Interactions between embedded vortices and injectant from film cooling holes with compound angle orientations in a turbulent boundary layer

Experimental results are presented that describe the effects of embedded, longitudinal vortices on heat transfer and film injectant downstream of two staggered rows of film cooling holes with compound angle orientations. Holes are oriented so that their angles with respect to the test surface are 30 deg in a spanwise/normal plan projection, and 35 deg in a streamwise/normal projection. A blowing ratio of 0.5, nondimensional injection temperature parameter [theta] of about 1.5, and free-stream velocity of 10 m/s are employed. Injection hole diameter is 0.945 cm to give a ratio of vortex core diameter to hole diameter of 1.6--1.67 just downstream of the injection holes (x/d = 10.2). At the same location, vortex circulation magnitudes range from 0.15 m[sup 2]/s to 0.18 m[sup 2]/s. By changing the sign of the angle of attack of the half-delta wings used to generate the vortices, vortices are produced that rotate either clockwise or counterclockwise when viewed looking downstream in spanwise/normal planes. The most important conclusion is that local heat transfer and injectant distributions are strongly affected by the longitudinal embedded vortices, including their directions of rotation and their spanwise positions with respect to film injection holes. Differences resulting from vortex rotation are due to secondary flow vectors, especially beneath vortex cores, which are in different directions with respect to the spanwise velocity components of injectant after it exits the holes. Surveys of streamwise mean velocity, secondary flow vectors, total pressure, and streamwise mean vorticity are also presented that further substantiate these findings.Non

Effects of an Embedded Vortex on Injectant from a Single Film-Cooling Hole in a Turbulent Boundary Layer

Effects of embedded longitudinal vortices on heat transfer in turbulent boundary layers with injection from a single film cooling hole are described. These results were obtained at a freestream velocity of 10 m/s, with a film cooling hole inclined 30 degrees to horizontal and a blowing ratio of about 0.50. The ratio of vortex core diameter to injection hole diameter was 2.14, and the ratio of circulation to injection velocity times hole diameter was about 2.8. Coolant distributions and spatially resolved heat transfer measurements indicate that injection hole centerlines must be a least 2.0–2.5 vortex core diameters away from the vortex center in the lateral direction to avoid significant alterations to wall heat transfer and distributions of film coolant. Under these circumstances, protection from film cooling is evident at least up to 55 hole diameters downstream of injection. When the injection hole is closer to the vortex center, secondary flows convect most injectant into the vortex upwash and thermal protection from film cooling is destroyed for streamwise locations from the injection hole greater than 17.5 hole diameters.NPS Research FoundationAero-Propulsion Laboratory MIPR Number FY 1455-88-N0608

Spatial resolution and measurement of turbulence in the viscous sublayer using subminiature hot-wire probes

Measurements in the viscous sublayer of a flat-plate turbulent boundary layer in air, using single hot-wire sensors with lengths from 1-60 viscous length scales show that, at a given distance from the surface, the turbulence intensity, flatness factor, and skewness factor of the longitudinal velocity fluctuation are nearly independent of wire length when the latter is less than 20-25 times the viscous length scale (i.e. 20-25 "wall units"), and decrease significantly and abruptly for larger wire lengths. This conclusion is consistent with other workers' probability density functions of streak spacing: the lateral spacing of "streaks" in the viscous sublayer is 80-100wall units on average with minimum spacing of 20-25 wall units, which implies that signals would be strongly attenuated by wires whose length exceeds 20-25 wall units. To achieve wire lengths of less than 20-25 wall units, subminiature hot wire probes like those described by Ligrani and Bradshaw (1987), having lengths as small as 150 ~tm, are necessary for sublayer measurements in typical laboratory wind tunnels. As well as the measurements mentioned above, dissipation spectra are presented, to show the effect of spanwise averaging on the high-frequency motions, which is necessarily more severe than the effect on overall intensities

Spatial resolution and downwash velocity corrections for multiple-hole pressure probes in complex flows

Methods to account for finite spatial resolution and induced downwash velocity are given for multiple-hole pressure probes as they are used to measure complex three-dimensional flow fields. Spatial resolution limitations result because pressures from different ports are not measured at the same physical location. As transverse gradients increase in magnitude, uncorrected errors then become larger. Because of this, most existing correction techniques employ schemes which depend on gradients of velocity or pressure (Ikui and Inoue 1970; Sitaram et al. 1981; Eibeck and Eaton 1985; Westphal etal. 1987). A simpler and more sensible approach for a five-hole probe corrects pressures so that all appear to be measured at the location of the central hole by accounting for the exact spacing between different pressure ports...This work was sponsored by the US Army Office of Aviation Research and Development, NASA-Defense Purchase Request No. C-80019-F. Dr. K. Civinskas was the program monitor

Spatial resolution and downwash velocity corrections for multiple-hole pressure probes in complex flows

The article of record as published may be found at http://dx.doi.org/10.1007/BF00193427Correction schemes for finite spatial resolution and induced downwash velocity are presented which have application to the measurement of complex three-dimensional flow fields using five-hole angle-type pressure probes. In the study, induced downwash velocity is assumed to be proportional to the transverse gradients of streamwise velocity. The present correction schemes are validated by application to flows including vortices embedded within turbulent boundary layers and flows in a curved channel with 1.27-cm width, a 40-to-1 aspect ratio, and 59.7 cm of convex surface curvature.NASA ORDER C-80019-FApproved for public release; distribution is unlimited

Film cooling from spanwise-oriented holes in two staggered rows

The article of record as published may be found at http://dx.doi.org/101115/1.2841158ASME 1995 International Gas Turbine and Aeroengine Congress and Exposition Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration Houston, Texas, USA, June 5–8, 1995 Conference Sponsors: International Gas Turbine InstituteAdiabatic effectiveness and iso-energetic heat transfer coefficients are presented from measurements downstream of film-cooling holes inclined at 30 deg. With respect to the test surface in spanwise/normal planes. With this configuration, holes are spaced 3d apart in the spanwise direction and 4d in the streamwise direction in two staggered rows. Results are presented for an injectant to free-stream density ratio near 1.0, and injection blowing ratios from 0.5 to 1.5. Spanwise-averaged adiabatic effectiveness values downstream of the spanwise/normal plane holes are significantly higher than values measured downstream of simple angle holes for x/d < 25--70 (depending on blowing ratio) when compared for the same normalized streamwise location, blowing ratio, and spanwise and streamwise hole spacings. Spanwise-averaged iso-energetic Stanton number ratios range between 1.0 and 1.41, increase with blowing ratio at each streamwise station, and show little variation with streamwise location for each value of blowing ratio tested.USDO

Film cooling from a single row of holes oriented in spanwise/normal planes

Experimental results are presented that describe the development and structure of flow downstream of a single row of film-cooling holes inclined at 30 deg from the test surface in spanwise/normal planes. With this configuration, holes are spaced 6d apart in the spanwise direction in a single row. Results are presented for a ratio of injectant density to free-stream density near 1.0, and injection blowing ratios from 0.5 to 1.5. Compared to results measured downstream of simple angle (streamwise) oriented holes, spanwise-averaged adiabatic effectiveness values are significantly higher for the same spanwise hole spacing, normalized streamwise location x/d, and blowing ratio m when m = 1.0 and 1.5 for x/d < 80. The injectant from the spanwise/normal holes is also less likely to lift off of the test surface than injectant from simple angle holes. This is because lateral components of momentum keep higher concentrations of injectant in closer proximity to the surface. As a result, local adiabatic effectiveness values show significantly greater spanwise variations and higher local maxima at locations immediately downstream of the holes. Spanwise-averaged iso-energetic Stanton number ratios range between 1.07 and 1.26, which are significantly higher than values measured downstream of two other injection configurations (one of which is simple angle, streamwise holes) when compared at the same x/d and blowing ratio