Measurement of Unsteady Flow Reattachment on an Airfoil with a Leading-Edge Horn-Ice Shape

2012 ◽  
Author(s):  
Phillip Ansell ◽  
Michael Bragg
Keyword(s):  
Unsteady Flow ◽  
Leading Edge ◽  
Flow Reattachment

Flow criticality governs leading-edge-vortex initiation on finite wings in unsteady flow

2021 ◽  
Vol 910 ◽  
Author(s):  
Yoshikazu Hirato ◽  
Minao Shen ◽  
Ashok Gopalarathnam ◽  
Jack R. Edwards
Keyword(s):  
Unsteady Flow ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex

Abstract

scholarly journals Unsteady Gapwise Periodicity of Oscillating Cascaded Airfoils

1982 ◽  
Author(s):  
F. O. Carta
Keyword(s):  
Unsteady Flow ◽  
Fourier Coefficient ◽  
Phase Angle ◽  
Leading Edge ◽  
Experimental Measurements ◽  
Pressure Data ◽  
Linear Cascade ◽  
Aerodynamic Damping ◽  
The Stability ◽  
Interblade Phase Angle

Tests were conducted on a linear cascade of airfoils oscillating in pitch to measure the unsteady pressure response on selected blades along the leading edge plane of the cascade and over the chord of the center blade. The pressure data were reduced to Fourier coefficient form for direct comparison, and were also processed to yield integrated loads and, particularly, the aerodynamic damping coefficient. In addition, results from two unsteady theories for cascaded blades with nonzero thickness and camber were compared with the experimental measurements. The three primary results that emerged from this investigation were: (a) from the leading edge plane blade data, the cascade was judged to be periodic in unsteady flow over the range of parameters tested, (b) as before, the interblade phase angle was found to be the single most important parameter affecting the stability of the oscillating cascade blades, and (c) the real blade theory and the experiment were in excellent agreement for the several cases chosen for comparison.

Initiation of Leading-Edge-Vortex Formation on Finite Wings in Unsteady Flow

2015 ◽  
Author(s):  
Yoshikazu Hirato ◽  
Minao Shen ◽  
Sachin Aggarwal ◽  
Ashok Gopalarathnam ◽  
Jack R. Edwards
Keyword(s):  
Unsteady Flow ◽  
Vortex Formation ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex

Investigation of Unsteady Flow Field in a Low-Speed One and a Half Stage Axial Compressor: Effects of Tip Gap Size on the Tip Clearance Flow Structure at Near Stall Operation

2014 ◽  
Author(s):  
Chunill Hah ◽  
Michael Hathaway ◽  
Joseph Katz
Keyword(s):  
Unsteady Flow ◽  
Flow Structure ◽  
Flow Instability ◽  
Axial Compressor ◽  
Leading Edge ◽  
Tip Clearance ◽  
Tip Clearance Flow ◽  
Low Speed ◽  
Clearance Flow ◽  
Tip Clearance Vortex

The primary focus of this paper is to investigate the effect of rotor tip gap size on how the rotor unsteady tip clearance flow structure changes in a low speed one and half stage axial compressor at near stall operation (for example, where maximum pressure rise is obtained). A Large Eddy Simulation (LES) is applied to calculate the unsteady flow field at this flow condition with both a small and a large tip gaps. The numerically obtained flow fields at the small clearance matches fairly well with the available initial measurements obtained at the Johns Hopkins University with 3-D unsteady PIV in an index-matched test facility which renders the compressor blades and casing optically transparent. With this setup, the unsteady velocity field in the entire flow domain, including the flow inside the tip gap, can be measured. The numerical results are also compared with previously published measurements in a low speed single stage compressor (Maerz et al. [2002]). The current study shows that, with the smaller rotor tip gap, the tip clearance vortex moves to the leading edge plane at near stall operating condition, creating a nearly circumferentially aligned vortex that persists around the entire rotor. On the other hand, with a large tip gap, the clearance vortex stays inside the blade passage at near stall operation. With the large tip gap, flow instability and related large pressure fluctuation at the leading edge are observed in this one and a half stage compressor. Detailed examination of the unsteady flow structure in this compressor stage reveals that the flow instability is due to shed vortices near the leading edge, and not due to a three-dimensional separation vortex originating from the suction side of the blade, which is commonly referred to during a spike-type stall inception. The entire tip clearance flow is highly unsteady. Many vortex structures in the tip clearance flow, including the sheet vortex system near the casing, interact with each other. The core tip clearance vortex, which is formed with the rotor tip gap flows near the leading edge, is also highly unsteady or intermittent due to pressure oscillations near the leading edge and varies from passage to passage. For the current compressor stage, the evidence does not seem to support that a classical vortex breakup occurs in any organized way, even with the large tip gap. Although wakes from the IGV influence the tip clearance flow in the rotor, the major characteristics of rotor tip clearance flows in isolated or single stage rotors are observed in this one and a half stage axial compressor.

Effects of the Clocking on the Internal Flow in a 1.5 Stage Axial Turbine

2006 ◽  
Author(s):  
Jongil Park ◽  
Minsuk Choi ◽  
Jehyun Baek
Keyword(s):  
Unsteady Flow ◽  
Relative Efficiency ◽  
Message Passing Interface ◽  
Flow Simulation ◽  
Internal Flow ◽  
Leading Edge ◽  
Maximum Efficiency ◽  
Axial Turbine ◽  
Flow Solver ◽  
Local Efficiency

A three-dimensional unsteady flow simulation is conducted to investigate clocking effects of a row of stators on the performance and internal flow in a 1.5 stage axial turbine. Although the original turbine has 22 blades of the first stator, 28 blades of the rotor and 28 blades of the second stator, the first stator is reduced by a factor of 22/28 to fit the blade ratio 1:1:1. The unsteady flow solver is implemented using the second order time marching and sliding mesh scheme between blade rows. And then, this flow solver is parallelized using MPI (Message Passing Interface) libraries to overcome the limitation of memories and to save the calculation time. Six relative positions of two rows of stators are investigated by positioning the second stator being clocked in a step of 1/6 pitch. The relative efficiency benefit of about 1% is obtained depending on clocking positions. At mid-span, the first stator wake is mixed up with the rotor wake before arriving at the leading edge of the second stator. The time-averaged local efficiency along the span at the maximum efficiency shows more uniform distribution than that at the minimum efficiency. Moreover, the variation of local efficiency at the mid-span does not coincide with that of overall efficiency. Therefore, it is found in this case that the only wake trajectory of the first stator is not a proper means of predicting the best and worst efficiency positions. This is why the relative efficiency benefit depending on the clocking position is obtained near the hub and casing in this study. So, it is necessary to find a general cause of the clocking effect which is applicable to every test case. The difference between maximum and minimum instantaneous efficiencies during one period is found to be smaller at the maximum efficiency than at the minimum efficiency.

Measurement of Unsteady Flow Reattachment on an Airfoil with an Ice Shape

AIAA Journal ◽  
2014 ◽  
Vol 52 (3) ◽  
pp. 656-659 ◽  
Author(s):  
Phillip J. Ansell ◽  
Michael B. Bragg
Keyword(s):  
Unsteady Flow ◽  
Flow Reattachment

scholarly journals Unsteady Flow Field due to Nozzle Wake Interaction With the Rotor in an Axial Flow Turbine: Part I — Rotor Passage Flow Field

1995 ◽  
Author(s):  
Michael A. Zaccaria ◽  
Budugur Lakshminarayana
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Axial Flow ◽  
Leading Edge ◽  
Turbine Rotor ◽  
Suction Surface ◽  
Pressure Surface ◽  
Aerodynamic Interaction ◽  
Flow Gradients ◽  
Rotor Flow

The flow field in turbine rotor passages is complex with unsteadiness caused by the aerodynamic interaction of the nozzle and rotor flow fields. The two-dimensional steady and unsteady flow field at midspan in an axial flow turbine rotor has been investigated experimentally using an LDV with emphasis on the interaction of the nozzle wake with the rotor flow field. The flow field in the rotor passage is presented in Part I, while the flow field downstream of the rotor is presented in Part II. Measurements were acquired at 37 axial locations from just upstream of the rotor to one chord downstream of the rotor. The time average flow field and the unsteadiness caused by the wake has been captured. As the nozzle wake travels through the rotor flow field, the nozzle wake becomes distorted with the region of the nozzle wake near the rotor suction surface moving faster than the region near the rotor pressure surface, resulting in a highly distorted wake. The wake is found to be spread out along the rotor pressure surface, as it convects downstream of midchord. The magnitude of the nozzle wake velocity defect grows until close to midchord, after which it decreases. High values of unresolved unsteadiness were observed at the rotor leading edge. This is due to the large flow gradients near the leading edge and the interaction of the nozzle wake with the rotor leading edge. High values of unresolved unsteadiness were also observed near the rotor pressure surface. This increase in unresolved unsteadiness is caused by the interaction of the nozzle wake with the flow near the rotor pressure surface.

Sign in / Sign up

Export Citation Format

Share Document