Effects of Bulk Flow Pulsations on Phase-Averaged and Time-Averaged Film-Cooled Boundary Layer Flow Structure

2001 ◽  
Vol 123 (3) ◽  
pp. 559-566 ◽  
Author(s):  
I.-S. Jung ◽  
P. M. Ligrani ◽  
J. S. Lee
Keyword(s):  
Boundary Layer ◽  
Flow Structure ◽  
Static Pressure ◽  
Flow Characteristics ◽  
Streamwise Velocity ◽  
Phase Shifts ◽  
Bulk Flow ◽  
Pulsation Period ◽  
Pulsation Frequency ◽  
Flow Pulsations

Flow structure in boundary layers film cooled from a single row of round, simple angle holes, and subject to bulk flow pulsations, is investigated, including phase-averaged streamwise velocity variations, and alterations of time-averaged flow structure. The bulk flow pulsations are in the form of sinusoidal variations of velocity and static pressure, and are similar to flow variations produced by potential flow interactions and passing shock waves near turbine surfaces in gas turbine engines. Injection hole length to diameter ratio is 1.6, time-averaged blowing ratio is 0.50, and bulk flow pulsation frequencies range from 0–32 Hz, which gives modified Strouhal numbers from 0–1.02. Profiles of time-averaged flow characteristics and phase-averaged flow characteristics, measured in the spanwise/normal plane at x/d=5 and z/d=0, show that effects of pulsations are larger as imposed pulsation frequency goes up, with the most significant and dramatic changes at a frequency of 32 Hz. Phase shifts of static pressure (and streamwise velocity) waveforms at different boundary layer locations from the wall are especially important. As imposed pulsation frequency varies, this includes changes to the portion of each pulsation phase when the largest influences of static pressure waveform phase-shifting occur. At a frequency of 32 Hz, these phase shifts result in higher instantaneous injectant trajectories, and relatively higher injectant momentum levels throughout a majority of each pulsation period.

scholarly journals Bulk Flow Pulsations and Film Cooling: Flow Structure Just Downstream of the Holes

1995 ◽  
Author(s):  
Phillip M. Ligrani ◽  
J. Michael Cuthrell ◽  
Ruoming Gong
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Static Pressure ◽  
Streamwise Velocity ◽  
Bulk Flow ◽  
Shear Stresses ◽  
Pressure Pulsations ◽  
Mean Velocity ◽  
Cooling Flow ◽  
Flow Pulsations

Experimental results are presented which describe the effects of bulk flow pulsations on film cooling from a single row of simple angle film cooling holes. The pulsations are in the form of sinusoidal variations of static pressure and streamwise velocity. Such pulsations are important in turbine studies because: (i) static pressure pulsations result in significant periodic variations of film cooling flow rates, coverage, and trajectories, and (ii) static pressure pulsations occur near blade surfaces in operating engines from potential flow interactions between moving blade rows and from families of passing shock waves. Distributions of ensemble-averaged and time-averaged Reynolds stress tensor components are investigated at x / d=4.5 along with distributions of all three mean velocity components, where x is streamwise distance from the downstream edge of the holes and d is hole diameter. Important changes are evident in all measured quantities which must be accounted for in any closure model used to simulate unsteadiness from the relative motion of two adjacent blade rows. In particular, maximum Reynolds shear stresses −2u′v′¯/u∞¯2 are lower in regions containing the largest film concentrations because the strong shear layer produced by the injectant is more three-dimensional, larger in extent, and oscillates its position from the wall with time. The pulsations also produce significant changes to profiles of u′w′¯/u∞¯2, u′2¯/u∞¯2, v′2¯/u∞¯2, and w′2¯/u∞¯2 in the film cooled boundary layer, and increase u¯/u∞¯ over most of the boundary layer thickness at spanwise locations near the holes.

scholarly journals Bulk Flow Pulsations and Film Cooling: Flow Structure Just Downstream of the Holes

1997 ◽  
Vol 119 (3) ◽  
pp. 568-573 ◽  
Author(s):  
P. M. Ligrani ◽  
R. Gong ◽  
J. M. Cuthrell
Keyword(s):  
Film Cooling ◽  
Static Pressure ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Bulk Flow ◽  
Shear Stresses ◽  
Pressure Pulsations ◽  
Mean Velocity ◽  
Cooling Flow ◽  
Flow Pulsations

Experimental results are presented that describe the effects of bulk flow pulsations on film cooling from a single row of simple angle film cooling holes. The pulsations are in the form of sinusoidal variations of static pressure and streamwise velocity. Such pulsations are important in turbine studies because: (i) Static pressure pulsations result in significant periodic variations of film cooling flow rates, coverage, and trajectories, and (ii) static pressure pulsations occur near blade surfaces in operating engines from potential flow interactions between moving blade rows and from families of passing shock waves. Distributions of ensemble-averaged and time-averaged Reynolds stress tensor components are investigated just downstream of the holes along with distributions of all three mean velocity components. Important changes are evident in all measured quantities. In particular, maximum Reynolds shear stresses −2u′υ′/u∞2 are lower in regions containing the largest film concentrations because the strong shear layer produced by the injectant is more three dimensional, larger in extent, and oscillates its position from the wall with time.

Effects of Bulk Flow Pulsations on Film-Cooled Boundary Layer Structure

1997 ◽  
Vol 119 (1) ◽  
pp. 56-66 ◽  
Author(s):  
P. M. Ligrani ◽  
R. Gong ◽  
J. M. Cuthrell ◽  
J. S. Lee
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Film Cooling ◽  
Static Pressure ◽  
Layer Structure ◽  
Bulk Flow ◽  
Shear Stresses ◽  
Pressure Pulsations ◽  
Boundary Layer Structure ◽  
Flow Pulsations

Experimental results are presented which describe the effects of bulk flow pulsations on film cooled boundary layer structure. The film is produced by a single row of simple angle film cooling holes and the pulsations are in the form of sinusoidal variations of static pressure and streamwise velocity. Such pulsations are important in turbine studies because: (i) static pressure pulsations result in significant periodic variations of film cooling flow rates, coverage, and trajectories, and (ii) static pressure pulsations occur near blade surfaces in operating engines from passing shock waves and potential flow interactions between moving blade rows. Distributions of ensemble-averaged and time-averaged Reynolds stress tensor components are presented for x/d of 4.5, 9.8, 16.4, and 24.1 along with distributions of streamwise mean velocity and streamwise mean vorticity, where x is streamwise distance from the downstream edge of the holes and d is hole diameter. Important changes from the imposed bulk flow pulsations are evident in all measured quantities, especially just downstream of the holes at x/d = 4.5. Here, Maximum Reynolds shear stresses −2u′v′/u∞2 are reduced by the pulsations in regions containing the largest film concentrations. This is because the shear layer produced by the injectant oscillates its position as each pulsations is imposed. This causes the shear layer to become more diffused as it is spread over a larger spatial volume.

scholarly journals Effects of Bulk Flow Pulsations on Film Cooling From Different Length Injection Holes at Different Blowing Ratios

1998 ◽  
Author(s):  
H. J. Seo ◽  
J. S. Lee ◽  
P. M. Ligrani
Keyword(s):  
Film Cooling ◽  
Bulk Flow ◽  
Turbine Engines ◽  
Pulsation Frequency ◽  
Gas Turbine Engines ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Temperature Distributions ◽  
Flow Interactions ◽  
Flow Pulsations

Bulk flow pulsations in the form of sinusoidal variations of velocity and static pressure at injectant Strouhal numbers from 0.8 to 10.0 are investigated as they affect film cooling from a single row of simple angle holes. Similar flow variations are produced by potential flow interactions and passing shock waves near turbine surfaces in gas turbine engines. Time-averaged temperature distributions, phase-averaged temperature distributions, adiabatic film cooling effectiveness values, and iso-energetic Stanton numbers show that important alterations to film cooling protection occur as pulsation frequency, coolant Strouhal number, blowing ratio, and non-dimensional injection hole length are changed. Overall, the pulsations affect film performance end behavior more significantly both as L/D decreases, and as blowing ratio decreases.

scholarly journals The Effect of Bulk Flow Pulsations on Film Cooling From Two Rows of Holes

1997 ◽  
Author(s):  
Dong Kee Sohn ◽  
Joon Sik Lee
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Free Stream ◽  
Bulk Flow ◽  
Phase Lag ◽  
Cooling Effectiveness ◽  
Freestream Velocity ◽  
Film Cooling Effectiveness ◽  
Temperature Distributions ◽  
Flow Pulsations

Effect of bulk flow pulsations on film cooling from two rows of holes with inline and staggered arrangements is experimentally investigated. As a baseline study, a single row injection is also tested. Two-row injection is important because the phase lag between the two rows may cause changes in the film coolant coverage. Potential flow pulsations are generated by the rotating shutter mechanism attached downstream of the test section. Free-stream Strouhal number based on the boundary layer thickness is in the range of 0.033–0.33, and the amplitude of the phase-averaged freestream velocity due to static pressure variation about 10–20% Both the time-averaged and phase-averaged temperature distributions in the cross-sectional plane of the boundary layer are presented for four different pulsation frequencies of 0, 4, 20 and 40 Hz. Film cooling effectiveness is evaluated from the adiabatic wall temperature distributions, with time-averaged temperature measurements showing rapid diffusion of the injectant due to the free-stream pulsations. Effect of the phase lag between two rows is evidenced from the phase-averaged measurements, particularly in the case of staggered hole arrangement. All film cooling effectiveness distributions are reduced compared to no-pulsation case. Effect of pulsations appears dominantly in the case of the two-row staggered arrangement which shows more than 35% reduction in the film cooling effectiveness.

Effects of Bulk Flow Pulsations on Film Cooling From Different Length Injection Holes at Different Blowing Ratios

1999 ◽  
Vol 121 (3) ◽  
pp. 542-550 ◽  
Author(s):  
H. J. Seo ◽  
J. S. Lee ◽  
P. M. Ligrani
Keyword(s):  
Film Cooling ◽  
Bulk Flow ◽  
Turbine Engines ◽  
Pulsation Frequency ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Temperature Distributions ◽  
Flow Interactions ◽  
Flow Pulsations ◽  
And Behavior

Bulk flow pulsations in the form of sinusoidal variations of velocity and static pressure at injectant Strouhal numbers from 0.8 to 10.0 are investigated as they affect film cooling from a single row of simple angle holes. Similar flow variations are produced by potential flow interactions and passing shock waves near turbine surfaces in gas turbine engines. Time-averaged temperature distributions, phase-averaged temperature distributions, adiabatic film cooling effectiveness values, and iso-energetic Stanton numbers show that important alterations to film cooling protection occur as pulsation frequency, coolant Strouhal number, blowing ratio, and nondimensional injection hole length are changed. Overall, the pulsations affect film performance and behavior more significantly both as L/D decreases, and as blowing ratio decreases.

scholarly journals Characteristics of Helium Gas with High Temperature and High Pressure Flowing through a 90-Degree Elbow

2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
Beibei Feng ◽  
Yanfei Sun ◽  
Xingtuan Yang ◽  
Shengqiang Li ◽  
Jiyuan Tu ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Static Pressure ◽  
Flow Characteristics ◽  
Boundary Layer Separation ◽  
Separation Process ◽  
Centrifugal Forces ◽  
Helium Flow ◽  
Primary Loop ◽  
Helium Gas ◽  
Simulation Results

There exists a certain 90° elbow structures in the helium circulation of HTGR-10. In terms of energy-saving and design simplification of reactor’s primary loop, 90° elbow can be used to measure the helium flow and the content of water vapor, both of which are significant in an accident. It is necessary to make an in-depth research of the flow characteristics of helium flowing 90° elbow. Simulation results indicate that fluid’s motion in the elbow is under the control of the centrifugal forces. Static pressure near the extrados is higher than that near the intrados. Boundary layer separation occurs at the latter half intrados of the elbow. The vortex emerges during the separation process and increases the energy dissipation. Velocity in the near-intrados region is higher than that in the near-extrados region, which is opposite to the pressure distribution trend. Under the action of the centrifugal forces, the secondary flow emerges in the latter half of the elbow and complicates the flow field by generating two vortexes which rotate in a different direction.

Flow Characteristics Within and Downstream of a Double-Row Array of Shallow Spherical and Cylindrical Dimples

2006 ◽  
Author(s):  
Artem Khalatov ◽  
Aaron Byerley
Keyword(s):  
Reynolds Number ◽  
Unsteady Flow ◽  
Flow Structure ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Bulk Flow ◽  
Experimental Program ◽  
Double Row ◽  
Motion Feature ◽  
Flow Fluctuations

The experimental program was performed in the U.S. Air Force Academy water tunnel to visualize details of the unsteady flow structure in front of, within and downstream of a double-row array of shallow (h/D = 0.1) spherical and cylindrical dimples placed on a flat plate. The dimple projected diameter was 50.8 mm. The center of the first array was located at 88,0 mm downstream of the elliptically-shaped leading edge of the plate, the spanwise dimple pitch is 76.2 mm (Sz/D = 1.50). The second array was arranged in a staggered mode with the same spanwise pitch and the axial pitch between rows of 88.0 mm (Sx/D = 1.73). The diameter-based Reynolds number ReD ranged from 3,260 to 23,450, while the length-based Reynolds number Rex in front of the first array varied from 4,010 to 28,840. The laminar flow existed upstream of the first array for all flow conditions studied. In front of the second array the flow structure appeared to have either laminar or turbulent depending on the Reynolds number and streamline location. Flow visualizations were performed at 13 different flow speeds using the dye visualization technique. All recordings were made with a SONY-DCR VX2000 video camera. Adobe Premiere 6.5 software was used to analyze the flow characteristics using the slow motion feature. The results presented include details of the unsteady flow structure, bulk flow fluctuations and laminar-turbulent flow transition. The upstream vortex structures reduce bulk flow fluctuations beyond the second array making them smaller than those after the first array. At ReD > 13,000 the spherical dimples in the second array produce more significant bulk flow fluctuations than cylindrical dimples.

scholarly journals Neutrally stable wave motions in thermally stratified Poiseuille-Couette flow

1998 ◽  
Vol 40 (1) ◽  
pp. 123-144 ◽  
Author(s):  
James P. Denier ◽  
Andrew P. Bassom
Keyword(s):  
Boundary Layer ◽  
Couette Flow ◽  
Flow Structure ◽  
Maximum Velocity ◽  
Streamwise Velocity ◽  
Asymptotic Structure ◽  
Thermal Buoyancy ◽  
Maximum Value ◽  
Limiting Behaviour ◽  
Wave Modes

AbstractThe influence of thermal buoyancy on neutral wave modes in Poiseuille-Couette flow is considered. We examine the modifications to the asymptotic structure first described by Mureithi, Denier & Stott [16], who demonstrated that neutral wave modes in a strongly thermally stratified boundary layer are localized at the position where the streamwise velocity attains its maximum value. The present work demonstrates that such a flow structure also holds for Poiseuille-Couette flow but that a new flow structure emerges as the position of maximum velocity approaches the wall (and which occurs as the level of shear, present as a consequence of the Couette component of the flow, is increased). The limiting behaviour of these wave modes is discussed thereby allowing us to identify the parameter regime appropriate to the eventual restabilization of the flow at moderate levels of shear.

Flow Characteristics Within and Downstream of a Single Shallow Cylindrical and Spherical Dimple: Effect of Pre-Dimple Boundary Layer Thickness

2005 ◽  
Author(s):  
Artem Khalatov ◽  
Aaron Byerley ◽  
Robert Vincent
Keyword(s):  
Boundary Layer ◽  
Unsteady Flow ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Bulk Flow ◽  
Flow Structures ◽  
Flow Speeds ◽  
Flow Oscillations

The objective of this study is to investigate the details of the average and unsteady flow structures in front, inside and after shallow (h/D = 0.1) spherical and cylindrical dimples placed on a flat plate at the different distances with different pre-dimple boundary layer thicknesses. The dimple projected (surface) diameter was 50.8 mm with the dimple centers located at 88 mm and 264 mm downstream of the elliptical leading edge of the flat plate. Experimental program was established in the U.S. Air Force Academy water tunnel, both dimple configurations were tested across the range of freestream water velocities from 0.07 to 0.52 m/s corresponding with diameter based Reynolds numbers ReD ranging from 3,200 to 23,500. The length based Reynolds number Rex ranged from 3,940 to 110,450 while the non-dimensional boundary layer thickness δ0/h ranged from 0.28 to 1.18. The inlet flow turbulence was below 1% at all flow speeds. Laminar flow existed upstream of the dimple for all of the flow conditions studied. Flow visualizations were performed inside and downstream of each dimple at 10 to 13 different flow speeds. All recordings were made with a SONY-DCR VX2000 video camera. Five different colors of dye were injected through five cylindrical ports, 1.0 mm in diameter, positioned at locations upstream and inside the dimples. Adobe Premiere 6.5 software was used to analyze the flow characteristics using the slow motion feature. LDV measurements were made both in front of and downstream of the dimple. The results presented include the vortex patterns, in-dimple separation zone extent, unsteady flow phenomena (bulk flow oscillations), velocity profiles after the dimple, and some features of the laminar-turbulent flow transition downstream of a single cylindrical dimple. The data obtained revealed three-dimensional and unsteady flow structures inside and downstream of the dimples, the important role of the pre-dimple boundary layer thickness. Increasing the δ0/h ratio reduces the downstream bulk flow oscillations at very low Reynolds numbers. However, at ReD>16,500 for the cylindrical dimple and at ReD>24,000 for the spherical dimple the boundary layer thickness had little effect on the bulk flow oscillations. A comparison of both spherical and cylindrical dimple geometric configurations was made to assess their relative benefits.

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