Freestream

About: Freestream is a research topic. Over the lifetime, 3428 publications have been published within this topic receiving 56147 citations.

Temperature Measurements by Laser-Induced Fluorescence Spectroscopy in Nonequilibrium High-Enthalpy Flow

Abstract: The e owe eld generated by the high-enthalpy arcjet facility L2K, simulating the stagnation conditions during shuttlereentry and mainly used for testing thermal protection materials, is investigated by using the laser-induced e uorescence (LIF)diagnostictechnique.FortheoperationconditionsoftheL2KfacilityofDLR,thee owconditions are dominated by nonequilibrium effects. In particular, translational and rotational temperatures are assumed to beinequilibrium,butlargedifferencesbetweenrotational,vibrational,and electronictemperatureoccur.Spatially resolved LIF is used to determine rotational and translational temperature of NO molecules and O atoms in the freestream and behind a bow shock upstream of a blunt body. The e ow is modeled numerically using a quasione-dimensional code and a full Navier ‐Stokes two-dimensional axisymmetric code. Good agreement is achieved between the experimental and numerical data in the freestream. The data are also compared with the coherent Stokes anti-Raman scattering measurements performed previously at the same e ow conditions in the same facility on the N2 molecules. Differences caused by the nonequilibrium aspects, in the freestream and across the shock layer, of N2, NO, and O components are evident, and the physical interpretation is discussed.

Film Cooling from a Single Row of Compound Angle Holes at High Blowing Ratios

Abstract: Experimental results are presented which describe the development and structure of flow downstream of a single row of holes with compound angle orientations producing film cooling at high blowing ratios. This film cooling configuration is important because similar arrangements are frequently employed on the first stage of rotating blades of operating gas turbine engines. With this configuration, holes are spaced 6d apart in the spanwise direction, with inclination angles of 24 degrees, and angles of orientation of 50.5 degrees. Blowing ratios range from 1.5 to 4.0 and the ratio of injectant to freestream density is near 1.0. Results show that spanwise averaged adiabatic effectiveness, spanwise-averaged iso-energetic Stanton number ratios, surveys of streamwise mean velocity, and surveys of injectant distributions change by important amounts as the blowing ratio increases. This is due to injectant lift-off from the test surface just downstream of the holes.

Scalar Transport in a Swirling Transverse Jet

Abstract: The scalar transport in a swirling jet in a crossflow has been investigated in water tunnel experiments. The jet to freestream velocity ratio was varied from 4.9 to 11.1, and the jet swirl numbers ranged from 0 to 0.17. The jet exit Reynolds number was kept at 1.3 x 10 4 during the experiments. Planar laser-induced fluorescence was utilized to measure planar cross sections of the mean concentration field of the jet up to 68 jet diameters downstream of the exit. The jet penetration depth, half-value radius, and maximum concentration were determined from these concentration fields. For jets without swirl, measured cross-sectional mean concentration distributions have symmetric double-lobed kidney shapes that are consistent with the counter-rotating vortex pair that is known to exist in the far field of the jet. The addition of swirl causes the far-field distributions to become nonsymmetric, with one of the lobes increasing in size and the other decreasing, resulting in a comma shape. Swirl is also observed to decrease jet penetration but not to significantly affect the decay of maximum mean concentration for the range of swirl numbers investigated.

Internal cowl-separation at high incidence angles

Abstract: Internal flow separation at large incidence angles is studied on the basis of wind-tunnel pressure data for six axisymmetric inlet geometries. The inlet geometric variables investigated are the angle of incidence, the throat Mach number, the internal lip contraction ratio, 'sharpness' of the external shape, and freestream velocity. It is shown that an increase in lip contraction ratio delays internal flow separation, while an increase in the sharpness of the external profile tends to reduce the angle of incidence at which complete flow separation occurs. It is also shown that inlet flow separation is subject to scale effects associated with the boundary layer on the cowl surface. The scale effects are particularly pronounced at very high throat Mach numbers.