The Bursting of Leading-Edge Vortices - Some Observations and Discussion of the Phenomenon

The term bursting refers to the structural change from a strong regular spiral motion to a weaker turbulent motion which can occur at some position along a vortex. Various observations of this phenomenon have been recorded during low-speed tunnel investigations of vortex flows generated from sharp, swept back leading edges. These reveal a sudden deceleration of fluid along the vortex axis and expansion of the vortex around a stagnant core downstream of which the flow is turbulent; it is possible at very low stream velocity to see the axial flow, after deceleration, deflect and perform a regular whirling motion before turbulent breakdown. These features together with the effects of bursting on oil-flow patterns and pressures at the wing surface are illustrated and described. Brief reference is made to observations at transonic speeds. The burst is found to be sensitive to several factors, in particular, an increase of pressure gradient along the vortex seems conducive to the occurrence of a burst. It is suggested that a condition essential for the burst to occur is a low total pressure within the vortex core coupled with an adverse pressure gradient along the axis. When bursting occurs in the flow above a plain wing it is likely that the occurrence is related to the adverse pressure gradient associated with the existence of a trailing edge. The experiments described in Appendix I show that a similar type of phenomenon can occur in the flow in a vortex tube

Pressure probes selected for three-dimensional flow measurement

Seven pressure probes have been tested in a uniform stream in order to ascertain the best types for measuring velocity and flow direction. Methods of calibration are discussed in section 8 together with the effects of wind speed, flow direction and turbulence on the calibration factors (section 4). The performance of three of the probes in the turbulent boundary layer of a flat plate is analysed and their accuracies compared when they are used to estimate displacement and momentum thicknesses (section 6). The Conrad probe is proved superior to other types for boundary-layer measurements. Further research on the lines indicated in section 7 is necessary before the best type of probe for use in regions of separated flow can be ascertained. The main features of the velocity-measuring probes are listed in Table 4. For measuring static pressure in three-dimensional flow, a disc type of probe is described and shown to be insensitive to flow direction and scale effect (section 5)

Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV

A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7 TeV is presented. The data were collected at the LHC, with the CMS detector, and correspond to an integrated luminosity of 4.6 inverse femtobarns. No significant excess is observed above the background expectation, and upper limits are set on the Higgs boson production cross section. The presence of the standard model Higgs boson with a mass in the 270-440 GeV range is excluded at 95% confidence level.Comment: Submitted to JHE

Combined search for the quarks of a sequential fourth generation

Results are presented from a search for a fourth generation of quarks produced singly or in pairs in a data set corresponding to an integrated luminosity of 5 inverse femtobarns recorded by the CMS experiment at the LHC in 2011. A novel strategy has been developed for a combined search for quarks of the up and down type in decay channels with at least one isolated muon or electron. Limits on the mass of the fourth-generation quarks and the relevant Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a simple extension of the standard model with a sequential fourth generation of fermions. The existence of mass-degenerate fourth-generation quarks with masses below 685 GeV is excluded at 95% confidence level for minimal off-diagonal mixing between the third- and the fourth-generation quarks. With a mass difference of 25 GeV between the quark masses, the obtained limit on the masses of the fourth-generation quarks shifts by about +/- 20 GeV. These results significantly reduce the allowed parameter space for a fourth generation of fermions.Comment: Replaced with published version. Added journal reference and DO

Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV

The performance of muon reconstruction, identification, and triggering in CMS has been studied using 40 inverse picobarns of data collected in pp collisions at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection criteria covering a wide range of physics analysis needs have been examined. For all considered selections, the efficiency to reconstruct and identify a muon with a transverse momentum pT larger than a few GeV is above 95% over the whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4, while the probability to misidentify a hadron as a muon is well below 1%. The efficiency to trigger on single muons with pT above a few GeV is higher than 90% over the full eta range, and typically substantially better. The overall momentum scale is measured to a precision of 0.2% with muons from Z decays. The transverse momentum resolution varies from 1% to 6% depending on pseudorapidity for muons with pT below 100 GeV and, using cosmic rays, it is shown to be better than 10% in the central region up to pT = 1 TeV. Observed distributions of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO

The behaviour of the leading-edge vortices over a delta wing following a sudden change of incidence

Summary. The trafisient behaviour of leading-edge vortices over a delta wing subject to a sudden change of incidence is of importance in understanding the wing loadings that can occur in unsteady conditions of flight. In the experiments reported here, changes of incidence have been imposed on delta-shaped plates by application of a constant-velocity plunging motion for a limited time; other related unsteady motions are discussed in the Appendix. Ciné records of particle tracks and of dye filaments in a water tunnel have been analysed to trace the time history of vortex centres in cross-flow planes following the application of step-changes of incidence. The flows for various combinations of initial incidence, planform, plunging velocity and chordwise position have been examined. Results indicate that after the start of the plunge an effectively steady vortex system is established over the plate in a time approximately equal to that required for one chord length of relative forward travel. Where comparisons can be made, Dore's theoretical calculations of the manner in which the vortices move show fair agreement with the experiment. Effects of the transient movements of the vortices on lift distribution are discussed and the inference is drawn that the changes in the distribution of wing loading occurring for an increase of incidence are not simply reversed when the incidence is decreased

Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV

The performance of muon reconstruction, identification, and triggering in CMS has been studied using 40 inverse picobarns of data collected in pp collisions at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection criteria covering a wide range of physics analysis needs have been examined. For all considered selections, the efficiency to reconstruct and identify a muon with a transverse momentum pT larger than a few GeV is above 95% over the whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4, while the probability to misidentify a hadron as a muon is well below 1%. The efficiency to trigger on single muons with pT above a few GeV is higher than 90% over the full eta range, and typically substantially better. The overall momentum scale is measured to a precision of 0.2% with muons from Z decays. The transverse momentum resolution varies from 1% to 6% depending on pseudorapidity for muons with pT below 100 GeV and, using cosmic rays, it is shown to be better than 10% in the central region up to pT = 1 TeV. Observed distributions of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO