Topic

# Stagnation point

About: Stagnation point is a research topic. Over the lifetime, 5606 publications have been published within this topic receiving 106564 citations.

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1,422 citations

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TL;DR: In this article, a time-dependent three-space-dimensional laser beam propagation is described, where the authors use a discrete Fourier transform (DFT) method for diffraction problems.

Abstract: The computation of time-dependent three-space-dimensional laser beam propagation is described. The methods are applicable to the propagation of high energy laser beams through the atmosphere in the presence of a horizontal wind and turbulence for most situations of interest. Possible cases are propagation of cw beams through stagnation zones, multi-pulse propagation, including the self-consistent treatment of pulse self-blooming, and propagation involving transonic slewing. The solution of the Maxwell wave equation in Fresnel approximation is obtained by means of a discrete Fourier transform method, which, surprisingly, gives excellent results for diffraction problems. The latter provide a stringent test for the accuracy of any solution method. Considerable use is also made of discrete Fourier transform methods in solving the hydrodynamic equations. The treatment of turbulence is based on the generation of random phase screens at each calculation step along the propagation path. In a time-dependent calculation the random phase screens can be either made to move with the wind at a given propagation position or generated anew for each successive time.

1,105 citations

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TL;DR: In this article, the authors derived a correlation for the Nusselt number of the form suggested by this evidence using a selection of the data and showed that this exponent should be a function of nozzle-to-plate spacing and of the radial displacement from the stagnation point.

Abstract: Experimental data for the rate of heat transfer from impinging turbulent jets with nozzle exit Reynolds numbers in the range of 5,000–124,000 have been collated and critically reviewed from the considerable body of literature available on the subject. The geometry considered is that of a single circular jet impinging orthogonally onto a plane surface for nozzle-to-plate distances from 1.2–16 nozzle diameters and over a flow region up to six nozzle diameters from the stagnation point. Existing correlations for local heat transfer coefficient express Nusselt number as a function of nozzle exit Reynolds number raised to a constant exponent. However, the available empirical data suggest that this exponent should be a function of nozzle-to-plate spacing and of the radial displacement from the stagnation point. A correlation for Nusselt number of the form suggested by this evidence has been derived using a selection of the data. The review also suggests that the Nusselt number is independent of nozzle-to-plate spacing up to a value of 12 nozzle diameters at radii greater than six nozzle diameters from the stagnation point. The results from a simple extrapolation for obtaining heat transfer coefficients in the wall jet region compare favourably with published data.

1,030 citations

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TL;DR: In this paper, heat transfer characteristics of single and multiple isothermal turbulent air and flame jets impinging on surfaces are reviewed, and the effect of crossflow on impingement heat transfer is included.

Abstract: Heat transfer characteristics of single and multiple isothermal turbulent air and flame jets impinging on surfaces are reviewed. Both circular and slot two-dimensional jets are considered, and the effect of crossflow on impingement heat transfer is included. The emphasis is on physical phenomena and not on comparison of published empirical correlations or comparisons of theory and experiments. The review focuses on applications in the materials or comparisons of theory and experiments. The review focuses on applications in the materials processing field. In spite of the fact that there are many differences in the jet characteristics (ie, axial velocity and turbulence intensity) of isothermal and flame jets, the stagnation point heat transfer of these different jets can be described in a similar way. Areas needing research attention are also identified.

935 citations

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TL;DR: In this paper, a two-temperatur e chemical-kinet ic model for air is assessed by comparing theoretical results with existing experimental data obtained in shock tubes, ballistic ranges, and flight experiments.

Abstract: A two-temperatur e chemical-kinet ic model for air is assessed by comparing theoretical results with existing experimental data obtained in shock tubes, ballistic ranges, and flight experiments. In the model, one temperature (T) is assumed to characterize the heavy-particle translational and molecular rotational energies, and another temperature (Tv) the molecular vibrational, electron translational, and electronic excitation energies. The theoretical results for nonequilibrium flow in shock tubes are obtained using the computer code STRAP (shock-tube radiation program) and for flow along the stagnation streamline in the shock layer over spherical bodies using the newly developed code SPRAP (stagnation-point radiation program). Substantial agreement is shown between the theoretical and experimental results for relaxation times and radiative heat fluxes. At very high temperatures, the spectral calculations need further improvement. The present agreement provides strong evidence that the two-temperature model characterizes principal features of nonequilibriu m airflow. New theoretical results using the model are presented for the radiative heat fluxes at the stagnation point of 6 m radius sphere, representing an aeroassisted orbital transfer vehicle, over a range of freestream conditions. Assumptions, approximations, and limitations of the model are discussed. Nomenclature = average molecular speed ^/$kT/nm, cm s ~ ! = pre-exponential factor in reaction rate coefficient, cm3mole~ 1 s~ * - average vibrational energy per particle, erg = average vibrational energy per particle under equilibrium, erg = reaction energy, erg

690 citations