Shock Wave-boundary Layer Interaction in Supersonic Flow over Compression Ramp and Forward-Facing Step

Shock wave-boundary layer interactions (SWBLIs) have been studied ex-tensively due to their practical importance in the design of high speed ve-hicles. These interactions, especially the ones leading to shock induced separation are typically unsteady in nature and can lead to large fluctuating pressure and thermal loads on the structure. The resulting shock oscil-lations are generally composed of high-frequency small-scale oscillations and low-frequency large-scale oscillations, the source of the later being a subject of intense recent debate. Motivated by these debates, we study in the present work, the SWBLI at a compression ramp and on a forward-facing step (FFS) at a Mach number of 2.5. In the case of compression ramps, a few ramp angles are studied ranging from small (10 degree) ramp angle to relatively large values of up to 28 degrees. The FFS configuration, which consists of a 90 degree step of height h, may be thought of as an extreme case of the compression ramp geometry, with the main geometri-cal parameter here being (h/δ), where δis the thickness of the oncoming boundary layer. This configuration is less studied and has some inherent advantages for experimentally studying SWBLI as the size of the separa-tion bubble is large. In the present experimental study, we use high-speed schlieren, unsteady wall pressure measurements, surface oil flow visualiza-tion, and detailed particle image velocimetry (PIV) measurements in two orthogonal planes to help understand the features of SWBLI in the com-pression ramp geometry and the forward-facing step case. The SWBLI at a compression ramp has been more widely studied, and our measurements show the general features that have been seen in earlier studies. The upstream boundary layer is found to separate close to the ramp corner forming a separation bubble. The streamwise length of the separa-tion bubble is found to increase with the ramp angle, with a consequent shift of the shock foot further upstream. At very small ramp angles up to 10 degrees, there is no evidence of separation, while at large ramp angles of 28 degrees, the separation bubble extends upstream to about 3.5δ(δ=boundary layer thickness). In all cases, the separation bubble is however very small in the wall normal direction, typically known to be about 0.1δ, and hence is difficult to directly measure in experiments using PIV. Shock foot measurements using PIV show that the shock has a spanwise ripple, which seems directly related to the high-and low-speed streaks in the in-coming boundary layer as recently shown by Ganapathisubramani et al. (2007). The forward-facing step configuration may be thought of as an extreme case of the compression ramp geometry, with a ramp angle of 90 degrees. This configuration has not been extensively studied, and is experimentally convenient due to the large separation bubbles formed ahead of the step. In the present work, extensive measurements of the mean and unsteady flow around this configuration have been done, especially for the case of h/δ=2, where his the step height. Pressure measurements in this case, show clear low-frequency motions of the shock at non-dimensional frequencies of about fh/U∞≈ 0.02. In this case, PIV measurements show the pres-ence of a large mean separation bubble extending to about 4hupstream and about 1hvertically. Instantaneous PIV measurements have been done in both cross-stream (streamwise and wall-normal plane) and in the span-wise (streamwise-spanwise) plane. Instantaneous cross-stream PIV mea-surements show significant variations of the shock location and angle, be-sides large variations in the recirculation region (or separation bubble), this being determined as the area having streamwise velocities less than zero. From a large set of individual PIV instantaneous fields, we can estimate the correlation of the measured shock location to both downstream effects like the area of the recirculation region, and upstream effects like the presence of high-/low-speed streaks in the oncoming boundary layer. We find that the shock location measured from data outside the boundary layer is more highly correlated to downstream effects as measured through the recircu-lation area compared to upstream effects in the boundary layer. However, we find that the shock foot within the boundary layer has ripples in the spanwise direction which are well correlated to the presence of high-/low-speed streaks in the incoming boundary layer. These spanwise ripples are however found to be small (less than one h) compared to the highly three-dimensional shape of the recirculation region with spanwise variation of the order of 3 step heights. In summary, the study shows that the separated region ahead of the step is highly three-dimensional. The shock foot within the boundary layer is found to have ripples that are well correlated to fluctuations in the in-coming boundary layer. However, we find that the large-scale nearly two-dimensional shock motions outside the boundary layer are not well cor-related to the fluctuations in the boundary layer, but are instead well cor-related with the spanwise-averaged separation bubble extent. Hence, the present results suggest that for the forward-facing step configuration, it is the downstream effect caused by the separation bubble that leads to the observed low-frequency shock motions

Determination of the maturity stages of marine fishes

Determination of the maturity stages of marine fishe

Evaluation of the morphometric and meristic characters of fishes

To determine the body proportions, to prepare adult skeleton, to familiarise with staining technique for small specimens and to count vertebrae, spines and ray

Study of the ichthyofauna of the locality of work

To study the fish fauna at two centres, Mandapam and Pamban by making collections there; to study the characteristic features of various groups; and to identify the important species with the aid of literature (both in the field and in the laboratory

Seasonal landings of oil sardine, Sardinella longiceps at Rameswaram, Pamban and Mandapam areas

Unusual and unprecedented landings of oil sardine, Sardinella langiceps were noticed at Rameswaram and Pamban during January and February 1992. The estimated catch of oil sardine at Rameswaram for January- February 1992 was 4,561 t. The pair trawlers contributed 4,244 t and fish trawlers 317 t. The C/E varied from 1.5 to 8 t. At Pamban the pair trawling during the period realised 741 t

Some Notes On Queenfishes And Their Fishery Along The Indian Coasts

A large variety of fishes popularly called horse mackerels, shads, trevellies, queenfishes, pompanos, runners etc. comprise the family Carangidae. Among them, the subfamily Scomberoidae represented by the genus Scomberoides (- Chorinemus) is popularly knownas queenfishes.They form an important constituent in the marine fish landings of India. This article highlights some of the taxonomic characters for easy field identification and also to review in brief the status of fishery of this group of fishe

Nesting Pattern Preferences of Stingless Bee, Trigona Iridipennis Smith (Hymenoptera: Apidae) in Jnanabharathi Campus, Karnataka, India

The patterning aspects of nests are receiving increased attention in nature, so we have studied it in human-dwelling environments involving repeated spatio-temporal mold of pattern. Different criteria such as nesting sites, orientations, nest characters, longevity and elevation of nests have been selected to check the level of preferences exhibited by an indigenous resident species of stingless bee, Trigona iridipennis Smith at the Jnanabharathi campus in the southern part of Bangalore (Karnataka). Nesting patterns gave a precise measurement of preference level exhibited by testing different paradigms. The deciduous, shrub type of vegetation helped for successful dominance in higher number of nests to thrive well, which in turn helped to look at the varying patterns of nests. Observations on different nests revealed: i. preference for the habitats made of walls, ii. north facing direction for nest opening, iii. different type of nests with oval-shaped opening and medium-sized exposure outside, iv. nests with more accumulation of mud, resin and wax deposits and v. bees preferring middle elevation range of 11-15 feet for nest-building purely depending on the safer strategies such as availability of flora, protection from predators for better and safe survival at the nesting sites

Observation of Pure Spin Transport in a Diamond Spin Wire

Spin transport electronics - spintronics - focuses on utilizing electron spin as a state variable for quantum and classical information processing and storage. Some insulating materials, such as diamond, offer defect centers whose associated spins are well-isolated from their environment giving them long coherence times; however, spin interactions are important for transport, entanglement, and read-out. Here, we report direct measurement of pure spin transport - free of any charge motion - within a nanoscale quasi 1D 'spin wire', and find a spin diffusion length ~ 700 nm. We exploit the statistical fluctuations of a small number of spins ($\sqrt{N}$ < 100 net spins) which are in thermal equilibrium and have no imposed polarization gradient. The spin transport proceeds by means of magnetic dipole interactions that induce flip-flop transitions, a mechanism that can enable highly efficient, even reversible, pure spin currents. To further study the dynamics within the spin wire, we implement a magnetic resonance protocol that improves spatial resolution and provides nanoscale spectroscopic information which confirms the observed spin transport. This spectroscopic tool opens a potential route for spatially encoding spin information in long-lived nuclear spin states. Our measurements probe intrinsic spin dynamics at the nanometre scale, providing detailed insight needed for practical devices which seek to control spin.Comment: 7 pages, 2 figures, under consideration at Nature Nanotechnolog

Spiral Magnets as Gapless Mott Insulators

In the large $U$ limit, the ground state of the half-filled, nearest-neighbor Hubbard model on the triangular lattice is the three-sublattice antiferromagnet. In sharp contrast with the square-lattice case, where transverse spin-waves and charge excitations remain decoupled to all orders in $t/U$, it is shown that beyond leading order in $t/U$ the three Goldstone modes on the triangular lattice are a linear combination of spin and charge. This leads to non-vanishing conductivity at any finite frequency, even though the magnet remains insulating at zero frequency. More generally, non-collinear spin order should lead to such gapless insulating behavior.Comment: 10 pages, REVTEX 3.0, 3 uuencoded postscript figures, CRPS-94-0

Impact of heavy metals on water, fish (Cyprinus carpio) and sediments from a water tank at Tumkur, India

This study was carried out to assess the concentrations of various heavy metals and their distribution in a hyper-eutrophic urban Tumkur tank system, which is being polluted from industrial, domestic and sewage effluents. Samples of water, fish and soil sediment were analyzed for the concentration of seven heavy metals (iron, zinc, copper, nickel, chromium, lead and cadmium) using atomic absorption spectrophotometry. The water-soluble (bioavailable) fractions of heavy metals correlated positively with their total concentration, exhibiting the following sequence of bioavailability: Zn > Cd > Ni > Pb > Cu > Cr > Fe. Cyprinus carpio exhibited a maximum bioaccumulation factor for copper (5500). The mean values of all types of collected samples were correlated with the corresponding mean values in a control tank (Teetha tank). The sequence of the order of the concentration of the metals in water, fish and sediment samples exhibiting higher values than those observed in the control tank was as follows: Cr > Pb > Cu ≈ Ni > Fe > Cd > Zn, Cr > Cd > Cu ≈ Zn > Pb > Fe ≈ Ni and Fe > Pb > Cr > Cu > Ni > Zn > Cd, respectively. The geoaccumulation indices of the heavy metals revealed that the tank is moderately to strongly contaminated. As Cyprinus carpio is extensively used for human consumption, there is a growing health risk that these metals could find their way into the human food chain