scholarly journals An Inverse Design Method for Cascades for Low-Reynolds Number Flow

2012 ◽  
Vol 2012 ◽  
pp. 1-18 ◽  
Author(s):  
Martin Böhle
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Design Method ◽  
Low Reynolds Number ◽  
Design Procedure ◽  
Inverse Design ◽  
Suction Surface ◽  
Present Contribution ◽  
Reynolds Number Flow ◽  
Low Reynolds

Inverse design of cascades for low Reynolds number can be applied for the aerodynamic development of fans and compressors. The present contribution describes a complete design procedure by taking into account the transition from laminar to turbulent boundary layer flow. A shape factor distribution is prescribed along the suction surface of the blades. The inverse boundary layer calculation is performed by the application of a finite difference method. On the pressure side the velocity distribution is prescribed in such a way that the given flow angles in front of and behind the cascade are realized. An inverse calculation based on potential theory is applied in order to determine the geometry of the cascade. At the end of the present contribution a cascade is designed by the described inverse design procedure and the flow is simulated by the application of CFD.

Unsteady flow mechanism of the integrated aggressive inter-turbine duct in low Reynolds number condition

2020 ◽  
Vol 234 (9) ◽  
pp. 1507-1517
Author(s):  
Hongrui Liu ◽  
Jun Liu ◽  
Qiang Du ◽  
Guang Liu ◽  
Pei Wang
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Unsteady Flow ◽  
Low Reynolds Number ◽  
Low Pressure ◽  
Tip Clearance ◽  
Surface Boundary ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Low Reynolds

Aggressive inter-turbine duct, which has ultra-high bypass ratio and ultra-short axial length, is widely applied in the modern turbofan engine because it can reduce engine weight and improve low-pressure rotor dynamic characteristics. However, the aggressive inter-turbine duct that has swirling flow, wake, shock, and tip clearance leakage flow of upstream high-pressure turbine, and even has structs in its flow channel, is liable to separate, especially in high-altitude low Reynolds number (Re) condition. In addition, its downstream low-pressure turbine is on the edge of separation too. In this paper, an integrated aggressive inter-turbine duct embedded with wide-chord low-pressure turbine nozzle is adopted to eliminate the aggressive inter-turbine duct's end-wall separation. Since there are many studies on suppressing the blade suction surface's separation by upstream wake, in this study inherent wake is utilized to suppress the boundary layer separation on low-pressure turbine nozzle's suction surface in the integrated aggressive inter-turbine duct. The paper studies the unsteady flow mechanisms of the integrated aggressive inter-turbine duct (especially the separation and transition mechanisms of low-pressure turbine nozzle's suction surface boundary layer) by the computatioinal simulation method.

Numerical Simulation of Turbine Blade Boundary Layer and Heat Transfer and Assessment of Turbulence Models

1997 ◽  
Vol 119 (4) ◽  
pp. 794-801 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Bypass Transition ◽  
Boundary Layer Development ◽  
Low Reynolds ◽  
Layer Development

The boundary layer development and convective heat transfer on transonic turbine nozzle vanes are investigated using a compressible Navier–Stokes code with three low-Reynolds-number k–ε models. The mean-flow and turbulence transport equations are integrated by a four-stage Runge–Kutta scheme. Numerical predictions are compared with the experimental data acquired at Allison Engine Company. An assessment of the performance of various turbulence models is carried out. The two modes of transition, bypass transition and separation-induced transition, are studied comparatively. Effects of blade surface pressure gradients, free-stream turbulence level, and Reynolds number on the blade boundary layer development, particularly transition onset, are examined. Predictions from a parabolic boundary layer code are included for comparison with those from the elliptic Navier–Stokes code. The present study indicates that the turbine external heat transfer, under real engine conditions, can be predicted well by the Navier–Stokes procedure with the low-Reynolds-number k–ε models employed.

Low Reynolds number flow past a transverse cylinder at Mach two.

AIAA Journal ◽  
1972 ◽  
Vol 10 (10) ◽  
pp. 1381-1382
Author(s):  
CLARENCE W. KITCHENS ◽  
CLARENCE C. BUSH
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Low Reynolds Number Flow ◽  
Reynolds Number Flow ◽  
Flow Past ◽  
Number Flow ◽  
Low Reynolds

Experimental Comparison of DBD Plasma Actuators for Low Reynolds Number Separation Control

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Christopher R. Marks ◽  
Rolf Sondergaard ◽  
Mitch Wolff ◽  
Rich Anthony
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Turbine Blades ◽  
Plasma Actuators ◽  
Experimental Comparison ◽  
Separation Control ◽  
Suction Surface ◽  
Dbd Plasma ◽  
Low Reynolds ◽  
Low Reynolds Number Airfoil

This paper presents experimental work comparing several Dielectric Barrier Discharge (DBD) plasma actuator configurations for low Reynolds number separation control. Actuators studied here are being investigated for use in a closed loop separation control system. The plasma actuators were fabricated in the U.S. Air Force Research Laboratory Propulsion Directorate’s thin film laboratory and applied to a low Reynolds number airfoil that exhibits similar suction surface behavior to those observed on Low Pressure (LP) Turbine blades. In addition to typical asymmetric arrangements producing downstream jets, one electrode configurations was designed to produce an array of off axis jets, and one produced a spanwise array of linear vertical jets in order to generate vorticity and improved boundary layer to freestream mixing. The actuators were installed on an airfoil and their performance compared by flow visualization, surface stress sensitive film (S3F), and drag measurements. The experimental data provides a clear picture of the potential utility of each design. Experiments were carried out at four Reynolds numbers, 1.4 × 105, 1.0 × 105, 6.0 × 104, and 5.0 × 104 at a-1.5 deg angle of attack. Data was taken at the AFRL Propulsion Directorate’s Low Speed Wind Tunnel (LSWT) facility.

Numerical investigations on dynamic stall of low Reynolds number flow around oscillating airfoils

2010 ◽  
Vol 39 (9) ◽  
pp. 1529-1541 ◽  
Author(s):  
Shengyi Wang ◽  
Derek B. Ingham ◽  
Lin Ma ◽  
Mohamed Pourkashanian ◽  
Zhi Tao
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Dynamic Stall ◽  
Numerical Investigations ◽  
Low Reynolds Number Flow ◽  
Reynolds Number Flow ◽  
Number Flow ◽  
Low Reynolds

Optimal motion control of three-sphere based low-Reynolds number swimming microrobot

Robotica ◽  
2021 ◽  
pp. 1-17
Author(s):  
Hossein Nejat Pishkenari ◽  
Matin Mohebalhojeh
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Optimal Controller ◽  
Optimal Motion ◽  
Low Reynolds Number Flow ◽  
Reynolds Number Flow ◽  
Three Sphere ◽  
Low Reynolds Number Swimming ◽  
Number Flow ◽  
Low Reynolds

Abstract Microrobots with their promising applications are attracting a lot of attention currently. A microrobot with a triangular mechanism was previously proposed by scientists to overcome the motion limitations in a low-Reynolds number flow; however, the control of this swimmer for performing desired manoeuvres has not been studied yet. Here, we have proposed some strategies for controlling its position. Considering the constraints on arm lengths, we proposed an optimal controller based on quadratic programming. The simulation results demonstrate that the proposed optimal controller can steer the microrobot along the desired trajectory as well as minimize fluctuations of the actuators length.

Experimental and Numerical Investigation of Transition Effects on a Low Reynolds Number Airfoil

2017 ◽  
Author(s):  
Michael J. Collison ◽  
Peter X. L. Harley ◽  
Domenico di Cugno
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Low Reynolds Number ◽  
Flow Visualisation ◽  
Transition Model ◽  
Laminar Separation ◽  
Oil Flow ◽  
Low Reynolds ◽  
Low Reynolds Number Airfoil

Low speed, small scale turbomachinery operates at low Reynolds number with transition phenomena occurring. In small consumer product applications, high efficiency and low noise are key performance metrics. Transition behaviour will partly determine the state of the boundary layer at the trailing edge; whether it is laminar, turbulent or separated impacts aerodynamic and acoustic performance. This study aimed to evaluate a commercially available CFD transition model on a low Reynolds number Eppler E387 airfoil and identify whether it was able to correctly model the boundary layer transition, and at what expense. CFD was carried out utilising the ANSYS Shear Stress Transport (SST) k-ω γ-Reθ transition model. The CFD progressed from 2D in Fluent v150, through to single cell thickness 3D (pseudo 2D) in CFX v172. An Eppler E387 low Reynolds number airfoil, for which experimental data was readily available from literature at Re = 200,000 was used as the validation case for the CFD, with results computed at numerous incidence angles and mesh densities. Additionally, experimental surface oil flow visualisation was undertaken in a wind tunnel using a scaled E387 airfoil for the zero incidence case at Re = 50,000. The flow visualisation exhibited the expected key features of transition in the breakdown of the boundary layer from laminar to turbulent, and was used as a validation case for the CFD transition model. The comparison between the results from the CFD transition model and the experimental data from literature suggested varying levels of agreement based on the mesh density and CFD solver in the starting location of the laminar separation bubble, with higher disparity for the position of the reattachment point. Whether 2D or 3D, the prediction accuracy was seen to worsen at high incidence angles. Finally, the location of the laminar separation bubble between CFD and oil flow visualisation had good agreement and a set of guidelines on the mesh parameters which can be applied to low Reynolds number turbomachinery simulations was determined.

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