Downstream Ramp Research Articles

Discussion of “Discharge Characteristics of Weirs of Finite Crest Length with Upstream and Downstream Ramps” by Amir Hossein Azimi, Nallamuthu Rajaratnam, and David Z. Zhu

C. Di Stefano; V. Ferro; and M. Bijankhan, Aff.M.ASCE Researcher, Dipartimento di Scienze Agrarie e Forestali, Universita degli Studi di Palermo, Viale delle Scienze, Palermo 90128, Italy. E-mail: costanza.distefano@unipa.it Full Professor, Dipartimento di Scienze Agrarie e Forestali, Universita degli Studi di Palermo, Viale delle Scienze, Palermo 90128, Italy (corresponding author). E-mail: vito.ferro@unipa.it Ph.D. Candidate, Irrigation and Reclamation Engineering Dept., Univ. of Teheran Karaj, P.O. Box 31587-4111, Karaj 31587-77871, Iran. E-mail: bijankhan@ut.ac.ir

Discharge Characteristics of Weirs of Finite Crest Length with Upstream and Downstream Ramps

This paper considers flow measurement in open channels with transverse weirs of finite crest length with sloping crests and upstream or downstream ramps—or both—for free flows. Using the broad-crested weir equation with a discharge coefficient as the basis and following the earlier studies of broad-crested weirs, robust correlations have been developed for the discharge coefficient by using the experimental results available in the literature. Effects of upstream and downstream ramps were studied by introducing the upstream and the downstream length scales, respectively. The proposed correlations of embankment weirs were compared with the head-discharge formu- lations of embankment weirs in the literature. Triangular (hump) weirs with either upstream or downstream ramps (or both) have also been considered. It was found that in triangular (hump) weirs, the discharge coefficient increases when the downstream slope increases, but it decreases when the upstream slope increases. DOI: 10.1061/(ASCE)IR.1943-4774.0000519. © 2013 American Society of Civil Engineers. CE Database subject headings: Weirs; Embankments; Flow measurement; Open channel flow; Water flow; Slopes; Wave crest. Author keywords: Broad-crested weirs; Embankment weirs; Flow measurement; Hump; Open channel flow; Triangular weirs; Water flow.

Numerical Simulation of Injection Strategies in a Cavity-Based Supersonic Combustor

High-fidelity simulations with a validated methodology are employed to explore the physical processes associated with different injection strategies on supersonic combustion. The configurations consider a commonly employed open single-cavityflameholder. The effects of different injector locations and injection angles are examined under the constraint that the total fuel mass flow rate is the same. The numerical approach solves the full three-dimensional Navier–Stokes equations, supplemented with a two-equation k-! turbulence closure. The specific injection locations include 10 different arrangements that examine fuel injection upstream of the cavity, on the backward step, on the cavity bottom wall, and on the downstream ramp. The angles of the fuel port injection slots include combinations of parallel and 27 and 90 deg to the airflow inside the cavity. One case with a closed cavity is also examined for comparison. The simulations are employed to characterize the performancewith qualitative andquantitativemixing metrics. Detailed analysis of the results reveals both expected and unexpected findings. As anticipated, the closed cavity performs poorly relative to its open counterpart. However, an injection strategy that enhances the natural circulation pattern of the cavity is found to be superior to one that opposes it. Another counterintuitive finding is that although direct injection of the fuel upstream of the cavity into themain stream results in deeper penetration, the fuel from different injectors remains distinct, with relatively small spanwise mixing. On the other hand, injection on the floor of the cavity results in more diffused fuel distribution.

Large-Eddy Simulation of Plasma-Based Turbulent Boundary-Layer Separation Control

A large-eddy simulation (LES) was carried out in order to numerically describe the use of plasma-based actuation for the control of turbulent boundary-layer separation. The configuration consisted of a flat plate section over which the boundary layer developed, followed by a curved convex rearward-facing ramp, corresponding to an experimental arrangement. A single dielectric-barrier-discharge (DBD) plasma actuator was then employed to reduce the extent of the separated flow region. Solutions were obtained to the Navier-Stokes equations, that were augmented by source terms used to represent plasma-induced body forces imparted by the actuator on the fluid. A simple phenomenological model provided the electric field generated by the plasma, resulting in the body forces. The numerical method utilized a high-fidelity time-implicit scheme, employing domain decomposition in order to perform calculations on a parallel computing platform. Simulations were first conducted for an isolated actuator in the absence of external flow, which were used to optimize the choice of parameters inherent in the plasma model. Subsequently, actuation was applied to the plate development section without the downstream ramp section. Following these computations, the complete plate/ramp configuration was simulated. In all cases, both continuous and pulsed operation of the actuator was considered. Comparisons are made with available experimental data, and with baseline flows where no control was enforced. The large separated flow region characterizing the baseline flow for the plate/ramp configuration was well captured by the simulation. When continuous control was applied, separation was almost entirely eliminated. Pulsing operation of the actuator using a 40% duty cycle was not as eective, but did result in a considerable reduction of the recirculating zone. The control cases compared reasonably well with experimental measurements. Although deficiencies in the plasma model were apparent in the near-wall region, it appeared to be adequate for use with LES in the exploration of plasma-based control for turbulent wall-bounded flows.

Driver choice compared to controlled diversion for a freeway double on-ramp in the framework of three-phase traffic theory

Two diversion schemes that apportion demand between two on-ramps to reduce congestion and improve throughput on a freeway are analyzed. In the first scheme, drivers choose to merge or to divert to a downstream on-ramp based on information about average travel times for the two routes: (1) merge and travel on the freeway or (2) divert and travel on a surface street with merging downstream. The flow, rate of merging at the ramps, and the travel times oscillate strongly, but irregularly, due to delayed feedback. In the second scheme, diversion is controlled by the average mainline velocities just upstream of the on-ramps. Driver choice is not involved. If the average upstream velocity on the mainline drops below a predetermined value (20 m/s) vehicles are diverted to the downstream ramp. When the average mainline velocity downstream becomes too low, diversion is no longer permitted. The resultant oscillations in this scheme are nearly periodic. The period is dominated by the response time of the mainline to interruption of merging rather than delayed feedback, which contributes only a minor component linear in the distance separating the on-ramps. In general the second scheme produces more effective congestion reduction and greater throughput. Also the travel times for on-ramp drivers are less than that obtained by drivers who attempt to minimize their own travel times (first scheme). The simulations are done using the Kerner–Klenov stochastic three-phase theory of traffic [B.S. Kerner, S.L. Klenov, Phys. Rev. E 68 (2003) 036130].

A simulation approach for examining capacity and operational performance at freeway diverge areas

Freeway diverge areas, and particularly those in the proximity of exit ramps, are often viewed as potential bottlenecks in freeway operations. The existing diverge procedures within the 1994 and 1997 Highway Capacity Manual updates are limited in that they do not provide a direct estimate of freeway capacity nor do they model performance at oversaturated traffic conditions. Moreover, a parallel investigation on these procedures revealed some inconsistencies in predicting measures of performance at those critical areas. This paper describes the use of computer traffic simulation to explore the patterns of capacity and operational performance behaviour at these areas under the impact of some key geometric and traffic variables. For this purpose, the microscopic traffic simulation model INTEGRATION was selected to conduct an extensive experimental work on a typical ramp-freeway diverge section. Five control variables were investigated, namely, total upstream demand, off-ramp demand, length of deceleration lane, off-ramp free-flow speed, and number of lanes at mainline. The impact of upstream or downstream ramps is considered beyond the scope of this research. Except for off-ramp free-flow speed, the impact of other control variables on capacity and operational performance was shown to be significant. Also, the simulated trends of traffic behaviour showed considerable agreement with logic and expectations in light of the current state of knowledge on freeway operations.Key words: freeways, diverge, capacity, operations, traffic simulation.

Experimental Investigation of the Role of Downstream Ramps on a Supersonic Injection Plume

An experimental study was conducted to investigate penetration and plume expansion enhancement of a discrete low-angled (25 deg) supersonic (M =1.9) injection into a supersonic (M =2.9) crosse ow. The enhancement was achieved by injecting the low-angled jet parallel to a compression ramp. Seven compression ramp cone gurations were studied. The jet-ramp interaction enhancement mechanisms included baroclinic torque vorticity, ramp spillage vorticity, bulk compression, and the Magnus force. Shadowgraph photography was used to identify shock structures. Measurements of mean e ow properties quantie ed the e owe eld total pressure losses. Mie scattering images were used to qualitatively assess the e owe eld and to quantify the plume size, trajectory, and concentration decay rate. The results indicated that up to a 22% increase in penetration, a 39% plume expansion (» mixing), and a 27% increase in the concentration decay rate, with a corresponding 17% increase in total pressure loss, can be achieved by injection over a compression ramp as compared with low-angled injection alone.

Hydraulic filling of dams constructed of silty soils, using a flattened profile

1. Construction experience and experimental investigations established that it is advantageous to use silty soils for the construction of dams with a flattened profile, consisting of a downstream impervious shoulder (hydraulic fill) and upstream wave-resistant ramp (dumped material). This design eliminates the construction of massive shoulders of gravel-pebble material which are needed in hydraulic filling of compressed dams of disperse soils. 2. Flattened dams, depending on the content of sand particles in the disperse soils, are constructed by unilateral hydraulic filling with limitation of the upstream slope or by unilateral hydraulic filling with bypass of the soil-water mixture into settling pools arranged on the section of the upstream ramp. With both methods the stability of the dam is provided during construction by layerwise consolidation of the soil. The wave-resistant ramp, constructed beforehand by dumping soil, eliminates the need of an upstream slope revetment and provides stepwise filling of the reservoir. 3. In the case of unilateral hydraulic filling with bypass of the soil-water mixture into settling pools the quality of the soil placed in the impervious shoulder improves. In this case the carry-off of soil with the drain water does not exceed 5%, whereas with hydraulic filling by the old technology carry-off averaged 25% 4. The cost of constructing a flattened dam for a height up to 15 m is about 3% less than the cost of a compressed dam with gravel shoulders, and with consideration of the reduction of soil carry-off the construction cost is reduced additionally by 10–15% in the case of hydraulic filling by the recommended technology with placement of settling pools on the section of the upstream ramp. 5. In hydraulic filling of dams by the recommended technology labor productivity increases 19% owing to the reduction of soil losses and decrease of manpower. 6. When planning construction operations, it is necessary to take into account the basic parameters characterizing the technological process: rate of hydraulic filling designated so as to provide layerwise consolidation of the soil and calculated by Eq. (1) and the optimal layers of hydraulic fill and dumped soil in the settling pools, determined by Eqs. (5) and (6).