Laser schlieren crossed-beam measurements in a supersonic jet shear layer
01 Nov 1970-AIAA Journal (American Institute of Aeronautics and Astronautics (AIAA))-Vol. 8, Iss: 11, pp 2074-2075
About: This article is published in AIAA Journal.The article was published on 1970-11-01. It has received 14 citations till now. The article focuses on the topics: Schlieren photography & Synthetic schlieren.
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22 Aug 2014
TL;DR: In this paper, a focusing laser differential interferometer (FLDI) was used to measure refractive signals from transition and turbulence in a high-speed wind tunnel and to characterize the effect of freestream disturbances and their effect on laminar boundary layer transition.
Abstract: Characterization of freestream disturbances and their effect on laminar boundary layer transition is of great importance in high-speed wind tunnel testing, where significant differences between the behavior of scale-model and free-flight transition have long been noted. However, the methods traditionally used to perform this characterization in low-speed flows present significant difficulties when applied to supersonic and especially hypersonic wind tunnels. The design and theory of a focusing laser differential interferometer (FLDI) instrument, originally invented by Smeets at the Institut Saint-Louis in the 1970s and used recently by Parziale in the CalTech T5 shock tunnel, is presented. It is a relatively-simple, non-imaging common-path interferometer for measuring refractive signals from transition and turbulence, and it has a unique ability to look through facility windows, ignore sidewall boundary-layers and vibration, and concentrate only on the refractive signal near a pair of sharp beam foci in the core flow. The instrument’s low cost and ease of implementation make it a promising alternative to traditional hot-wire anemometry and particle-based methods for turbulence characterization. Benchtop experiments using a turbulent supersonic air jet demonstrate its focusing ability, frequency response, unwanted signal rejection, and ease of use. The instrument is used to optically interrogate the flow in the Penn State University Supersonic Wind Tunnel and USAF AEDC Hypervelocity Tunnel 9 for measurement of the overall intensity and spectra of freestream disturbances. Precise characterization of the strength and spectral content of the disturbances provides insight into their nature and potential effect upon boundary layer transition. A special feature of the FLDI instrument used here is the replacement of traditional fixed Wollaston prisms with variable Sanderson prisms for laser-beam separation and recombination.
38 citations
Cites methods from "Laser schlieren crossed-beam measur..."
...Funk and Johnston[39] take the instrument used by Wilson for his UV absorption experiments and add knife-edges before the photodetectors, while replacing the UV sources with HeNe lasers, to perform crossed-beam schlieren measurements....
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...Funk and Johnston([39]) take the instrument used by Wilson for his UV absorption experiments and add knife-edges before the photodetectors, while replacing the UV sources with HeNe lasers, to perform crossed-beam schlieren measurements....
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TL;DR: In this article, the authors used a simple laser schlieren technique to obtain flow information in a two-dimensional separated compression ramp-induced shock-wave boundary-layer interaction, which was made at a freestream Mach number of 9 and freeestream Reynolds number per unit length of 2.078 × 105 m−1.
Abstract: This paper demonstrates the use of a simple laser schlieren technique to obtain flow information in a two-dimensional separated compression ramp-induced shock-wave boundary-layer interaction. Tests were made at a freestream Mach number of 9 and freestream Reynolds number per unit length of 2.078 × 105 m−1. The importance of this technique in studying hypersonic flows is unique since the run times of hypersonic wind tunnels are of very short duration. The method is based on the schlieren principle and uses a parallel sheet of a low-power (15 W) diode laser and an array of very fast response (4 ns) photodiodes. Although the arrangement detects an integral part of the signal from the fluctuating density gradients across the span of the flow, it yields significant insights into the details of the flow structure. The details of the flow field are discussed using time-dependent fluctuating density gradient profiles, the related power spectra and autocorrelation and cross-correlation functions in the interaction region.
24 citations
07 May 2004
TL;DR: In this article, the Lighthill tensor is revisited together with a brief evaluation of the state-of-the-art of the subject and an exploration of the possibility of further improvements in jet noise prediction from analytical methods, computational fluid dynamics (CFD) predictions, and measurement techniques.
Abstract: The acoustic analogy introduced by Lighthill to study jet noise is now over 50 years old. In the present paper, Lighthill s Acoustic Analogy is revisited together with a brief evaluation of the state-of-the-art of the subject and an exploration of the possibility of further improvements in jet noise prediction from analytical methods, computational fluid dynamics (CFD) predictions, and measurement techniques. Experimental Particle Image Velocimetry (PIV) data is used both to evaluate turbulent statistics from Reynolds-averaged Navier-Stokes (RANS) CFD and to propose correlation models for the Lighthill stress tensor. The NASA Langley Jet3D code is used to study the effect of these models on jet noise prediction. From the analytical investigation, a retarded time correction is shown that improves, by approximately 8 dB, the over-prediction of aft-arc jet noise by Jet3D. In experimental investigation, the PIV data agree well with the CFD mean flow predictions, with room for improvement in Reynolds stress predictions. Initial modifications, suggested by the PIV data, to the form of the Jet3D correlation model showed no noticeable improvements in jet noise prediction.
22 citations
TL;DR: In this article, the results of a series of measurements made using a single beam schlieren system to investigate the density fluctuations present in the initial region of a supersonic axisymmetric turbulent jet with a Mach number of 1-82 in the flow a t the nozzle exit were presented.
Abstract: This paper describes the results of a series of measurements made using a single beam schlieren system to investigate the density fluctuations present in the initial region of a supersonic axisymmetric turbulent jet with a Mach number of 1-82 in the flow a t the nozzle exit. A preheater was used to reduce the difference between the jet static temperature and that of the surrounding air to a relatively low level. The results show that significant density fluctuations are present in the potential core of the jet and that the distribution of fluctuating intensity across the shear layer differs from that obtained with a subsonic jet without preheating.
11 citations
9 citations
References
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TL;DR: In this article, the authors considered the case of laminar heat transfer over blunt-nosed bodies at hypersonic flight speeds, or high s tagnat ion temperatures, in which the chemical reaction rates are regarded as "very fas t" compared to the rates of diffusion across streamlines.
Abstract: This paper deals wi th two l imit ing cases of laminar heat transfer over blunt-nosed bodies at hypersonic flight speeds, or high s tagnat ion temperatures: (a) thermodynamic equil ibrium, in which the chemical reaction rates are regarded as "very fas t" compared to the rates of diffusion across streamlines; (b) diffusion as rate-governing, in which the volume recombination rates within the boundary layer are "very s low" compared to diffusion across streamlines. In either case the gas density near the surface of a blunt-nosed body is m u c h higher than the density jus t outside the boundary layer, and the velocity and stagnation enthalpy profiles are m u c h less sensitive to pressure gradient than in the more familiar case of moderate temperature differences. In fact, in case (a), the nondimensionalized enthalpy gradient at the surface is represented very accurately by the "classical" zero pressure gradient value, and the surface heat-transfer rate distribution is obtained directly in terms of the surface pressure distribution. In order to i l lustrate the method , this solution is applied to the special cases of an unyawed hemisphere and an unyawed, b lunt cone capped by a spherical segment . In the opposite l imit ing case where diffusion is ratecontrolling the diffusion equation for each species is reduced to the same form as the low-speed energy equation, except that the Prandtl number is replaced by the Schmidt number . The simplifications introduced in case (a) are also applicable here, and the expression for surface heat transfer rate is similar; the maximum value of the ratio between the rate of heat transfer by diffusion alone and by heat conduction alone in the case of thermodynamic equil ibrium is given by: (Prandtl n o . / S c h m i d t no.)'. When the diffusion coefficient is es t imated by taking a reasonable value of a tom-molecule collision cross section this ratio is 1.30. Additional theoretical and (especially) experimental studies are clearly required before these s imple results are accepted.
823 citations
TL;DR: Local turbulent properties of shear layer derived from covariance of two crossed perpendicular beams of radiation were derived from local turbulent properties as mentioned in this paper, where the covariance was derived from the local turbulent property of the shear layers.
Abstract: Local turbulent properties of shear layer derived from covariance of two crossed perpendicular beams of radiation
81 citations
TL;DR: In this article, Fox, R. L., and Schmit, L. A., presented a Structural Synthesis Capability for Integrally Stiffened Cylindrical Shells.
Abstract: References 1 Schmit, L. A., Morrow, W. M., and Richer, T. P., "A Structural Synthesis Capability for Integrally Stiffened Cylindrical Shells," AIAA Paper 68-327, Palm Springs, Calif., 1968. 2 Fox, R. L., and Schmit, L. A., "Advances in the Integrated Approach to Structural Synthesis," Journal of Spacecraft and Rockets, Vol. 3, No. 6, June 1966, pp. 858-866. 3 Fiacco, A. V. and McCormick, G. P., "The Sequential Unconstrained Minimization Technique for Nonlinear Programming, Primal-Dual Method," Management Science, Vol. 10, No 2 Jan. 1964, pp. 360-366. 4 Fiacco, A. V. and McCormick, G. P., "Computational Algorithm for the Sequential Unconstrained Minimization Technique for Nonlinear Programming," Management Science, Vol 10 No. 4, July 1964, pp. 601-617. 5 Ralston, A. and Wilf, H. S., Mathematical Methods for Digital Computers, Vol. I, Wiley, New York, 1960. 6 Faddeeva, V. N., Computational Methods in Linear Algebra, Dover, New York, 1959, pp. 79-84. 7 Fox, R. L. and Kapoor, M. P., "Rates of Change of Eigenvalues and Eigenvectors," AIAA Journal, Vol. 6, No. 12, 1968, pp. 2426-2429. 8 Kapoor, M. P., "Automated Optimum Design of Structures under Dynamic Response Restrictions," Rept. 28, 1969, Division of Solid Mechanics, Structures and Mechanical Design, Case Western Reserve University, Cleveland, Ohio. 9 Davidenko, D. F., "An Approximate Solution of System of Nonlinear Equations," Ukrain Journal of Mathematics, Vol. 5, No. 2, 1953, pp. 196-206. 10 Yakolev, M. N., "The Solutions of Systems of Nonlinear Equations by a Method of Differentiation with Respect to a Parameter," U.S.S.R. Comput. Math, and Mechanics, Pt. I, Vol 4, No. 1, 1964, pp. 198-203. 11 Kane, T. R., "Real Solutions of Sets of Nonlinear Equations," AIAA Journal, Vol. 4, No. 10, 1966, pp. 1880-1881. 12 Wilde, N. G., "A Note on a Differential Equation Approach to Nonlinear Programming," Management Science, Vol 15, No 11, 1969, p. 739.
9 citations