Euler Solutions for Transonic Oscillating Cascade Flows Using Dynamic Triangular Meshes

1995 ◽  
Vol 117 (3) ◽  
pp. 393-400 ◽  
Author(s):  
C. J. Hwang ◽  
S. Y. Yang
Keyword(s):  
Experimental Data ◽  
Phase Angle ◽  
Transonic Flow ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Oscillation Amplitude ◽  
Time History ◽  
Present Approach ◽  
Instantaneous Pressure ◽  
Interblade Phase Angle

The modified total-variation-diminishing scheme and an improved dynamic triangular mesh algorithm are presented to investigate the transonic oscillating cascade flows. In a Cartesian coordinate system, the unsteady Euler equations are solved. To validate the accuracy of the present approach, transonic flow around a single NACA 0012 airfoil pitching harmonically about the quarter chord is computed first. The calculated instantaneous pressure coefficient distribution during a cycle of motion compare well with the related numerical and experimental data. To evaluate further the present approach involving nonzero interblade phase angle, the calculations of transonic flow around an oscillating cascade of two unstaggered NACA 0006 blades with interblade phase angle equal to 180 deg are performed. From the instantaneous pressure coefficient distributions and time history of lift coefficient, the present approach, where a simple spatial treatment is utilized on the periodic boundaries, gives satisfactory results. By using this solution procedure, transonic flows around an oscillating cascade of four biconvex blades with different oscillation amplitudes, reduced frequencies, and interblade phase angles are investigated. From the distributions of magnitude and phase angle of the dynamic pressure difference coefficient, the present numerical results show better agreement with the experimental data than those from the linearized theory in most of the cases. For every quarter of one cycle, the pressure contours repeat and proceed one pitch distance in the upward or downward direction for interblade phase angle equal to −90 deg or 90 deg, respectively. The unsteady pressure wave and shock behaviors are observed. From the lift coefficient distributions, it is further confirmed that the oscillation amplitude, interblade phase angle, and reduced frequency all have significant effects on the transonic oscillating cascade flows.

scholarly journals Euler Solutions for Transonic Oscillating Cascade Flows Using Dynamic Triangular Meshes

1993 ◽  
Author(s):  
C. J. Hwang ◽  
S. Y. Yang
Keyword(s):  
Experimental Data ◽  
Phase Angle ◽  
Transonic Flow ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Oscillation Amplitude ◽  
Time History ◽  
Present Approach ◽  
Instantaneous Pressure ◽  
Interblade Phase Angle

The modified total-variation-diminishing scheme and an improved dynamic triangular mesh algorithm are presented to investigate the transonic oscillating cascade flows. In a Cartesian coordinate system, the unsteady Euler equations are solved. To validate the accuracy of the present approach, transonic flow around single NACA 0012 airfoil pitching harmonically about the quarter chord is computed first. The calculated instantaneous pressure coefficient distributions during a cycle of motion compare well with the related numerical and experimental data. To further evaluate the present approach involving nonzero interblade phase angle, the calculations of transonic flow around oscillating cascade of two unstaggered NACA 0006 blades with interblade phase angle equal to 180 deg are performed. From the instantaneous pressure coefficient distributions and time history of lift coefficient, the present approach, where a simple spatial treatment is utilized on the periodic boundaries, gives satisfactory results. By using the above solution procedure, transonic flows around oscillating cascade of four biconvex blades with different oscillation amplitudes, reduced frequencies and interblade phase angles are investigated. From the distributions of magnitude and phase angle of the dynamic pressure difference coefficient, the present numerical results show better agreement with the experimental data than those from the linearized theory in most of the cases. For every quarter of one cycle, the pressure contours repeat and proceed one pitch distance in the upward or downward direction for interblade phase angle equal to −90 deg or 90 deg, respectively. The unsteady pressure wave and shock behaviors are observed. From the lift coefficient distributions, it is further confirmed that the oscillation amplitude, interblade phase angle and reduced frequency all have significant effects on the transonic oscillating cascade flows.

Near-Bed Flow Mechanisms Around a Circular Marine Pipeline Close to a Flat Seabed in the Subcritical Flow Regime Using a k-ɛ Model

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Muk Chen Ong ◽  
Torbjørn Utnes ◽  
Lars Erik ◽  
Dag Myrhaug ◽  
Bjørnar Pettersen
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Flow Regime ◽  
Boundary Layer Thickness ◽  
Friction Velocity ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Mean Pressure ◽  
Flow Mechanisms ◽  
The Mean

Flow mechanisms around a two-dimensional (2D) circular marine pipeline close to a flat seabed have been investigated using the 2D unsteady Reynolds-averaged Navier–Stokes (URANS) equations with a standard high Reynolds number k-ɛ model. The Reynolds number (based on the free stream velocity and cylinder diameter) ranges from 1 × 104 to 4.8 × 104 in the subcritical flow regime. The objective of the present study is to show a thorough documentation of the applicability of the k-ɛ model for engineering design within this flow regime by means of a careful comparison with available experimental data. The inflow boundary layer thickness and the Reynolds numbers in the present simulations are set according to published experimental data, with which the simulations are compared. Detailed comparisons with the experimental data for small gap ratios are provided and discussed. The effects of the gap to diameter ratio and the inflow boundary layer thickness have been studied. Although under-predictions of the essential hydrodynamic quantities (e.g., time-averaged drag coefficient, time-averaged lift coefficient, root-mean-square fluctuating lift coefficient, and mean pressure coefficient at the back of the pipeline) are observed due to the limitation of the turbulence model, the present approach is capable of providing good qualitative agreement with the published experimental data. The vortex shedding mechanisms have been investigated, and satisfactory predictions are obtained. The mean pressure coefficient and the mean friction velocity along the flat seabed are predicted reasonably well as compared with published experimental and numerical results. The mean seabed friction velocity at the gap is much larger for small gaps than for large gaps; thus, the bedload sediment transport is much larger for small gaps than for large gaps.

A Numerical Investigation of the Response of an Elastically Mounted Rigid Cylinder With Two Degrees of Freedom

2010 ◽  
Author(s):  
Bruno C. Ferreira ◽  
Marcelo A. Vitola ◽  
Juan B. V. Wanderley ◽  
Sergio H. Sphaier ◽  
Carlos A. Levi
Keyword(s):  
Experimental Data ◽  
Phase Angle ◽  
Degrees Of Freedom ◽  
Stokes Equations ◽  
Lift Coefficient ◽  
The Body ◽  
Curvilinear Coordinates ◽  
Two Degrees Of Freedom ◽  
Conservative Scheme ◽  
Rigid Cylinder

The vortex induced vibration (VIV) on a circular cylinder is investigated by the numerical solution of the Reynolds average Navier-Stokes equations. An upwind and Total Variation Diminishing (TVD) conservative scheme is used to solve the governing equations written in curvilinear coordinates and the k–ε turbulence model is used to simulate the turbulent flow in the wake of the body. The cylinder is supported by a spring and a damper and free to vibrate in the transverse and in-line directions. In previous work, numerical results for the amplitude of oscillation, vortex shedding frequency, and phase angle between lift and displacement were compared to experimental data obtained from Khalak and Williamson (1996) to validate the code for VIV simulations in the transverse direction. In the present work, results are obtained for phase angle, amplitude, frequency, and lift coefficient and compared to experimental data from Jauvtis and Williamson (2003) for an elastically mounted rigid cylinder with two degrees of freedom. Differences in the amplitude of oscillation between experimental and numerical data were observed for both direction. It seems that the fluid flow memory effect is an important aspect that should be taken in consideration on numerical simulation to reproduce the experimental results for VIV with 2DOF as pointed out by Moe and Wu [1].

scholarly journals Unsteady Simulation of Transonic Buffet of a Supercritical Airfoil with Shock Control Bump

Aerospace ◽  
2021 ◽  
Vol 8 (8) ◽  
pp. 203
Author(s):  
Yufei Zhang ◽  
Pu Yang ◽  
Runze Li ◽  
Haixin Chen
Keyword(s):  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Flow Characteristics ◽  
Control Effect ◽  
Shock Control Bump ◽  
Shock Control ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Unsteady Simulation ◽  
Drag Ratio

The unsteady flow characteristics of a supercritical OAT15A airfoil with a shock control bump were numerically studied by a wall-modeled large eddy simulation. The numerical method was first validated by the buffet and nonbuffet cases of the baseline OAT15A airfoil. Both the pressure coefficient and velocity fluctuation coincided well with the experimental data. Then, four different shock control bumps were numerically tested. A bump of height h/c = 0.008 and location xB/c = 0.55 demonstrated a good buffet control effect. The lift-to-drag ratio of the buffet case was increased by 5.9%, and the root mean square of the lift coefficient fluctuation was decreased by 67.6%. Detailed time-averaged flow quantities and instantaneous flow fields were analyzed to demonstrate the flow phenomenon of the shock control bumps. The results demonstrate that an appropriate “λ” shockwave pattern caused by the bump is important for the flow control effect.

Explanation of the Influence of Inflow Air Content on the Lift of Cavitating Hydrofoils

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Eduard Amromin
Keyword(s):  
Experimental Data ◽  
Theoretical Study ◽  
Lift Coefficient ◽  
Cavity Surface ◽  
Air Bubbles ◽  
Incoming Flow ◽  
Fluid Density ◽  
Air Content ◽  
Theoretical Results ◽  
Good Agreement

According to several known experiments, an increase of the incoming flow air content can increase the hydrofoil lift coefficient. The presented theoretical study shows that such increase is associated with the decrease of the fluid density at the cavity surface. This decrease is caused by entrainment of air bubbles to the cavity from the surrounding flow. The theoretical results based on such explanation are in a good agreement with the earlier published experimental data for NACA0015.

Separation in oscillating laminar boundary-layer flows

1971 ◽  
Vol 47 (1) ◽  
pp. 21-31 ◽  
Author(s):  
R. A. Despard ◽  
J. A. Miller
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Reverse Flow ◽  
Oscillation Amplitude ◽  
Hot Wire ◽  
Boundary Layer Flows ◽  
Laminar Boundary Layers ◽  
History Of

The results of an experimental investigation of separation in oscillating laminar boundary layers is reported. Instantaneous velocity profiles obtained with multiple hot-wire anemometer arrays reveal that the onset of wake formation is preceded by the initial vanishing of shear at the wall, or reverse flow, throughout the entire cycle of oscillation. Correlation of the experimental data indicates that the frequency, Reynolds number and dynamic history of the boundary layer are the dominant parameters and oscillation amplitude has a negligible effect on separation-point displacement.

Experimental study of a pitching and plunging wing

2018 ◽  
Vol 90 (7) ◽  
pp. 1136-1144 ◽  
Author(s):  
Dimitris Gkiolas ◽  
Demetri Yiasemides ◽  
Demetri Mathioulakis
Keyword(s):  
Experimental Data ◽  
Flow Visualization ◽  
Wind Turbine ◽  
Flow Separation ◽  
Flow Behavior ◽  
Lift Coefficient ◽  
Turbine Blades ◽  
Content Type ◽  
Separation Line ◽  
Wing Chord

Purpose The complex flow behavior over an oscillating aerodynamic body, e.g. a helicopter rotor blade, a rotating wind turbine blade or the wing of a maneuvering airplane involves combinations of pitching and plunging motions. As the parameters of the problem (Re, St and phase difference between these two motions) vary, a quasi-steady analysis fails to provide realistic results for the aerodynamic response of the moving body, whereas this study aims to provide reliable experimental data. Design/methodology/approach In the present study, a pitching and plunging mechanism was designed and built in a subsonic closed-circuit wind tunnel as well as a rectangular aluminum wing of a 2:1 aspect-ratio with a NACA64-418 airfoil, used in wind turbine blades. To measure the pressure distribution along the wing chord, a number of fast responding transducers were embedded into the mid span wing surface. Simultaneous pressure measurements were conducted along the wing chord for the Reynolds number of 0.85 × 106 for both steady and unsteady cases (pitching and plunging). A flow visualization technique was used to detect the flow separation line under steady conditions. Findings Elevated pressure fluctuations coincide with the flow separation line having been detected through surface flow visualization and flattened pressure distributions appear downstream of the flow separation line. Closed hysteresis loops of the lift coefficient versus angle of attack were measured for combined pitching and plunging motions. Practical implications The experimental data can be used for improvement of unsteady fluid mechanics problem solvers. Originality/value In the present study, a new installation was built allowing the aerodynamic study of oscillating wings performing pitching and plunging motions with prescribed frequencies and phase lags between the two motions. The experimental data can be used for improvement of computational fluid dynamics codes in case that the examined aerodynamic body is oscillating.

Starting System for Darrieus Water Turbine of Tidal Stream Electricity Generation

2016 ◽  
Author(s):  
Seiji Shimizu ◽  
Masayuki Fujii ◽  
Tetsuya Sumida ◽  
Kenji Sasa ◽  
Yasuhiro Kimura ◽  
...  
Keyword(s):  
Experimental Data ◽  
Cross Section ◽  
Electricity Generation ◽  
Lift Coefficient ◽  
Vertical Axis ◽  
Cylindrical Shape ◽  
Water Turbine ◽  
Tidal Stream ◽  
Tidal Stream Turbine ◽  
Original Experimental Data

Darrieus type vertical axis water turbine in a cylindrical shape which consists of some straight blades is simple, efficient and easy to install a generator upward. However, it has difficulty in starting revolution. As a method to cope with such a problem, a starting revolution assist mechanism was fabricated and set on a prototype of the turbine. Assist experiment was carried out. It resulted helping well the starting revolution. The improved prototype of tidal stream turbine can generate 1.4 W under a water flow of 1 m/s where impossible to self-start. Besides that, Darrieus water turbine’s generating torque property was investigated by the famous original experimental data of lift coefficient Cl and drag coefficient Cd for straight blades of NACA63 3-018 cross section. It was found that setting two or four blades in a turbine would help to improve the difficulty of starting revolution.

scholarly journals Design and Testing of a LUT Airfoil for Straight-Bladed Vertical Axis Wind Turbines

2018 ◽  
Vol 8 (11) ◽  
pp. 2266 ◽  
Author(s):  
Shoutu Li ◽  
Ye Li ◽  
Congxin Yang ◽  
Xuyao Zhang ◽  
Qing Wang ◽  
...  
Keyword(s):  
Wind Turbines ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Vertical Axis ◽  
Reynolds Numbers ◽  
Optimization Method ◽  
Geometrical Parameters ◽  
Vertical Axis Wind Turbines ◽  
University Of Technology ◽  
Horizontal Axis Wind Turbines

The airfoil plays an important role in improving the performance of wind turbines. However, there is less research dedicated to the airfoils for Vertical Axis Wind Turbines (VAWTs) compared to the research on Horizontal Axis Wind Turbines (HAWTs). With the objective of maximizing the aerodynamic performance of the airfoil by optimizing its geometrical parameters and by considering the law of motion of VAWTs, a new airfoil, designated the LUT airfoil (Lanzhou University of Technology), was designed for lift-driven VAWTs by employing the sequential quadratic programming optimization method. Afterwards, the pressure on the surface of the airfoil and the flow velocity were measured in steady conditions by employing wind tunnel experiments and particle image velocimetry technology. Then, the distribution of the pressure coefficient and aerodynamic loads were analyzed for the LUT airfoil under free transition. The results show that the LUT airfoil has a moderate thickness (20.77%) and moderate camber (1.11%). Moreover, compared to the airfoils commonly used for VAWTs, the LUT airfoil, with a wide drag bucket and gentle stall performance, achieves a higher maximum lift coefficient and lift–drag ratios at the Reynolds numbers 3 × 105 and 5 × 105.

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