Unsteady Separation on Lifting Surfaces

1987 ◽  
Vol 40 (4) ◽  
pp. 441-453 ◽  
Author(s):  
Mohamed Gad-el-Hak
Keyword(s):  
Three Dimensional ◽  
Leading Edge ◽  
Subject Area ◽  
Complex Flow ◽  
Vast Number ◽  
Freestream Velocity ◽  
Unsteady Separation ◽  
Aspect Ratios ◽  
Local Shear ◽  
Lifting Surfaces

This article presents a review of some recent work that deals with the phenomenon of unsteady separation on two- and three-dimensional lifting surfaces. The presently available experimental data are interpreted in light of the recent idea advanced by Ho (1986), in which unsteady separation is associated with a spatially developing local shear layer. No attempt is made to give a complete account of the vast number of papers written in the subject area. Instead, reference is made to a few excellent review articles available in the open literature. The unsteady motions considered include change of angle of attack, impulsive start from rest, and change of freestream velocity. The lifting surfaces studied are bodies of revolution and wings of different aspect ratios, planforms, and leading edge bluntness. Other, nonlifting surfaces are briefly considered. Velocity probe measurements in such complex flow fields are sparse. However, flow visualization results are ample and are extensively reviewed in this paper.

The Effect of Aspect Ratio on Wall Pressure Fluctuations at a Wing-Plate Junction

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
M. Awasthi ◽  
J. Rowlands ◽  
D. J. Moreau ◽  
C. J. Doolan
Keyword(s):  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Leading Edge ◽  
Suction Side ◽  
Wide Frequency Range ◽  
Wall Pressure ◽  
Frequency Range ◽  
Three Dimensional Flow ◽  
Wall Pressure Fluctuations ◽  
Aspect Ratios

Abstract Measurements of the wall pressure fluctuations near a wing-plate junction were made for wings with three different aspect ratios (AR) of 0.2, 0.5, and 1.0 at several angles of attack. The chord-based Reynolds number for each wing was 274,000. The results show that the wall pressure fluctuations are a function of wing AR for cases where AR≤ 1.0. For each wing, the pressure fluctuations are highest upstream of the wing leading-edge due to three-dimensional flow separation; wings with AR = 1.0 and 0.5 show comparable levels, while those with AR = 0.2 show lower fluctuation levels over a wide frequency range. Downstream of the leading-edge, the pressure fluctuations decay rapidly on both sides of the wing until the maximum thickness location after which little variation is observed. The pressure fluctuations downstream of the leading-edge on the suction-side were observed to be comparable for AR = 0.2 and 0.5, while those for AR = 1.0 were higher in magnitude. On the pressure-side, the pressure fluctuations near the leading-edge are a weak function of AR; however, those further downstream remain independent of AR. The pressure fluctuations aft of the wing on the suction-side are more coherent for lower ARs and show higher convection velocity, possibly due to an interaction between the tip and the junction flows for lower ARs.

scholarly journals Unsteady Aerodynamic Characteristics Simulations of Rotor Airfoil under Oscillating Freestream Velocity

2020 ◽  
Vol 10 (5) ◽  
pp. 1822
Author(s):  
Qing Wang ◽  
Qijun Zhao
Keyword(s):  
Three Dimensional ◽  
Grid Method ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Critical Value ◽  
Dynamic Stall ◽  
Navier Stokes ◽  
Freestream Velocity ◽  
Unsteady Aerodynamic ◽  
Edge Vortex

The dynamic stall characteristics of rotor airfoil are researched by employing unsteady Reynolds-Averaged Navier-Stokes (RANS) method under oscillating freestream velocity conditions. In order to simulate the oscillating freestream velocity of airfoil under dynamic stall conditions, the moving-embedded grid method is employed to simulate the oscillating velocity. By comparing the simulated dynamic stall characteristics of two-dimensional airfoil and three-dimensional rotor, it is indicated that the dynamic stall characteristics of airfoil under oscillating freestream velocity reflect the actual dynamic stall characteristics of rotor airfoil in forward flight more accurately. By comparing the simulated results of OA209 airfoil under coupled freestream velocity/pitching oscillation conditions, it is indicated that the dynamic stall characteristics of airfoil associate with the critical value of Cp peaks (i.e., the dynamic stall characteristics of OA209 airfoil would be enhanced when the maximum negative pressure is larger than −1.08, and suppressed when this value is smaller than −1.08). By comparing the characteristics of vortices under different oscillating velocities, it indicates that the dissipation rate of leading edge vortex presents as exponent characteristics, and it is not sensitive to different oscillating velocities.

Detailed Three-Dimensional Velocity Field Measurements of a Complex Internal Cooling Flow Within a Gas Turbine Vane

2019 ◽  
Author(s):  
Michael J. Benson ◽  
David Helmer ◽  
Bret P. Van Poppel ◽  
Benjamin Duhaime ◽  
David Bindon ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Three Dimensional ◽  
Leading Edge ◽  
Scale Model ◽  
Internal Cooling ◽  
Complex Flow ◽  
Copper Sulfate Solution ◽  
Flow Rates ◽  
Experimental Apparatus ◽  
Turbine Vane

Abstract A 6.67 scale model of the Advanced Recirculation Total Impingement Cooling (ARTIC) gas turbine vane insert’s leading edge was designed, built using stereolithography (SLA) fabrication methods, and tested using Magnetic Resonance Velocimetry (MRV), a non-invasive data acquisition technique that captures three-dimensional, three-component velocity fields of a copper sulfate solution over the course of several hours. The experimental apparatus supplied constant flow rates through a test section placed within a 3.0 Tesla MRI magnet. Tests were run at two fully turbulent flow rates corresponding to Reynolds numbers based on hydraulic diameter of 10,000 and 20,000 with the higher flow rate case achieving dynamic similarity with the full-scale ARTIC device. The experimental results elucidated key details and intricacies of the complex flow within the insert. Analysis of flow distribution between each of the three independent impingement zones revealed a degree of measurable jet to jet variability. Stagnation and recirculation zones were detected, informing design modifications and enabling assessment of inlet effects on impingement. Measurement uncertainty was assessed and estimated to be approximately 7.5% of the peak velocity at the inlet to the central feed cavity.

scholarly journals Investigation on Dynamic Stresses of Pump-Turbine Runner during Start Up in Turbine Mode

Processes ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 499
Author(s):  
Funan Chen ◽  
Huili Bi ◽  
Soo-Hwang Ahn ◽  
Zhongyu Mao ◽  
Yongyao Luo ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Unsteady Flow ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Leading Edge ◽  
Complex Flow ◽  
Dynamic Stresses ◽  
Start Up ◽  
Pumped Storage ◽  
Turbine Mode

The startup process occurs frequently for pumped storage units. During this process, the rotating rate that changes rapidly and unsteady flow in runner cause the complex dynamic response of runner, sometimes even resonance. The sharp rise of stress and the large-amplitude dynamic stresses of runner will greatly shorten the fatigue life. Thus, the study of start-up process in turbine mode is critical to the safety operation. This paper introduced a method of coupling one dimensional (1D) pipeline calculation and three-dimensional computational dynamics (3D CFD) simulation to analyze transient unsteady flow in units and to obtain more accurate and reliable dynamic stresses results during start up process. According to the results, stress of the ring near fixed support increased quickly as rotating rate rose and became larger than at fillets of leading edge and band in the later stages of start-up. In addition, it was found that dynamic response can be caused by rotor stator interaction (RSI), but also could even be generated by the severe pressure fluctuation in clearance, which can also be a leading factor of dynamic stresses. This study will facilitate further estimation of dynamic stresses in complex flow and changing rotating rate cases, as well as fatigue analysis of runner during transient operation.

Three Dimensional Measurements of a Turbine Blade Using Magnetic Resonance Thermometry and Magnetic Resonance Velocimetry

2017 ◽  
Author(s):  
Elliott T. Williams ◽  
Daniel C. Caniano ◽  
Gregory Davis ◽  
Angus M. Ferrell ◽  
Michael J. Benson ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Turbulent Flows ◽  
Turbine Blade ◽  
Three Dimensional ◽  
Leading Edge ◽  
Optical Measurements ◽  
Internal Cooling ◽  
Complex Flow ◽  
Full Field ◽  
Magnetic Resonance Velocimetry

A hollowed NACA-0012 airfoil with removable inserts was developed to study the complex flow through two interior chambers. The geometry represented an internally cooled gas turbine blade with internal impingement in several locations. A fully turbulent water flow passed the airfoil. Within the airfoil, a second fluid at a different temperature was mixed through the insert nearest the leading edge and recirculated to the aft chamber for additional internal cooling before exiting the airfoil as film cooling on the suction side and at the trailing edge. Time-averaged, three-dimensional temperature and three-component velocity measurements were collected using Magnetic Resonance Imagery (MRI) based techniques. Magnetic Resonance Velocimetry (MRV) and Thermometry (MRT) are techniques for measuring the velocity and temperature of fully turbulent flows at sub-millimeter-scale resolution. The benefits of these techniques over similar measuring techniques include the ability to collect full-field, three-dimensional, nonintrusive, non-optical measurements for conjugate heat transfer simulation validation in complex, turbulent flows. Multiple MRI-based techniques can be combined within the same experiment to explore the interaction between the mean fields of multiple quantities. The experimental setup employed in this work produced time-averaged velocity and temperature data illustrating flow details through the airfoil’s interior chambers and heat flux through the entire airfoil and at specific locations.

Three-Dimensional Planing at High Froude Number

1971 ◽  
Vol 15 (03) ◽  
pp. 221-230 ◽  
Author(s):  
D. P. Wang ◽  
P. Rispin
Keyword(s):  
Aspect Ratio ◽  
Pressure Distribution ◽  
Froude Number ◽  
Order Term ◽  
Lift Coefficient ◽  
Three Dimensional ◽  
Steady Motion ◽  
Iteration Process ◽  
Leading Edge ◽  
Aspect Ratios

The steady motion of a planing surface of moderate aspect ratio at small angles of attack is considered. Linearized theory is used with a square-root type of pressure singularity representing the flow near the leading edge. An asymptotic solution for the pressure distribution on the planing surface at large Froude number (or small β, the inverse of the Froude number) is sought. The lowest-order term of the pressure distribution, obtained by setting β equal to zero, is found to be the same as the pressure distribution on the lower side of the corresponding thin wing. Higher-order terms in β are obtained by an iteration process. Explicit solutions are obtained to order β2 for rectangular planforms. Numerical results are calculated for rectangular flat plate planing surfaces of aspect ratios from 0.5 to 2.0. It is found that for large aspect ratios the lift coefficient is reduced by the gravity effect and for small aspect ratios it is increased, the dividing aspect ratio being about 1.5. The results compare reasonably well with experimental data.

Characteristics of Bluff Body Stabilized Turbulent Premixed Flames

2011 ◽  
Author(s):  
Alejandro M. Briones ◽  
Balu Sekar ◽  
Hugh Thornburg
Keyword(s):  
Bluff Body ◽  
Three Dimensional ◽  
Leading Edge ◽  
Reacting Flows ◽  
Chemical Mechanism ◽  
Reacting Flow ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Aspect Ratios ◽  
Trailing Edges

Non-reacting and reacting flows past typical flameholders are modeled with URANS and LES. The continuity, momentum, energy, species, and turbulence governing equations are solved using two- and three-dimensional configurations. Either 2-step global or 44-step reduced chemical mechanism for C3H8-air combustion, accounting for turbulence-chemistry interaction, and with temperature- and species-dependent thermodynamic and transport properties is utilized. For square and rectangular bluff bodies the flow separates at the leading edges, whereas for triangular bluff body separation occurs only at the trailing edges. These bluff bodies exhibit two shear layers at the trailing edges that shed asymmetric vortices. For rectangular bluff bodies with aspect ratios (AR) less than 2.3 there is backflow from the wake. With increasing AR from unity, backflow is gradually diminished, and the von Ka´rma´n Strouhal number (StvK) decreases. For 2.0<AR<2.3, StvK jumps to a higher value and separation again occurs at the trailing edges for AR = 2.3. Further increase in AR decreases StvK again. The simulations with URANS qualitatively and quantitatively match experimental results for StvK vs. AR. Quantitative discrepancies are, however, found for AR≥2.3. In addition, two-dimensional non-reacting flows with URANS are sufficient to predict StvK. Moreover, two-dimensional simulations of reacting flow indicate that the flame promotes static and dynamic stability for AR = 1.0 and 2.3. The flame is dynamically unstable for AR = 2.0, exhibiting a von Ka´rma´n flow pattern. Stable flames anchored at the most downstream separation location (e.g., the flame anchored at AR = 1.0 is attached to the leading edge, whereas that of AR = 2.3 is attached to the trailing edge). Realizable k-ε URANS and LES simulations for the triangular cylinder closely match the experimental StvK for both non-reacting and reacting flows. Nonetheless, LES predicts a smaller recirculation length than k-ε URANS. LES predicts a flow field in which Be´rnard/von Ka´rma´n (BvK) instability is suppressed, whereas URANS predicts a competition between the Kelvin-Helmholtz (KH) instability and BvK.

Navier-Stokes Simulation of the Flow Around a Leading Edge Film-Cooled Turbine Blade Including the Interior Cooling System and Comparison With Experimental Data

1996 ◽  
Author(s):  
Dirk T. Vogel
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Turbine Blade ◽  
Cooling System ◽  
Three Dimensional ◽  
Leading Edge ◽  
Navier Stokes ◽  
Complex Flow ◽  
Three Dimensional Flow ◽  
Dimensional Flow

The three dimensional flow around an extensively investigated slot film cooled turbine blade is numerically investigated using a multi block finite volume Navier-Stokes solver. Three blowing rates are simulated including the whole geometry of the interior blade cooling system and slots. Due to the ejection at the blade leading edge and the geometry of the cooling slots a very complex turbulent three dimensional flow field is generated. The size and shape of the flow separation zones depending on the film cooling ejection is systematically investigated using several two-equation models, e.g. the standard and low Reynolds k–ε-Model of Lam and Bremhorst (1981) r[4], the extension of Kato/Launder (1993) [3] and the k–ω-Model of Wilcox (1991) [10], whereas the results of the standard k–ε-Model are presented. Experimental data obtained by Laser velocimetry, oil-flow pictures and pressure probes are used to understand the complex flow field and to validate the Navier-Stokes solver. The multi-block code applies a traditional Jameson type solver and an implicit solver using several spatial discretization schemes for the convective fluxes. The two-equation models are solved using an RED-BLACK implicit technique with first order spatial upwind discretization to guarantee stability.

A Three-Dimensional Model for the Prediction of Shock Losses in Compressor Blade Rows

1983 ◽  
Author(s):  
Arthur J. Wennerstrom ◽  
Steven L. Puterbaugh
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Leading Edge ◽  
Compressor Blade ◽  
Turbine Engines ◽  
Test Case ◽  
Three Dimensional Model ◽  
Aspect Ratios ◽  
Flow Effects ◽  
Shock Loss

A design trend evident in newly evolving aircraft turbine engines is a reduction in the aspect ratio of blading employed in fans, compressors, and turbines. As aspect ratio is reduced, various three-dimensional flow effects become significant which at higher aspect ratios could safely be neglected. This paper presents a new model for predicting the shock loss through a transonic or supersonic compressor blade row operating at peak efficiency. It differs from the classical Miller-Lewis-Hartmann normal shock model by taking into account the spanwise obliquity of the shock surface due to leading-edge sweep, blade twist, and solidity variation. The model is evaluated in combination with two test cases. Each was a low-aspect-ratio transonic stage which had exceeded its efficiency goals. Use of the revised shock loss model contributed 2.11 points to the efficiency of the first test case and 1.08 points to the efficiency of the second.

A Three-Dimensional Model for the Prediction of Shock Losses in Compressor Blade Rows

1984 ◽  
Vol 106 (2) ◽  
pp. 295-299 ◽  
Author(s):  
A. J. Wennerstrom ◽  
S. L. Puterbaugh
Keyword(s):  
Aspect Ratio ◽  
Three Dimensional ◽  
Leading Edge ◽  
Compressor Blade ◽  
Turbine Engines ◽  
Test Case ◽  
Three Dimensional Model ◽  
Aspect Ratios ◽  
Flow Effects ◽  
Shock Loss

A design trend evident in newly evolving aircraft turbine engines is a reduction in the aspect ratio of blading employed in fans, compressors, and turbines. As aspect ratio is reduced, various three-dimensional flow effects become significant which at higher aspect ratios could safely be neglected. This paper presents a new model for predicting the shock loss through a transonic or supersonic compressor blade row operating at peak efficiency. It differs from the classical Miller-Lewis-Hartmann normal shock model by taking into account the spanwise obliquity of the shock surface due to leading-edge sweep, blade twist, and solidity variation. The model is evaluated in combination with three test cases. Each was a low-aspect-ratio transonic stage which had exceeded its efficiency goals. Use of the revised shock loss model contributed 2.11 points to the efficiency of the first test case, 1.08 points to the efficiency of the second, and 1.38 points to the efficiency of the third.

Sign in / Sign up

Export Citation Format

Share Document