Unsteady separated flow in an axisymmetric configuration is investigated, with the objective of analyzing vortex-ring formation and break-up and the ensuing interactions believed to be leading to breakdown of laminar flow. The model problem considered is an idealized representation of a combustor with a centerbody. Direct solution of the time-dependent incompressible Navier-Stokes equations is employed, with central-differencing for all spatial derivatives, to determine the response of this flow for Re = 2000, 5000 and 10,000. The last case revealed a rather novel unsteady vortex-ring interaction phenomenon. This case has been further investigated using third-order accurate upwind differencing for the convective terms. The flow is interrogated carefully by examining the corresponding instantaneous vorticity, stream-function and velocity fields, as well as by tracking mass-less marker particles in some of the critical regions. Such detailed examination is deemed essential, prior to assigning fundamental physical relevance to the observed vortex-interaction phenomenon.

An analysis of the symmetric wake behind a circular cylinder is developed, using the two-dimensional form of the unsteady incompressible Navier-Stokes equations in terms of vorticity and stream function. The conservationlaw form of the equations is employed in generalized orthogonal curvilinear coordinates. A fully-implicit direct time-marching scheme consisting of the alternating direction implicitblockGaussian elimination (ADI-BGE) technique is employed. This method has overall secondorder spatial accuracy and, therefore, avoids the introduction of any artificial viscosity. After the major structure of the flow field has been established with the direct technique, an algorithm which corresponds to Newton b method is applied to increase the rate of convergence and the accuracy of the solution. The asymptotic flow structure which results from this analysis of the halfcylinder configuration compares favorably with existing numerical and analytical solutions.

A fast electronic field switch is described for field-dependent NMR experiments (relaxation dispersion, zero-field spectra, cross relaxation, etc.), which makes use of high-voltage thyristors and transistors (GTOs, MOSFETs) and thus allows production of cycles of the magnetic flux density B with much shorter transit intervals to the maximum field level than instruments previously reported in the literature. The switch controls a 3 kW power supply and gives dBdtmax = 6 × 102 T/s for Bmax = 0.21 T; a projected extension of the device to 50 kW driving power will increase either the maximum switching rate or the maximum field level by one order of magnitude. The performance of the switch is by measurements of the proton spin relaxation dispersion of samples with rather short relaxation times, namely in the millisecond range. Also shown are proton zero-field spectra of such systems, which cannot be obtained by means of the recently reported, inherently slow mechanical cycling devices because of the presence of fast longitudinal relaxation processes.

A fully implicit time-marching method is developed such that all spatial derivatives are approximated using central differences, but no use is made of any artificial dissipation. The numerical method solves the discretized equations using Alternating Direction Implicit-Block Gaussian Elimination technique. The method is implemented in the unsteady analysis, which solves the incompressible Navier-Stokes equations in terms of vorticity and stream function in generalized orthogonal coordinates. A clustered conformal C-grid is employed, and every effort is made to resolve the various length scales in the flow problem. The metric discontinuity at the branch-cut is treated appropriately using analytic continuation. Introduction of the BGE reordering permits implicit treatment of the branch cut in the numerical method. The vorticity singularity at the cusped trailing edge is also appropriately treated. This accurate and efficient implicit method is used to study flow at Re = 1000, past a 12-percent thick symmetric Joukowski airfoil at high angle of attack 30 and 53 deg.

Berichte der deutschen chemischen GesellschaftVolume 33, Issue 1 p. 278-317 Mittheilungen Ueber die Umwandlung von Farbbasen in Pseudoammonium-Hydrate, -Cyanide und -Sulfonsäuren A. Hantzsch, A. HantzschSearch for more papers by this authorG. Osswald, G. OsswaldSearch for more papers by this author A. Hantzsch, A. HantzschSearch for more papers by this authorG. Osswald, G. OsswaldSearch for more papers by this author First published: Januar–April 1900 https://doi.org/10.1002/cber.19000330142Citations: 62AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat References p278_1 Ber. dtsch. Chem. Ges. 32, 3109. p283_1 Ber. dtsch. Chem. Ges. 32, 1678. Journ. prakt. Chem. 47, 403. p283_2 Da das freie Auramin nicht ein Isomeres, sondern ein Anhydrid der echten Auraminammoniumbase ist, kann hier der Name Pseudoammoniumbase streng genommen nicht gebraucht werden. p283_3 Ber. dtsch. Chem. Ges. 22, 1879. p284_1 Ber. dtsch. Chem. Ges. 20, 2844. p285_1 Ber. dtsch. Chem. Ges. 23, 1788 und Ber. dtsch. Chem. Ges. 28, 1696. p287_2 Ber. dtsch. Chem. Ges. 26, 2211. p287_3 Zeitschrift f. Chemie 18, 6, 2. p287_4 Ber. dtsch. Chem. Ges. 28, 1703. p287_5 Ber. dtsch. Chem. Ges. 32, 3120. p290_1 Streng genommen, verdient sie wie das Auramin nicht den Namen Pseudoammoniumbase, da sie nicht ein Isomeres der echten Ammoniumbase ist, sondern aus Letzterer durch Anhydrisirung entsteht. p290_2 Die Formel vom Chinontypus ist nur wegen der Analogie mit den übrigen Farbstoffen gewählt, ohne sie damit der O. Fischer'schen Anhydrid-formel vorziehen zu wollen. p291_1 Ann. d. Chem. 292, 266. p292_1 Ber. dtsch. Chem. Ges. 31, 3073. p292_2 Ber. dtsch. Chem. Ges. 32, 597. p292_3 Ber. dtsch. Chem. Ges. 32, 1042. p292_4 Ann. d. Chem. 230, 144. p292_5 Ber. dtsch. Chem. Ges. 21, 1592. p292_6 Ber. dtsch. Chem. Ges. 28, 1578. p293_1 Ber. dtsch. Chem. Ges. 32, 597. p294_1 Ann. d. Chem. 230, 175. p29_91 Ber. dtsch. Chem. Ges. 28, 1696. p300_1 Ber. dtsch. Chem. Ges. 30, 555. p302_1 Ber. dtsch. Chem. Ges. 32, 3109. p311_1 Ber. dtsch. Chem. Ges. 21, 2621. p312_1 Ann. d. Chem. 256, 237. p314_1 Ann. d. Chem. 292, 266. p316_1 Ber. dtsch. Chem. Ges. 21, 1592. p316_2 Ann. d. Chem. 230, 139. Citing Literature Volume33, Issue1Januar–April 1900Pages 278-317 ReferencesRelatedInformation

Berichte der deutschen chemischen GesellschaftVolume 32, Issue 1 p. 641-650 Mittheilungen Ueber Cyanoform A. Hantzsch, A. HantzschSearch for more papers by this authorG. Osswald, G. OsswaldSearch for more papers by this author A. Hantzsch, A. HantzschSearch for more papers by this authorG. Osswald, G. OsswaldSearch for more papers by this author First published: Januar–April 1899 https://doi.org/10.1002/cber.18990320193Citations: 37AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume32, Issue1Januar–April 1899Pages 641-650 RelatedInformation