PIV Measurements of Flow-Field Downstream of a Cylinder in Uniform Flow and Comparisons With CFD

2013 ◽  
Author(s):  
Peter B. Stetson ◽  
Spyros A. Kinnas
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Uniform Flow ◽  
Hydrodynamic Coefficients ◽  
Two Dimensional ◽  
General Sense ◽  
Piv Measurements ◽  
Functional Approximation ◽  
Cfd Models ◽  
Stream Direction

This paper examines the ability of two-dimensional CFD models to predict flow downstream of a cylinder in uniform flow. PIV measurements of the flow-field downstream of the cylinder in uniform flow are first presented. “Slices” of the flow at several locations along the cylinder are compared to show the variation of the flow in the cross-stream direction. Then the PIV flow is compared with RANS and LES simulations of the flow. Hydrodynamic coefficients and velocities are compared. In a general sense, two-dimensional CFD can give a functional approximation of the unsteady flow field downstream of the cylinder.

Two-Dimensional Experimental Investigation on the Effects of a Fowler Flap Gap and Overlap Size on the Wake Flow Field

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
David Demel ◽  
Mohsen Ferchichi ◽  
William D. E. Allan ◽  
Marouen Dghim
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Angle Of Attack ◽  
Wake Flow ◽  
Two Dimensional ◽  
Edge Region ◽  
Suction Surface ◽  
Trailing Edge ◽  
Piv Measurements ◽  
Image Velocimetry

This work details an experimental investigation on the effects of the variation of flap gap and overlap sizes on the flow field in the wake of a wing-section equipped with a trailing edge Fowler flap. The airfoil was based on the NACA 0014-1.10 40/1.051 profile, and the flap was deployed with 40 deg deflection angle. Two-dimensional (2D) particle image velocimetry (PIV) measurements of the flow field in the vicinity of the main wing trailing edge and the flap region were performed for the optimal flap gap and overlap, as well as for flap gap and overlap increases of 2% and 4% chord beyond optimal, at angles of attack of 0 deg, 10 deg, and 12 deg. For all the configurations investigated, the flow over the flap was found to be fully stalled. At zero angle of attack, increasing the flap gap size was found to have minor effects on the flow field but increased flap overlap resulted in misalignment between the main wing boundary layer (BL) flow and the slot flow that forced the flow in the trailing edge region of the main wing to separate. When the angle of attack was increased to near stall conditions (at angle of attack of 12 deg), increasing the flap gap was found to energize and improve the flow in the trailing edge region of the main wing, whereas increased flap overlap further promoted flow separation on the main wing suction surface possibly steering the wing into stall.

Characteristics of Tip Clearance Flow Instability in a Transonic Compressor

2010 ◽  
Author(s):  
Chunill Hah ◽  
Melanie Voges ◽  
Martin Mueller ◽  
Heinz-Peter Schiffer
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Flow Instability ◽  
Tip Clearance ◽  
Piv Measurements ◽  
Tip Clearance Flow ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Clearance Flow ◽  
Tip Clearance Vortex

In the present study, unsteady flow phenomena due to tip clearance flow instability in a modern transonic axial compressor rotor are studied in detail. First, unsteady flow characteristics due the oscillating tip clearance vortex measured with the particle image velocimetry (PIV) and casing-mounted unsteady pressure transducers are analyzed and compared to numerical results with a large eddy simulation (LES). Then, measured characteristic frequencies of the unsteady flow near stall operation are investigated. The overall purpose of the study is to advance the current understanding of the unsteady flow field near the blade tip in an axial transonic compressor rotor near the stall operating condition. Flow interaction between the tip leakage vortex and the passage shock is inherently unsteady in a transonic compressor. The currently applied PIV measurements indicate that the flow near the tip region is unsteady even at the design condition. This self-induced unsteadiness increases significantly as the compressor operates toward the stall condition. PIV data show that the tip clearance vortex oscillates substantially near stall. The calculated unsteady characteristics from LES agree well with the PIV measurements. Calculated unsteady flow fields show that the formation of the tip clearance vortex is intermittent and the concept of vortex breakdown from steady flow analysis does not seem to apply in the current flow field. Fluid with low momentum near the pressure side of the blade close to the leading edge periodically spills over into the adjacent blade passage. The spectral analysis of measured end wall and blade surface pressure shows that there are two dominant frequencies near stall. One frequency is about 40–60% of the rotor rotation and the other dominant frequency is about 40–60% of the blade passing frequency (BPF). The first frequency represents the movement of a large blockage over several consecutive blade passages against the rotor rotation. The second frequency represents traditional tip flow instability, which has been widely observed in subsonic compressors. The LES simulations show that the second frequency is due to movement of the instability vortex.

Cumulative nonlinear distortion of an acoustic wave propagating through non-uniform flow

1977 ◽  
Vol 83 (4) ◽  
pp. 751-773 ◽  
Author(s):  
M. Kurosaka
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Near Field ◽  
Direct Consequence ◽  
Confluent Hypergeometric Function ◽  
Uniform Flow ◽  
The Body ◽  
Form Representation ◽  
Physical Features ◽  
Special Case

In this paper we examine how the unsteady flow field radiated from an oscillating body is altered from the result of acoustic theory as the direct consequence of disturbances propagating through the non-uniform flow produced by the presence of the body. Taking the specific example of an oscillating airfoil placed in supersonic flow and having the contour of a parabolic arc, we derive a closed-form representation for the unsteady flow field in terms of the confluent hypergeometric function. The analytical expression reveals explicitly that, though the body shape has a negligible effect in the near field, it inextricably affects the unsteady flow at a large distance, both in its amplitude and phase, and substantially modifies the results of acoustic theory. In addition, we display the relation of this solution to the ‘fundamental solution’ and the other salient physical features connected with disturbances propagating through non-uniform flow. The present results recover Whitham's rule in the limit of zero frequency of oscillation and also include, as another special case, the unsteady solution for a wedge obtained by Carrier and Van Dyke.

Ultrasonic Measurement of Instantaneous Velocity Vector Profile

2007 ◽  
Author(s):  
Yasushi Takeda ◽  
Yuji Tasaka
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Temporal Variation ◽  
Velocity Vector ◽  
Focal Point ◽  
Instantaneous Velocity ◽  
Effective Diameter ◽  
Dimensional System ◽  
Two Dimensional ◽  
Instantaneous Velocity Vector

This paper proposes a new technique that enables the measurement of an instantaneous velocity vector profile in multi-dimensions on a line of the flow field. A system to achieve this goal was developed based on ultrasonic velocity profiling (UVP) by using multiple transducers. A focusing transducer, which reduces the effective diameter of ultrasonic beams around the focal point, was used to minimize the spatial uncertainty in the measurement. A two-dimensional system was constructed by using a normal transducer as a receiver and a focusing transducer as both an emitter and a receiver, and successfully applied to an actual flow field, rigid body motion of fluid in a rotating cylinder, for two-dimensional velocity vector measurements. To estimate the influence of existence of an intermediate wall, acoustic field under the developed system was computed by solving two-dimensional wave equation and then the focal point of an ultrasonic beam was determined to optimize the system. The system was applied to measure two dimensional velocity components of a periodic velocity fluctuation in a wake of a cylinder in a shallow channel as an example of unsteady flow. Obtained temporal variation of velocity vector profile confirmed an applicability of the developed system to unsteady flow. The vortex shedding in the wake was well reproduced as in the vorticity distribution, which was computed from the temporal variation of the vector field using Taylor frozen hypothesis. Although a temporal resolution is still not high, we conclude that applicability of the measurement system has been confirmed.

Time-Accurate Euler Simulation of Interaction of Nozzle Wake and Secondary Flow With Rotor Blade in an Axial Turbine Stage Using Nonreflecting Boundary Conditions

1996 ◽  
Vol 118 (4) ◽  
pp. 663-678 ◽  
Author(s):  
S. Fan ◽  
B. Lakshminarayana
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
Unsteady Flow ◽  
Secondary Flow ◽  
Rotor Blade ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Turbine Stage ◽  
Unsteady Pressure ◽  
Nonreflecting Boundary Conditions

The objective of this paper is to investigate the three-dimensional unsteady flow interactions in a turbomachine stage. A three-dimensional time-accurate Euler code has been developed using an explicit four-stage Runge–Kutta scheme. Three-dimensional unsteady nonreflecting boundary conditions are formulated at the inlet and the outlet of the computational domain to remove the spurious numerical reflections. The three-dimensional code is first validated for two-dimensional and three-dimensional cascades with harmonic vortical inlet distortions. The effectiveness of the nonreflecting boundary conditions is demonstrated. The unsteady Euler solver is then used to simulate the propagation of nozzle wake and secondary flow through the rotor and the resulting unsteady pressure field in an axial turbine stage. The three-dimensional and time-dependent propagation of nozzle wakes in the rotor blade row and the effects of nozzle secondary flow on the rotor unsteady surface pressure and passage flow field are studied. It was found that the unsteady flow field in the rotor is highly three dimensional and the nozzle secondary flow has significant contribution to the unsteady pressure on the blade surfaces. Even though the steady flow at the midspan is nearly two dimensional, the unsteady flow is three dimensional and the unsteady pressure distribution cannot be predicted by a two-dimensional analysis.

A Flux-Split Solution Procedure for Unsteady Inlet Flow Calculations

1992 ◽  
Vol 114 (2) ◽  
pp. 198-204 ◽  
Author(s):  
H. S. Pordal ◽  
P. K. Khosla ◽  
S. G. Rubin
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Unsteady Flow ◽  
Sparse Matrix ◽  
Strong Shock ◽  
Solution Procedure ◽  
Navier Stokes ◽  
Time Varying ◽  
Two Dimensional ◽  
Boundary Layer Interaction

The solution of the reduced Navier Stokes (RNS) equations is considered using a flux-split procedure. Unsteady flow in a two dimensional engine inlet is computed. The problems of unstart and restart are investigated. A sparse matrix direct solver combined with a domain decomposition strategy is used to compute the unsteady flow field. Strong shock-boundary layer interaction, time varying shocks, and time varying recirculation regions are efficiently captured.

The correction of wind tunnel nozzles for two-dimensional, supersonic flow

1950 ◽  
Vol 2 (3) ◽  
pp. 195-208 ◽  
Author(s):  
R. E. Meyer ◽  
M. Holt
Keyword(s):  
Wind Tunnel ◽  
Uniform Flow ◽  
Pressure Measurements ◽  
Two Dimensional ◽  
Simple Test ◽  
Perfect Gas ◽  
Isentropic Flow ◽  
Two Dimensional Flow ◽  
Stream Direction ◽  
Flow Stream

SummaryThe paper is concerned with the two-dimensional, steady, irrotational, isentropic flow of a perfect gas in a wind tunnel nozzle which is found to produce a flow in the test rhombus deviating slightly from the desired uniform flow.The minimum corrections are derived that must be applied to the liners in order to produce a uniform flow in the test rhombus. If the uncorrected nozzle produces a flow of uniform direction, measurement of the pressure on the axis, in the test rhombus, suffices to determine these corrections (Section 5). If not, further pressure measurements are required (Section 6). A simple test is indicated for checking whether the flow stream direction is uniform (Section 6).The method cannot be used to correct for deviations from a two-dimensional flow.

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