scholarly journals Aerodynamic Study of a NACA 64418 Rectangular Wing under Forced Pitching Motions

Fluids ◽  
2021 ◽  
Vol 6 (11) ◽  
pp. 394
Author(s):  
Dimitris Gkiolas ◽  
Dimitrios Mathioulakis
Keyword(s):  
Leading Edge ◽  
Suction Side ◽  
Damping Coefficient ◽  
Intermittent Flow ◽  
Pressure Transducers ◽  
Aerodynamic Damping ◽  
Subsonic Wind Tunnel ◽  
Parallel Tunnel ◽  
Edge Based ◽  
The Impact

The aerodynamic behavior of a pitching NACA 64418 rectangular wing was experimentally studied in a subsonic wind tunnel. The wing had a chord c = 0.5 m, a span which covered the distance between the two parallel tunnel walls and an axis of rotation 0.35 c far from the leading edge. Based on pressure distribution and flow visualization, intermittent flow separation (double stall) was revealed near the leading edge suction side when the wing was stationary, at angles higher than 17° and Re = 0.5 × 106. Under pitching oscillations, aerodynamic loads were calculated by integrating the output data of fast responding surface pressure transducers for various mean angles of attack (αm (max) = 15°), reduced frequencies (kmax = 0.2) and angle amplitudes Δα in the interval [2°, 8°]. The impact of the above parameters up to Re = 0.75 × 106 on the cycle-averaged lift and pitching moment loops is discussed and the cycle aerodynamic damping coefficient is calculated. Moreover, the boundaries of the above parameters are defined for the case that energy is transferred from the flow to the wing (negative aerodynamic damping coefficient), indicating the conditions under which aeroelastic instabilities are probable to occur.

On the Role of Leading-Edge Bumps in the Control of Stall Onset in Axial Fan Blades

2013 ◽  
Vol 135 (8) ◽  
Author(s):  
Alessandro Corsini ◽  
Giovanni Delibra ◽  
Anthony G. Sheard
Keyword(s):  
Numerical Study ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Leading Edge ◽  
Suction Side ◽  
Axial Fan ◽  
Early Recovery ◽  
Viscosity Models ◽  
Flow Mechanisms ◽  
The Impact

Taking a lead from the humpback whale flukes, characterized by a series of bumps that result in a sinusoidal-like leading edge, this paper reports on a three-dimensional numerical study of sinusoidal leading edges on cambered airfoil profiles. The turbulent flow around the cambered airfoil with the sinusoidal leading edge was computed at different angles of attack with the open source solver OpenFOAM, using two different eddy viscosity models integrated to the wall. The reported research focused on the effects of the modified leading edge in terms of lift-to-drag performance and the influence of camber on such parameters. For these reasons a comparison with a symmetric airfoil is provided. The research was primarily concerned with the elucidation of the fluid flow mechanisms induced by the bumps and the impact of those mechanisms on airfoil performance, on both symmetric and cambered profiles. The bumps on the leading edge influenced the aerodynamic performance of the airfoil, and the lift curves were found to feature an early recovery in post-stall for the symmetric profile with an additional gain in lift for the cambered profile. The bumps drove the fluid dynamic on the suction side of the airfoil, which in turn resulted in the capability to control the separation at the trailing edge in coincidence with the peak of the sinusoid at the leading edge.

scholarly journals Numerical Simulation on the Influence of Rotating Speed on the Hydraulic Loss Characteristics of Desalination Energy Recovery Turbine

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Bing Qi ◽  
Desheng Zhang ◽  
Qi Zhang ◽  
Mengcheng Wang ◽  
Ibra Fall
Keyword(s):  
Flow Separation ◽  
Energy Recovery ◽  
Internal Flow ◽  
Leading Edge ◽  
Suction Side ◽  
Radial Pressure ◽  
Hydraulic Loss ◽  
Rotating Speed ◽  
The Impact ◽  
Loss Mechanisms

The performance of energy recovery turbine (ERT) directly determines the cost and energy consumption of reverse osmosis desalination. In order to study the performance and loss mechanisms of ERT under different conditions, the external characteristics and the losses of different components were quantitatively analyzed. The loss mechanisms of each component in the turbine were revealed through the comparative analysis of the internal flow field. The results show that the efficiency is 2.2% higher than that at the design speed when turbine runs at n = 22000 r/min. The impeller losses account for more than 67% of the total losses. The impeller loss is mainly observed at the leading edge. The vortex on the pressure side of the leading edge is caused by the impact effect, while the vortex on the suction side of the leading edge is caused by the flow separation. With the increase in the rotating speed, the loss caused by flow separation in impeller decreases obviously. The volute loss is mainly observed near the tongue, which is caused by the flow separation at the tongue. The design of the tongue is very important to the performance of the volute. The turbulent kinetic energy (TKE) and loss decrease with the increase in the rotating speed. The loss in the draft tube is mainly observed at the inlet core. With the increase in the rotating speed, the turbulence pulsation and the radial pressure fluctuation amplitude reduce. Therefore, the turbine can be operated at the design or slightly higher than the design rotating speed under the condition that both the hydraulic condition and the intensity are satisfied, which are conducive to the efficient utilization of energy.

The Impact of Leakage Flow Tangential Velocity on Secondary Losses in a Shrouded Compressor Cascade

2012 ◽  
Author(s):  
J. W. Kim ◽  
J. S. Lee ◽  
S. J. Song ◽  
T. Kim ◽  
H-. W. Shin
Keyword(s):  
Secondary Flow ◽  
Tangential Velocity ◽  
Leading Edge ◽  
Suction Side ◽  
Leakage Flow ◽  
Compressor Cascade ◽  
Trailing Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex ◽  
The Impact

Experimental and numerical studies have been performed to investigate the effects of the leakage flow tangential velocity on the secondary flow and aerodynamic loss in an axial compressor cascade with a labyrinth seal. Six selected leakage flow tangential (vy/Uhub = 0.15, 0.25, 0.35, 0.45, 0.55 and 0.65) have been tested. In addition to the classical “secondary” flow, shroud trailing edge vortex and shroud leading edge vortex are examined. The overall loss decreases with increasing leakage flow tangential velocity. Increased leakage flow tangential velocity underturns the hub endwall flows through the blade passage, weakening the suction side hub corner separation. Due to the suction effect of the downstream cavity, increasing leakage flow tangential velocity weakens the shroud trailing edge vortex. Also, increasing leakage flow tangential velocity strengthens the shroud leading edge vortex, weakening the pressure side leg of the horseshoe vortex, and, in turn, the passage vortex. Thus, the overall loss is reduced with increasing leakage flow tangential velocity.

Fracture Analysis of a First Stage Turbine Blade

2010 ◽  
Author(s):  
Reza Ghorbani ◽  
Saeed Asadikouhanjani ◽  
Karsten Kusterer ◽  
Anis Haj Ayed
Keyword(s):  
Crack Propagation ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Service Failure ◽  
Leading Edge ◽  
Suction Side ◽  
Turbine Engines ◽  
Nickel Base Superalloy ◽  
Premature Failure ◽  
The Impact

Blade failures in gas turbine engines often lead to the loss of all downstream stages and it can have a dramatic effect on the availability of the turbine engines. This paper presents the analysis of an in service failure of a first stage gas turbine blade. The premature failure of the blade, made of nickel-base superalloy Inconel 738 LC, occurred after a service life of 8,127 EOH with normal start/stop and caused extensive damage to the unit. Crack growth mechanism has been evaluated based on macroscopic and microscopic observations of the fracture surfaces. Chemical analyses were carried out to identify the possible causes of the failures by examining anomalies in the chemical composition and microstructure analysis through SEM observations. The analysis of the different regions of fracture surface shows that crack propagation is mainly related to fatigue mechanism. Typical fatigue striations could be identified under a homogeneous oxide layer. The crack propagation occurred in the pressure-suction side direction and the initial crack origin is located on the missing part near leading edge area. The impact marks on the first stage leading edge of the blade and the general damage of the turbine give indication that the crack initiation was caused by an impact of a broken piece from first stage vanes or another object of unknown source.

Quantitative CFD Analyses of Particle Deposition on a Subsonic Axial Compressor Blade

2015 ◽  
Author(s):  
Alessio Suman ◽  
Rainer Kurz ◽  
Nicola Aldi ◽  
Mirko Morini ◽  
Klaus Brun ◽  
...  
Keyword(s):  
Particle Deposition ◽  
Fluid Dynamic ◽  
Axial Compressor ◽  
Leading Edge ◽  
Suction Side ◽  
Sticking Probability ◽  
Particle Impact ◽  
Kinematic Characteristics ◽  
The Impact ◽  
Dynamic Phenomena

In literature there are some studies related to the fouling phenomena in transonic compressors, but, in industrial applications (heavy-duty compressor, pump stations, etc.) the subsonic compressors are widespread. It is of great interest to the manufacturer to discover the fouling phenomenon related to this type of compressor. This paper presents three-dimensional numerical simulations of the micro-particle ingestion on a subsonic axial compressor rotor carried out by means of a commercial computational fluid dynamic code. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separate from the continuous phase. The number of particles, sizes, and concentrations are specified in order to perform a quantitative analysis of the particle impact on the blade surface. In this paper the particle impact pattern and the kinematic characteristics (velocity and angle) of the impact are shown. Both of the blade zones affected by particle impact and the blade zones affected by particle deposition are analyzed. The particle deposition is established by using the quantity called sticking probability. The sticking probability links the kinematic characteristics of particle impact on the blade with fouling phenomenon. The results show that micro-particles tend to follow the flow by impacting at full span with a higher impact concentration on the leading edge. The suction side is affected only close to the leading edge and, at the hub, close to the trailing edge. Particular fluid-dynamic phenomena such as separation, stagnation and tip leakage vortex strongly influence the impact location of the particles. The kinematic analysis showed a high tendency of particle adhesion on the suction side, especially for smaller particles for which the fluid dynamic phenomena play a key role regarding particle impact velocity and angle.

Aerothermal Investigations of Mixing Flow Phenomena in Case of Radially Inclined Ejection Holes at the Leading Edge

1999 ◽  
Vol 122 (2) ◽  
pp. 334-339 ◽  
Author(s):  
Dieter E. Bohn ◽  
Karsten A. Kusterer
Keyword(s):  
Secondary Flow ◽  
Gas Turbines ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Leading Edge ◽  
Suction Side ◽  
Back Side ◽  
Stagnation Line ◽  
Flow Phenomena ◽  
The Impact

A leading edge cooling configuration is investigated numerically by application of a three-dimensional conjugate fluid flow and heat transfer solver, CHT-flow. The code has been developed at the Institute of Steam and Gas Turbines, Aachen University of Technology. It works on the basis of an implicit finite volume method combined with a multiblock technique. The cooling configuration is an axial turbine blade cascade with leading edge ejection through two rows of cooling holes. The rows are located in the vicinity of the stagnation line, one row on the suction side, the other row is on the pressure side. The cooling holes have a radial ejection angle of 45 deg. This configuration has been investigated experimentally by other authors and the results have been documented as a test case for numerical calculations of ejection flow phenomena. The numerical investigations focus on the aerothermal mixing process in the cooling jets and the impact on the temperature distribution on the blade surface. The radial ejection angles lead to a fully three-dimensional and asymmetric jet flow field. Within a secondary flow analysis, the cooling fluid jets are investigated in detail. The secondary flow fields include asymmetric kidney vortex systems with one dominating vortex on the back side of the jets. The numerical and experimental data show a respectable agreement concerning the vortex development. [S0889-504X(00)00102-1]

Impact of Tip Clearance Size and Rotation Speed on the Surge Onset in a High Pressure Centrifugal Compressor

2012 ◽  
Author(s):  
Nicolas Buffaz ◽  
Isabelle Trébinjac
Keyword(s):  
Centrifugal Compressor ◽  
Rotation Speed ◽  
Pressure Sensors ◽  
Leading Edge ◽  
Suction Side ◽  
Boundary Layer Separation ◽  
Tip Clearance ◽  
Vaned Diffuser ◽  
The Impact ◽  
Blade Leading Edge

The results presented in the paper aim at investigating the impact of tip clearance size and rotation speed on the surge onset in a transonic single-stage centrifugal compressor composed of a backswept splittered unshrouded impeller and a vaned diffuser. For that purpose, various slow throttle ramps into surge were conducted from 100% to 60% design speed of the compressor and two different tip clearance heights were investigated. The 1MW LMFA-ECL test rig was used to carry out the tests in the compressor stage. Unsteady pressure measurements up to 150 KHz were carried out in the inducer (i.e. the entry zone of the impeller between the main blade leading edge and the splitter blade leading edge) and in the diffuser thanks to nine and fifteen static pressure sensors respectively. At cruise rotation speed (92.7% of the nominal rotation speed), the surge is triggered by a boundary layer separation on the diffuser vane suction side whatever the tip clearance height may be. No precursor of surge or pre-surge activity has been recorded in the diffuser or in the impeller. The surge reveals a spike-type inception and the tip clearance increase does not change the path into instability. At lower rotation speeds high frequency disturbances (nearly half the BPF) have been recorded in the inducer before surge. These disturbances can be understood as “tip clearance rotating disturbances” because they are generated at the leading edge of the main blades and move along the tip clearance trajectory. These disturbances reveal a very unstable behavior while the compressor runs into a stable operating point even if the flow at the tip of impeller is dramatically affected by these disturbances. But these disturbances do not trigger the surge which always originates in the diffuser.

scholarly journals Shock Characteristics Measured Upstream of Both a Forward-Swept and an Aft-Swept Fan

2007 ◽  
Author(s):  
Gary G. Podboy ◽  
Martin J. Krupar ◽  
Daniel L. Sutliff ◽  
Csaba Horvath
Keyword(s):  
Flow Visualization ◽  
Leading Edge ◽  
Suction Side ◽  
Surface Flow ◽  
Rotor Blades ◽  
Laser Doppler Velocimeter ◽  
Pressure Measurements ◽  
Pressure Transducers ◽  
Unsteady Pressure ◽  
Unsteady Pressure Measurements

Three different types of diagnostic data — blade surface flow visualization, shroud unsteady pressure, and laser Doppler velocimeter (LDV) — were obtained on two fans, one forward-swept and one aft-swept, in order to learn more about the shocks which propagate upstream of these rotors when they are operated at transonic tip speeds. Flow visualization data are presented for the forward-swept fan operating at 13831 RPMc and for the aft-swept fan operating at 12500 and 13831 RPMc (corresponding to tip rotational Mach numbers of 1.07 and 1.19, respectively). The flow visualization data identify where the shocks occur on the suction side of the rotor blades. These data show that at the takeoff speed, 13831 RPMc, the shocks occurring in the tip region of the forward-swept fan are further downstream in the blade passage than with the aft-swept fan. Shroud unsteady pressure measurements were acquired using a linear array of 15 equally-spaced pressure transducers extending from two tip axial chords upstream to 0.8 tip axial chords downstream of the static position of the tip leading edge of each rotor. Such data are presented for each fan operating at one subsonic and five transonic tip speeds. The unsteady pressure data show relatively strong detached shocks propagating upstream of the aft-swept rotor at the three lowest transonic tip speeds, and weak, oblique pressure disturbances attached to the tip of the aft-swept fan at the two highest transonic tip speeds. The unsteady pressure measurements made with the forward-swept fan do not show strong shocks propagating upstream of that rotor at any of the tested speeds. A comparison of the forward-swept and aft-swept shroud unsteady pressure measurements indicates that at any given transonic speed the pressure disturbance just upstream of the tip of the forward-swept fan is much weaker than that of the aft-swept fan. The LDV data suggest that at 12500 and 13831 RPMc, the forward-swept fan swallowed the passage shocks occurring in the tip region of the blades, whereas the aft-swept fan did not. Due to this difference, the flows just upstream of the two fans were found to be quite different at both of these transonic speeds. Nevertheless, despite distinct differences just upstream of the two rotors, the two fan flows were much more alike about one axial blade chord further upstream. As a result, the LDV data suggest that it is unwise to attempt to determine the effect that the shocks have on far field noise by focusing only on measurements (or CFD predictions) made very near the rotor. Instead, these data suggest that it is important to track the shocks throughout the inlet.

scholarly journals Experimental investigation of Mini Gurney Flaps in combination with vortex generators for improved wind turbine blade performance

2021 ◽  
Author(s):  
Jörg Alber ◽  
Marinos Manolesos ◽  
Guido Weinzierl-Dlugosch ◽  
Johannes Fischer ◽  
Alexander Schönmeier ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Wind Turbine ◽  
Leading Edge ◽  
Suction Side ◽  
Rotor Blades ◽  
Force Balance ◽  
Vortex Generators ◽  
Gurney Flaps ◽  
First Case ◽  
The Impact

Abstract. This wind tunnel study investigates the aerodynamic effects of Mini Gurney flaps (MGFs) and their combination with vortex generators (VGs) on the performance of airfoils and wind turbine rotor blades. VGs are installed on the suction side aiming at stall delay and increased maximum lift. MGFs are thin angle profiles that are attached at the trailing edge in order to increase lift at pre-stall operation. The implementation of both these passive flow control devices is accompanied by a certain drag penalty. The wind tunnel tests are conducted at the Hermann- Föttinger Institut of the Technische Universität Berlin. Lift is determined with a force balance and drag with a wake rake for static angles of attack from −5° to 17° at a constant Reynolds number of 1.5 million. The impact of different MGF heights including 0.25 %, 0.5 % and 1.0 % and an uniform VG height of 1.1 % of the chord length are tested on three airfoils that are characteristic for different sections of large rotor blades. Furthermore, the clean and the tripped baseline cases are considered. In the latter, leading edge transition is forced by means of Zig Zag (ZZ) turbulator tape. The preferred configurations are the smallest MGF on the NACA63(3)618 and the AH93W174 (mid to tip blade region) and the medium sized MGF combined with VGs on the DU97W300 (root to mid region). Next, the experimental lift and drag polar data is imported into the software QBlade in order to design a generic rotor blade. The blade performance is simulated with and without the add-ons based on two case studies. In the first case, the retrofit application on an existing blade mitigates the adverse effects of the ZZ tape. Stall is delayed and the aerodynamic efficiency is partly recovered leading to an improvement of the power curve. In the second case, the new design application allows for the design of a more slender blade while maintaining the power output. Moreover, the alternative blade appears to be more resistant against forced leading edge transition.

Stall Flutter Measurements on a Rectangular Wing

2018 ◽  
Author(s):  
D. Gkiolas ◽  
F. Mouzakis ◽  
D. S. Mathioulakis
Keyword(s):  
Center Of Mass ◽  
Leading Edge ◽  
Stream Velocity ◽  
Flow Conditions ◽  
Rotating Shaft ◽  
Pressure Transducers ◽  
Subsonic Wind Tunnel ◽  
Aspect Ratios ◽  
Spring System ◽  
Stall Flutter

The continuous development of wind turbine technology gradually leads to larger, more flexible blades with increasing aspect ratios and high tip speeds, while in everyday operation or extreme cases the blades experience stalled flow conditions. These aforementioned facts create the need for further study and physical understanding of stall induced vibrations – stall flutter. In this context an aeroelastic setup was constructed at the NTUA subsonic wind tunnel with a rigid rectangular wing (500 mm × 1400 mm) of a NACA 64-418 airfoil supported by a spring system that enables pitching and plunging motions. The elastic axis of the wing is located 35% of the chord far from the leading edge while its center of mass at 46%. Increasing the free stream velocity (up to Re = 670 000) under various initial static angles of attack, the wing was set at fluid induced oscillations (pitching and plunging). The response of the wing under these conditions was recorded employing two accelerometers and two wire sensors for both the rotational and linear wing displacements. At the same time, in the middle of the wing span thirty (30) fast responsive pressure transducers measured the pressure distribution along the chord, while strain gauges attached to the wing rotating shaft measured the applied unsteady aerodynamic loading. Based on the above simultaneously measured quantities various aspects of the aeroelastic instability of the examined wing were revealed.

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