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  • 1
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    NLINEAR - NONLINEAR CURVE FITTING PROGRAM (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A common method for fitting data is a least-squares fit. In the least-squares method, a user-specified fitting function is utilized in such a way as to minimize the sum of the squares of distances between the data points and the fitting curve. The Nonlinear Curve Fitting Program, NLINEAR, is an interactive curve fitting routine based on a description of the quadratic expansion of the chi-squared statistic. NLINEAR utilizes a nonlinear optimization algorithm that calculates the best statistically weighted values of the parameters of the fitting function and the chi-square that is to be minimized. The inputs to the program are the mathematical form of the fitting function and the initial values of the parameters to be estimated. This approach provides the user with statistical information such as goodness of fit and estimated values of parameters that produce the highest degree of correlation between the experimental data and the mathematical model. In the mathematical formulation of the algorithm, the Taylor expansion of chi-square is first introduced, and justification for retaining only the first term are presented. From the expansion, a set of n simultaneous linear equations are derived, which are solved by matrix algebra. To achieve convergence, the algorithm requires meaningful initial estimates for the parameters of the fitting function. NLINEAR is written in Fortran 77 for execution on a CDC Cyber 750 under NOS 2.3. It has a central memory requirement of 5K 60 bit words. Optionally, graphical output of the fitting function can be plotted. Tektronix PLOT-10 routines are required for graphics. NLINEAR was developed in 1987.
    Keywords: STATISTICS AND PROBABILITY
    Type: LAR-13934
    Format: text
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  • 2
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    A parametric experimental study of the slotted-wall boundary condition (1978)
    In:  CASI
    Details
    Publication Date: 2006-02-22
    Description: An experimental study of slotted upper and lower walls in a two dimensional transonic wind tunnel with solid sidewalls is reported. Results are presented for several slot spacings and slot openness ratios. The experimental data were pressure measurements which were made on an airfoil model and on a sidewall near one of the slotted walls. The slotted-wall boundary condition coefficient, which related the pressure and streamline curvature near the wall, was determined from the wall pressure measurements. The measured wall-induced interference was correlated with the experimental values for the boundary condition coefficient. This correlation was compared with theory.
    Keywords: AERODYNAMICS
    Type: Advanced Technol. Airfoil Res., Vol. 1, Pt. 2; p 459-471
    Format: text
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  • 3
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    Design and calibration of slotted walls for transonic airfoil wind tunnels (1979)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The traditional procedure for estimating the performance of slotted walls for airfoil wind tunnels is reviewed, and a modification which improves the accuracy of this procedure is described. Unlike the traditional procedure, the modified procedure indicates that the design of airfoil wind-tunnel walls which induce minimal blockage and streamline-curvature effects is feasible. The design and testing of such a slotted wall is described. It is shown experimentally that the presence of a model can affect the plenum pressure and thus make the use of the plenum pressure as a calibration reference questionable. Finally, an ONERA experiment which shows the effect of the sidewall boundary layer on the measured model normal force is discussed.
    Keywords: AERODYNAMICS
    Type: Advanced Technol. Airfoil Res., Vol. 1, Pt. 1; p 433-443
    Format: application/pdf
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  • 4
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    A detailed experimental study of the flow in the vicinity of the slotted wall of a wind tunnel with applications to the homogeneous slotted-wall boundary condition (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The results of an experimental study of the flow in the vicinity of the slotted wall of a transonic wind tunnel are presented. A general description of the test setup and the wall configurations studied are given as are examples of the pressure data measured on the airfoil and the walls of the tunnel. The flow angles measured in the vicinity of the slot are examined with implications as to their use in the theory of homogeneous slotted walls. Preliminary values of the classical, homogeneous, slotted-wall boundary-condition coefficient are given and compared with theory.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 86-0749
    Format: text
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  • 5
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    FLEXWAL: A computer program for predicting the wall modifications for two-dimensional, solid, adaptive-wall tunnels (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A program called FLEXWAL for calculating wall modifications for solid, adaptive-wall wind tunnels is presented. The method used is the iterative technique of NASA TP-2081 and is applicable to subsonic and transonic test conditions. The program usage, program listing, and a sample case are given.
    Keywords: AERODYNAMICS
    Type: NASA-TM-84648 , NAS 1.15:84648
    Format: application/pdf
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  • 6
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    Potential flow through a cascade of alternately displaced circular bodies: The rod-wall wind tunnel boundary conditions (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The classic slotted-wall boundary-condition coefficient for rod-wall wind tunnels is derived by approximating the potential flow solution through a cascade of two staggered rows of rods. A comparison with the corrected Chen and Mears solution for flow through an unstaggered cascade is made.
    Keywords: AERODYNAMICS
    Type: NASA-TM-85750 , L-15617 , NAS 1.15:85750
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  • 7
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    A parametric experimental study of the interference effects and the boundary-condition coefficient of slotted wind-tunnel walls (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: An experimental study of slotted upper and lower walls in a two-dimensional transonic wind tunnel with solid sidewalls is reported. Results are presented for several slot spacings and slot openness ratios. The experimental data are pressure measurements which were made on an airfoil model and on a sidewall near one of the slotted walls. The slotted-wall boundary-condition coefficient, which relates the pressure and streamline curvature near the wall, is determined from the wall pressure measurements. The measured wall-induced interference is correlated with the experimental values for the boundary-condition coefficient. This correlation is compared with theory.
    Keywords: RESEARCH AND SUPPORT FACILITIES (AIR)
    Type: AIAA PAPER 78-805 , Aerodynamic Testing Conference; Apr 19, 1978 - Apr 21, 1978; San Diego, CA
    Format: text
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  • 8
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    A method for modifying two-dimensional adaptive wind-tunnel walls including analytical and experimental verification (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The theoretical development of a simple and consistent method for removing the interference in adaptive-wall wind tunnels is reported. A Cauchy integral formulation of the velocities in an imaginary infinite extension of the real wind-tunnel flow is obtained and evaluated on a closed contour dividing the real and imaginary flow. The contour consists of the upper and lower effective wind-tunnel walls (wall plus boundary-layer displacement thickness) and upstream and downstream boundaries perpendicular to the axial tunnel flow. The resulting integral expressions for the streamwise and normal perturbation velocities on the contour are integrated by assuming a linear variation of the velocities between data-measurement stations along the contour. In an iterative process, the velocity components calculated on the upper and lower boundaries are then used to correct the shape of the wall to remove the interference. Convergence of the technique is shown numerically for the cases of a circular cylinder and a lifting and nonlifting NACA 0012 airfoil in incompressible flow. Experimental convergence at a transonic Mach number is demonstrated by using an NACA 0012 airfoil at zero lift.
    Keywords: RESEARCH AND SUPPORT FACILITIES (AIR)
    Type: NASA-TP-2081 , L-15491 , NAS 1.60:2081
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  • 9
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    Predicting Wall Modifications for Adaptive Wind Tunnels (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Wall shape changed iteratively until it matches streamlines. FLEXWAL predicts upper and lower wall modifications necessary to remove wall-interference effects in adaptive-wall wind tunnels. FLEXWAL aids in elimination of wall-interference effects on objects tested in typical two-dimensional wind tunnel with rigid sidewalls and flexible, solid floor and ceiling boundaries. Iterative procedure valid for subsonic and transonic test conditions, and convergence of method verified both analytically and experimentally. FLEXWAL written in FORTRAN IV for batch execution.
    Keywords: MACHINERY
    Type: LAR-13301 , NASA Tech Briefs (ISSN 0145-319X); 10; 2; P. 106
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  • 10
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    Application of Pressure-Based Wall Correction Methods to Two NASA Langley Wind Tunnels (2001)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper is a description and status report on the implementation and application of the WICS wall interference method to the National Transonic Facility (NTF) and the 14 x 22-ft subsonic wind tunnel at the NASA Langley Research Center. The method calculates free-air corrections to the measured parameters and aerodynamic coefficients for full span and semispan models when the tunnels are in the solid-wall configuration. From a data quality point of view, these corrections remove predictable bias errors in the measurement due to the presence of the tunnel walls. At the NTF, the method is operational in the off-line and on-line modes, with three tests already computed for wall corrections. At the 14 x 22-ft tunnel, initial implementation has been done based on a test on a full span wing. This facility is currently scheduled for an upgrade to its wall pressure measurement system. With the addition of new wall orifices and other instrumentation upgrades, a significant improvement in the wall correction accuracy is expected.
    Keywords: Research and Support Facilities (Air)
    Type: AIAA Paper 2001-2472 , 19th AIAA Applied Aerodynamics Conference; Jun 11, 2001 - Jun 14, 2001; Anaheim, CA; United States
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