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 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 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 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.

scholarly journals Effects of Bulk Flow Pulsations on Film Cooling From Spanwise Oriented Holes

1998 ◽  
Author(s):  
I. S. Jung ◽  
J. S. Lee
Keyword(s):  
Film Cooling ◽  
Static Pressure ◽  
Free Stream ◽  
Free Stream Velocity ◽  
Bulk Flow ◽  
Stream Velocity ◽  
Pressure Pulsations ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Temperature Distributions

Experimental results are presented which describe the effect of bulk flow pulsations on film cooling from a single row of spanwise oriented holes. The film coolant is injected from the holes with 35 degree inclination angles and 90 degree orientation angles. Static pressure pulsations are produced by rotating vanes made of an array of six shutter blades, which are extended across the span of the exit of the wind tunnel test section. The free-stream velocity is in the form of near-sinusoidal variation and peak-to-peak amplitude is 11%. Changing two parameters which are time-averaged blowing ratio (M = 0.5, 1.0, 2.0) and frequency (f = 0, 36 Hz) gives the corresponding coolant Strouhal numbers in the range from 0 to 3.6. Time-averaged and phase-averaged temperature distributions are measured in spanwise/normal planes, and the adiabatic film cooling effectiveness is evaluated from the adiabatic wall temperature distributions. The results show that the imposed free-stream velocity pulsations generate static pressure difference variations between the plenum chamber and free-stream. These static pressure pulsations result in periodic variation of injectant flow rate and spanwise momentum which cause dramatic alterations in film coolant distributions, trajectories and corresponding adiabatic film cooling effectiveness distributions downstream of injection holes.

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