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  • 1
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    The structure and development of streamwise vortex arrays embedded in a turbulent boundary layer (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An investigation of the structure and development of streamwise vortices embedded in a turbulent boundary layer was conducted. The vortices were generated by a single spanwise row of rectangular vortex generator blades. A single embedded vortex was examined, as well as arrays of embedded counter rotating vortices produced by equally spaced vortex generators. Measurements of the secondary velocity field in the crossplane provided the basis for characterization of vortex structure. Vortex structure was characterized by four descriptors. The center of each vortex core was located at the spanwise and normal position of peak streamwise vorticity. Vortex concentration was characterized by the magnitude of the peak streamwise vorticity, and the vortex strength by its circulation. Measurements of the secondary velocity field were conducted at two crossplane locations to examine the streamwise development of the vortex arrays. Large initial spacings of the vortex generators produced pairs of strong vortices which tended to move away from the wall region while smaller spacings produced tight arrays of weak vortices close to the wall. A model of vortex interaction and development is constructed using the experimental results. The model is based on the structure of the Oseen Vortex. Vortex trajectories are modelled by including the convective effects of neighbors.
    Keywords: AERODYNAMICS
    Type: NASA-TM-105211 , E-6523 , NAS 1.15:105211
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    NASA TECHNICAL REPORTS
  • 2
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    The structure and development of streamwise vortex arrays embedded in a turbulent boundary layer (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The results of an experimental investigation of the structure and development of streamwise vortices embedded in a turbulent boundary layer are presented. Measurements of secondary velocity in the crossplane are used to characterize the vortex array structure. Measurements in the crossplane at two streamwise locations characterize the influence of interactions among the vortices on the array structure when the initial spacing between vortices is varied. Evidence of the merging of counter-rotating cores is found in embedded arrays of closely spaced vortices. A model of vortex interaction and development is constructed from the experimental results. This model is based on the structure of the two dimensional Ossen vortex. The decay of vortex circulation due to the merging of the cores is correlated with the crossplane gradient in streamwise vorticity occurring between an embedded vortex and its adjacent counter-rotating neighbors.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 92-0551
    Format: text
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  • 3
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    A new algorithm for five-hole probe calibration, data reduction, and uncertainty analysis (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A new algorithm for five-hole probe calibration and data reduction using a non-nulling method is developed. The significant features of the algorithm are: (1) two components of the unit vector in the flow direction replace pitch and yaw angles as flow direction variables; and (2) symmetry rules are developed that greatly simplify Taylor's series representations of the calibration data. In data reduction, four pressure coefficients allow total pressure, static pressure, and flow direction to be calculated directly. The new algorithm's simplicity permits an analytical treatment of the propagation of uncertainty in five-hole probe measurement. The objectives of the uncertainty analysis are to quantify uncertainty of five-hole results (e.g., total pressure, static pressure, and flow direction) and determine the dependence of the result uncertainty on the uncertainty of all underlying experimental and calibration measurands. This study outlines a general procedure that other researchers may use to determine five-hole probe result uncertainty and provides guidance to improve measurement technique. The new algorithm is applied to calibrate and reduce data from a rake of five-hole probes. Here, ten individual probes are mounted on a single probe shaft and used simultaneously. Use of this probe is made practical by the simplicity afforded by this algorithm.
    Keywords: AERODYNAMICS
    Type: NASA-TM-106458 , E-8319 , NAS 1.15:106458
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  • 4
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    The decay of longitudinal vortices shed from airfoil vortex generators (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An experimental study is conducted to examine the crossplane structure and streamwise decay of vortices shed from airfoil-type vortex generators. The vortex generators are set in a counter-rotating array spanning the full circumference of a straight pipe. The span of the vortex generators above the duct surface, h, is approximately equal to the local turbulent boundary layer thickness, delta. Measurement of three-component mean flow velocity in downstream crossplanes are used to characterize the structure of the shed vortices. Measurements in adjacent crossplanes (closely spaced along the streamwise coordinate) characterize the interaction and decay of the embedded vortices. A model constructed by the superposition of Oseen vortices is compared to the data for one test case.
    Keywords: AERODYNAMICS
    Type: NASA-CR-198356 , E-9730 , NAS 1.26:198356 , AIAA PAPER 95-1797 , Applied Aerodynamics Conference; Jun 19, 1995 - Jun 22, 1995; San Diego, CA; United States
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  • 5
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    Improving Diffusing S-duct Performance by Secondary Flow Control (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The objective of this research was to study ways to reduce inlet flow distortion (i.e., total pressure nonuniformity) and improve total pressure recovery in a diffusing S-duct. This was accomplished by controlling the development of secondary flows within the duct through the use of tapered-fin type vortex generators. Reported are results for the bare duct and seven different configurations of vortex generators. Data presented for each configuration include surface static pressure, surface flow visualization, and exit plane total pressure and transverse velocity. The performance of each configuration was assessed by calculating total pressure recovery and inlet distortion descriptors from the data and comparing them to the values for the bare duct. The best configuration tested reduced distortion (as measured by the DC(45) and DC(90) descriptors) by more than 50 percent while improving total pressure recovery by 0.5 percent. These results should provide valuable guidance in designing vortex generator installations in ducts and for assessing the accuracy of computational fluid dynamics (CFD) methods to calculate duct flows with installed vortex generators.
    Keywords: AERODYNAMICS
    Type: NASA-TM-106492 , E-8479 , NAS 1.15:106492 , AIAA PAPER 94-0365 , Aerospace Sciences Meeting and Exhibit; Jan 10, 1994 - Jan 13, 1994; Reno, NV; United States
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  • 6
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    An experimental investigation of S-duct flow control using arrays of low-profile vortex generators (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An experimental investigation was undertaken to measure the effect of various configurations of low-profile vortex generator arrays on the flow in a diffusing S-duct. Three parameters that characterize the vortex generator array were systematically varied to determine their effect: (1) the vortex generator height; (2) the streamwise location of the vortex generator array; and (3) the vortex generator spacing. Detailed measurements of total pressure at the duct exit, surface static pressure, and surface flow visualization were gathered for each vortex generator configuration. These results are reported here along with total pressure recovery and distortion coefficients determined from the experimental data. Each array of vortex generators tested improved total pressure recovery. The configuration employing the largest vortex generators was the most effective in reducing total pressure recovery. No configuration of vortex generators completely eliminated the flow separation that naturally occurs in the S-duct, however the extent of the separated flow region was reduced.
    Keywords: AERODYNAMICS
    Type: NASA-TM-106030 , E-7595 , NAS 1.15:106030 , Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States
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  • 7
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    Measurements and modeling of flow structure in the wake of a low profile wishbone vortex generator (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The results of an experimental examination of the vortex structures shed from a low profile 'wishbone' generator are presented. The vortex generator height relative to the turbulent boundary layer was varied by testing two differently sized models. Measurements of the mean three-dimensional velocity field were conducted in cross-stream planes downstream of the vortex generators. In all cases, a counter-rotating vortex pair was observed. Individual vortices were characterized by three descriptors derived from the velocity data; circulation, peak vorticity, and cross-stream location of peak vorticity. Measurements in the cross plane at two axial locations behind the smaller wishbone characterize the downstream development of the vortex pairs. A single region of stream wise velocity deficit is shared by both vortex cores. This is in contrast to conventional generators, where each core coincides with a region of velocity deficit. The measured cross-stream velocities for each case are compared to an Oseen model with matching descriptors. The best comparison occurs with the data from the larger wishbone.
    Keywords: AERODYNAMICS
    Type: NASA-TM-106468 , E-8334 , NAS 1.15:106468 , AIAA PAPER 94-0620 , Aerospace Sciences Meeting and Exhibit; Jan 10, 1994 - Jan 13, 1994; Reno, NV; United States
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