Hydrofoil Sections

1990 ◽  
Vol 34 (01) ◽  
pp. 38-47
Author(s):  
R. Latorre ◽  
R. Baubeau
Keyword(s):  
Boundary Layer ◽  
Test Section ◽  
Numerical Study ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Turbulent Separation ◽  
Side Pressure ◽  
Effective Angle

One of the difficulties in hydrofoil model tests is the relatively low Reynolds number of the test piece and the presence of the test section walls. This paper presents the results of systematic calculations of the potential flow field of NA 4412 and NACA 16-012 hydrofoil in a test section with wall-to-chord ratios h/c -1.0. The corresponding boundary-layer calculations using the CERT calculation scheme are presented to show the influence of the nearby walls on shifting the location of the boundary-layer laminar-turbulent separation as well as turbulent separation. By introducing an effective angle of attack, it is possible to obtain close agreement in the calculated and measured suction side pressure distortion as well as the locations of the boundary-layer separation and transition.

Predicting Separation and Transitional Flow in Turbine Blades at Low Reynolds Numbers—Part I: Development of Prediction Methodology

2010 ◽  
Vol 133 (3) ◽  
Author(s):  
Darius D. Sanders ◽  
Walter F. O’Brien ◽  
Rolf Sondergaard ◽  
Marc D. Polanka ◽  
Douglas C. Rabe
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Model ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Transitional Flow ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Low Reynolds ◽  
And Performance

There is an increasing interest in design methods and performance prediction for aircraft engine turbines operating at low Reynolds numbers. In this regime, boundary layer separation may be more likely to occur in the turbine flow passages. For accurate computational fluid dynamics (CFD) predictions of the flow, correct modeling of laminar-turbulent boundary layer transition is essential to capture the details of the flow. To investigate possible improvements in model fidelity, CFD models were created for the flow over two low pressure turbine blade designs. A new three-equation eddy-viscosity type turbulent transitional flow model, originally developed by Walters and Leylek (2004, “A New Model for Boundary Layer Transition Using a Single Point RANS Approach,” ASME J. Turbomach., 126(1), pp. 193–202), was employed for the current Reynolds averaged Navier–Stokes (RANS) CFD calculations. Previous studies demonstrated the ability of this model to accurately predict separation and boundary layer transition characteristics of low Reynolds number flows. The present research tested the capability of CFD with the Walters and Leylek turbulent transitional flow model to predict the boundary layer behavior and performance of two different turbine cascade configurations. Flows over low pressure turbine (LPT) blade airfoils with different blade loading characteristics were simulated over a Reynolds number range of 15,000–100,000 and predictions were compared with experimental cascade results. Part I of this paper discusses the prediction methodology that was developed and its validation using a lightly loaded LPT blade airfoil design. The turbulent transitional flow model sensitivity to turbulent flow parameters was investigated and showed a strong dependence on freestream turbulence intensity with a second-order effect of turbulent length scale. Focusing on the calculation of the total pressure loss coefficients to judge performance, the CFD simulation incorporating Walters and Leylek’s turbulent transitional flow model produced adequate prediction of the Reynolds number performance for the lightly loaded LPT blade cascade geometry. Significant improvements in performance were shown over predictions of conventional RANS turbulence models. Historically, these models cannot adequately predict boundary layer transition.

Predicting Separation and Transitional Flow in Turbine Blades at Low Reynolds Numbers

2008 ◽  
Author(s):  
Darius D. Sanders ◽  
Walter F. O’Brien ◽  
Rolf Sondergaard ◽  
Marc D. Polanka ◽  
Douglas C. Rabe
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Model ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Transitional Flow ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Low Reynolds ◽  
And Performance

There is increasing interest in design methods and performance prediction for aircraft engine turbines operating at low Reynolds numbers. In this regime, boundary layer separation may be more likely to occur in the turbine flow passages. For accurate CFD predictions of the flow, correct modeling of laminar-turbulent boundary layer transition is essential to capture the details of the flow. To investigate possible improvements in model fidelity, CFD models were created for the flow over two low pressure turbine blade designs. A new three-equation eddy-viscosity type turbulent transitional flow model originally developed by Walters and Leylek was employed for the current RANS CFD calculations. Previous studies demonstrated the ability of this model to accurately predict separation and boundary layer transition characteristics of low Reynolds number flows. The present research tested the capability of CFD with the Walters and Leylek turbulent transitional flow model to predict the boundary layer behavior and performance of two different turbine cascade configurations. Flows over the Pack-B turbine blade airfoil and the midspan section of a typical low pressure turbine (TLPT) blade were simulated over a Reynolds number range of 15,000–100,000, and predictions were compared to experimental cascade results. The turbulent transitional flow model sensitivity to turbulent flow parameters was investigated and showed a strong dependence on free-stream turbulence intensity with a second order effect of turbulent length scale. Focusing on the calculation of the total pressure loss coefficients to judge performance, the CFD simulation incorporating Walters and Leylek’s turbulent transitional flow model produced adequate prediction of the Reynolds number performance for the TLPT blade cascade geometry. Furthermore, the correct qualitative flow response to separated shear was observed for the Pack-B blade airfoil. Significant improvements in performance predictions were shown over predictions of conventional RANS turbulence models that cannot adequately model boundary layer transition.

Effects of Reynolds Number and Free-Stream Turbulence on Boundary Layer Transition in a Compressor Cascade

2000 ◽  
Author(s):  
Heinz-Adolf Schreiber ◽  
Wolfgang Steinert ◽  
Bernhard Küsters
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Bypass Transition ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
High Reynolds Numbers ◽  
High Turbulence ◽  
High Reynolds

An experimental and analytical study has been performed on the effect of Reynolds number and free-stream turbulence on boundary layer transition location on the suction surface of a controlled diffusion airfoil (CDA). The experiments were conducted in a rectilinear cascade facility at Reynolds numbers between 0.7 and 3.0×106 and turbulence intensities from about 0.7 to 4%. An oil streak technique and liquid crystal coatings were used to visualize the boundary layer state. For small turbulence levels and all Reynolds numbers tested the accelerated front portion of the blade is laminar and transition occurs within a laminar separation bubble shortly after the maximum velocity near 35–40% of chord. For high turbulence levels (Tu > 3%) and high Reynolds numbers transition propagates upstream into the accelerated front portion of the CDA blade. For those conditions, the sensitivity to surface roughness increases considerably and at Tu = 4% bypass transition is observed near 7–10% of chord. Experimental results are compared to theoretical predictions using the transition model which is implemented in the MISES code of Youngren and Drela. Overall the results indicate that early bypass transition at high turbulence levels must alter the profile velocity distribution for compressor blades that are designed and optimized for high Reynolds numbers.

scholarly journals Compressible Direct Numerical Simulation of Low-Pressure Turbines: Part I — Methodology

2014 ◽  
Author(s):  
Richard D. Sandberg ◽  
Richard Pichler ◽  
Liwei Chen ◽  
Roderick Johnstone ◽  
Vittorio Michelassi
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Direct Numerical Simulation ◽  
Environmental Parameters ◽  
Boundary Layer Separation ◽  
Low Pressure ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Laminar Separation ◽  
Background Turbulence

Modern low pressure turbines (LPT) feature high pressure ratios and moderate Mach and Reynolds numbers, increasing the possibility of laminar boundary-layer separation on the blades. Upstream disturbances including background turbulence and incoming wakes have a profound effect on the behavior of separation bubbles and the type/location of laminar-turbulent transition and therefore need to be considered in LPT design. URANS are often found inadequate to resolve the complex wake dynamics and impact of these environmental parameters on the boundary layers and may not drive the design to the best aerodynamic efficiency. LES can partly improve the accuracy, but has difficulties in predicting boundary layer transition and capturing the delay of laminar separation with varying inlet turbulence levels. Direct Numerical Simulation (DNS) is able to overcome these limitations but has to date been considered too computationally expensive. Here a novel compressible DNS code is presented and validated, promising to make DNS practical for LPT studies. Also, the sensitivity of wake loss coefficient with respect to freestream turbulence levels below 1% is discussed.

An Experimental Study of Heat Transfer on an Outlet Guide Vane

2014 ◽  
Author(s):  
Chenglong Wang ◽  
Lei Wang ◽  
Bengt Sundén ◽  
Valery Chernoray ◽  
Hans Abrahamsson
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Guide Vane ◽  
Incidence Angle ◽  
Boundary Layer Transition ◽  
Transfer Coefficients ◽  
Suction Surface ◽  
Layer Transition

In the present study, the heat transfer characteristics on the suction and pressure sides of an outlet guide vane (OGV) are investigated by using liquid crystal thermography (LCT) method in a linear cascade. Because the OGV has a complex curved surface, it is necessary to calibrate the LCT by taking into account the effect of viewing angles of the camera. Based on the calibration results, heat transfer measurements of the OGV were conducted. Both on- and off-design conditions were tested, where the incidence angles of the OGV were 25 degrees and −25 degrees, respectively. The Reynolds numbers, based on the axial flow velocity and the chord length, were 300,000 and 450,000. In addition, heat transfer on suction side of the OGV with +40 degrees incidence angle was measured. The results indicate that the Reynolds number and incidence angle have considerable influences upon the heat transfer on both pressure and suction surfaces. For on-design conditions, laminar-turbulent boundary layer transitions are on both sides, but no flow separation occurs; on the contrary, for off-design conditions, the position of laminar-turbulent boundary layer transition is significantly displaced downstream on the suction surface, and a separation occurs from the leading edge on the pressure surface. As expected, larger Reynolds number gives higher heat transfer coefficients on both sides of the OGV.

Velocity and Pressure Measurements Along a Row of Confined Cylinders

2006 ◽  
Author(s):  
Barton L. Smith ◽  
Jack J. Stepan ◽  
Donald M. McEligot
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Symmetry Plane ◽  
Field Measurements ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Recirculation Region ◽  
Pressure Measurements ◽  
Layer Transition ◽  
Flow Experiments

The results of flow experiments performed in a cylinder array designed to mimic a VHTR Nuclear Plant lower plenum design are presented. Pressure drop and velocity field measurements were made. Based on these measurements, five regimes of behavior are identified that are found to depend on Reynolds number. It is found that the recirculation region behind the cylinders is shorter than that of half cylinders placed on the wall representing the symmetry plane. Unlike a single cylinder, the separation point is found to always be on the rear of the cylinders, even at very low Reynolds number. Boundary layer transition is found to occur at much lower Reynolds numbers than previously reported.

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