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.

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.

Measurements in a Turbulent Boundary Layer Over a d-Type Surface Roughness

1975 ◽  
Vol 42 (3) ◽  
pp. 591-597 ◽  
Author(s):  
D. H. Wood ◽  
R. A. Antonia
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Turbulent Boundary Layer ◽  
Turbulent Energy ◽  
Shear Stresses ◽  
Normal Velocity ◽  
Mean Velocity ◽  
Outer Flow ◽  
Intensity Measurements ◽  
Normal And Shear Stresses

Mean velocity and turbulence intensity measurements have been made in a fully developed turbulent boundary layer over a d-type surface roughness. This roughness is characterised by regular two-dimensional elements of square cross section placed one element width apart, with the cavity flow between elements being essentially isolated from the outer flow. The measurements show that this boundary layer closely satisfies the requirement of exact self-preservation. Distribution across the layer of Reynolds normal and shear stresses are closely similar to those found over a smooth surface except for the region immediately above the grooves. This similarity extends to distributions of third and fourth-order moments of longitudinal and normal velocity fluctuations and also to the distribution of turbulent energy dissipation. The present results are compared with those obtained for a k-type or sand grained roughness.

Conditional Sampling in a Transitional Boundary Layer Under High Freestream Turbulence Conditions

2003 ◽  
Vol 125 (1) ◽  
pp. 28-37 ◽  
Author(s):  
Ralph J. Volino ◽  
Michael P. Schultz ◽  
Christopher M. Pratt
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Streamwise Velocity ◽  
Turbulent Shear ◽  
Conditional Sampling ◽  
Freestream Turbulence ◽  
Mean Velocity ◽  
Transitional Boundary Layer ◽  
Turbulent Shear Stress ◽  
Order Of Magnitude

Conditional sampling has been performed on data from a transitional boundary layer subject to high (initially 9%) freestream turbulence and strong (K=ν/U∞2dU∞/dx as high as 9×10−6) acceleration. Methods for separating the turbulent and nonturbulent zone data based on the instantaneous streamwise velocity and the turbulent shear stress were tested and found to agree. Mean velocity profiles were clearly different in the turbulent and nonturbulent zones, and skin friction coefficients were as much as 70% higher in the turbulent zone. The streamwise fluctuating velocity, in contrast, was only about 10% higher in the turbulent zone. Turbulent shear stress differed by an order of magnitude, and eddy viscosity was three to four times higher in the turbulent zone. Eddy transport in the nonturbulent zone was still significant, however, and the nonturbulent zone did not behave like a laminar boundary layer. Within each of the two zones there was considerable self-similarity from the beginning to the end of transition. This may prove useful for future modeling efforts.

scholarly journals Active control of multiscale features in wall-bounded turbulence

2019 ◽  
Vol 36 (1) ◽  
pp. 12-21 ◽  
Author(s):  
Xiaotong Cui ◽  
Nan Jiang ◽  
Xiaobo Zheng ◽  
Zhanqi Tang
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulent Energy ◽  
Streamwise Velocity ◽  
Discrete Wavelet ◽  
Wall Region ◽  
Mean Velocity ◽  
Pzt Actuator ◽  
The Impact ◽  
Near Wall

Abstract This study experimentally investigates the impact of a single piezoelectric (PZT) actuator on a turbulent boundary layer from a statistical viewpoint. The working conditions of the actuator include a range of frequencies and amplitudes. The streamwise velocity signals in the turbulent boundary layer flow are measured downstream of the actuator using a hot-wire anemometer. The mean velocity profiles and other basic parameters are reported. Spectra results obtained by discrete wavelet decomposition indicate that the PZT vibration primarily influences the near-wall region. The turbulent intensities at different scales suggest that the actuator redistributes the near-wall turbulent energy. The skewness and flatness distributions show that the actuator effectively alters the sweep events and reduces intermittency at smaller scales. Moreover, under the impact of the PZT actuator, the symmetry of vibration scales’ velocity signals is promoted and the structural composition appears in an orderly manner. Probability distribution function results indicate that perturbation causes the fluctuations in vibration scales and smaller scales with high intensity and low intermittency. Based on the flatness factor, the bursting process is also detected. The vibrations reduce the relative intensities of the burst events, indicating that the streamwise vortices in the buffer layer experience direct interference due to the PZT control.

Interaction between a spatially growing turbulent boundary layer and embedded streamwise vortices

1996 ◽  
Vol 326 ◽  
pp. 151-179 ◽  
Author(s):  
Junhui Liu ◽  
Ugo Piomelli ◽  
Philippe R. Spalart
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Turbulent Boundary Layer ◽  
Turbulent Kinetic Energy ◽  
Vortex Core ◽  
Eddy Viscosity ◽  
Shear Stresses ◽  
Streamwise Vortices ◽  
Mean Velocity ◽  
Production Term

The interaction between a zero-pressure-gradient turbulent boundary layer and a pair of strong, common-flow-down, streamwise vortices with a sizeable velocity deficit is studied by large-eddy simulation. The subgrid-scale stresses are modelled by a localized dynamic eddy-viscosity model. The results agree well with experimental data. The vortices drastically distort the boundary layer, and produce large spanwise variations of the skin friction. The Reynolds stresses are highly three-dimensional. High levels of kinetic energy are found both in the upwash region and in the vortex core. The two secondary shear stresses are significant in the vortex region, with magnitudes comparable to the primary one. Turbulent transport from the immediate upwash region is partly responsible for the high levels of turbulent kinetic energy in the vortex core; its effect on the primary stress 〈u′v′〉 is less significant. The mean velocity gradients play an important role in the generation of 〈u′v′〉 in all regions, while they are negligible in the generation of turbulent kinetic energy in the vortex core. The pressure-strain correlations are generally of opposite sign to the production terms except in the vortex core, where they have the same sign as the production term in the budget of 〈u′v′〉. The results highlight the limitations of the eddy-viscosity assumption (in a Reynolds-averaged context) for flows of this type, as well as the excessive diffusion predicted by typical turbulence models.

Three-Dimensional Flow Near the Blade/Endwall Junction of a Gas Turbine: Application of a Boundary Layer Fence

1991 ◽  
Author(s):  
J. T. Chung ◽  
T. W. Simon ◽  
J. Buddhavarapu
Keyword(s):  
Boundary Layer ◽  
Gas Turbine ◽  
Film Cooling ◽  
Three Dimensional ◽  
Horseshoe Vortex ◽  
Management Technique ◽  
Suction Surface ◽  
Cooling Flow ◽  
Passage Vortex ◽  
Cooling Function

A flow management technique designed to reduce some harmful effects of secondary flow in the endwall region of a turbine passage is introduced. A boundary layer fence in the gas turbine passage is shown to improve the likelihood of efficient film cooling on the suction surface near the endwall. The fence prevents the pressure side leg of the horseshoe vortex from crossing to the suction surface and impinging on the wall. The vortex is weakened and decreased in size after being deflected by the fence. Such diversion of the vortex will prevent it from removing the film cooling flow allowing the flow to perform its cooling function. Flow visualization on the suction surface and through the passage shows the behavior of the passage vortex with and without the fence. Laser Doppler velocimetry is employed to quantify these observations.

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