Modern developments in shear flow control with swirl

Passive and active control of swirling turbulent jets is experimentally investigated. Initial swirl distribution is shown to dominate the free jet evolution in the passive mode. Vortex breakdown, a manifestation of high intensity swirl, was achieved at below critical swirl number (S = 0.48) by reducing the vortex core diameter. The response of a swirling turbulent jet to single frequency, plane wave acoustic excitation was shown to depend strongly on the swirl number, excitation Strouhal number, amplitude of the excitation wave, and core turbulence in a low speed cold jet. A 10 percent reduction of the mean centerline velocity at x/D = 9.0 (and a corresponding increase in the shear layer momentum thickness) was achieved by large amplitude internal plane wave acoustic excitation. Helical instability waves of negative azimuthal wave numbers exhibit larger amplification rates than the plane waves in swirling free jets, according to hydrodynamic stability theory. Consequently, an active swirling shear layer control is proposed to include the generation of helical instability waves of arbitrary helicity and the promotion of modal interaction, through multifrequency forcing

A study of three dimensional turbulent boundary layer separation and vortex flow control using the reduced Navier Stokes equations

A reduced Navier Stokes (RNS) initial value space marching solution technique was applied to vortex generator and separated flow problems and demonstrated good predictions of the engine face flow field. This RNS solution technique using FLARE approximations can adequately describe the topological and topographical structure flow separation associated with vortex liftoff, and this conclusion led to the concept of a subclass of separations which can be called vorticity separations: separations dominated by the transport of vorticity. Adequate near wall resolution of vorticity separations appears necessary for good predictions of these flows

The effects of streamline curvature and swirl on turbulent flows in curved ducts

A technique for improving the numerical predictions of turbulent flows with the effect of streamline curvature is developed. Separated flows, the flow in a curved duct, and swirling flows are examples of flow fields where streamline curvature plays a dominant role. A comprehensive literature review on the effect of streamline curvature was conducted. New algebraic formulations for the eddy viscosity incorporating the kappa-epsilon turbulence model are proposed to account for various effects of streamline curvature. The loci of flow reversal of the separated flows over various backward-facing steps are employed to test the capability of the proposed turbulence model in capturing the effect of local curvature. The inclusion of the effect of longitudinal curvature in the proposed turbulence model is validated by predicting the distributions of the static pressure coefficients in an S-bend duct and in 180 degree turn-around ducts. The proposed turbulence model embedded with transverse curvature modification is substantiated by predicting the decay of the axial velocities in the confined swirling flows. The numerical predictions of different curvature effects by the proposed turbulence models are also reported

Rectangular jet with shear layer swirl: Rotation & mixing enhancement

A rectangular jet emerging from a nozzle with embedded swirl vanes in its exit boundary layer is studied. The swirling shear layer imposes an external torque on the jet boundary where it causes jet rotation in the direction of axis switching, skew deformation as well as enhanced mixing. In moderate aspect ratio rectangular nozzles, e.g. AR = 5:1, a pair of co-rotating streamwise vortices is formed on the narrow boundary of the jet that dominates its dynamics in the near field. A vortex-induced model is developed that accounts for the rotation of the rectangular jet with embedded shear layer swirl. The model also shows that the jet rotation is diminished with increasing aspect ratio, as AR−2. The higher entrainment rate in the rotating jet with skew deformation causes the jet mass flow rate with shear layer swirl to be 20–25% higher than the corresponding plain rectangular nozzle of the same aspect ratio (x/De > 1). The proposed model is validated using computational simulation results of previous investigations that appeared in the literature

Asymmetrical Flow Simulation of Icing Effects in S-Duct Inlets at Angle of Attack

This is the published version

A Computational Investigation of Icing effects on an S-Duct Inlet

This is the published version. Copyright 2010 © Freund Publishing House Ltd.The effects of a typical glaze ice accretion shape on the performance of the M2129 S-duct inlet are computationally investigated for a range of flight Mach numbers. A Reynolds-Averaged Navier-Stokes (RANS) code with k-o> turbulence model is used to simulate the compressible viscous flow in the S-duct inlet. The glaze ice accretion on the cowl lip is modeled on a steady-state basis from NASA LEWICE3D code. The results show that the total pressure recovery is reduced and the compressor face distortion level is increased with flight Mach number. A reduction of 22.8% in total pressure recovery is calculated for a flight Mach number of 0.85 in fully-developed glazed ice condition. The massive flow separations in the inlet induced by the glaze ice horn shapes also create a mass flow reduction in the inlet between 27 and 33% as compared to clean inlet for flight Mach numbers of 0.13 and 0.475, respectively. The combined effects of reduced total pressure recovery and the reduced mass flow rate results in a reduction of engine thrust between ~30 and 60% from low speed flight to Mach 0.85

Passive Control of Supersonic Rectangular Jets through Boundary Layer Swirl

This is the published version.Mixing characteristics of under-expanded supersonic jets emerging from plane and notched rectangular nozzles are computationally studied using nozzle exit boundary layer swirl as a mean of passive flow control. The coupling of the rectangular jet instability modes, such as flapping, and the swirl is investigated. A three-dimensional unsteady Reynolds-Averaged Navier-Stokes (RANS) code with shock adaptive grids is utilized. For plane rectangular nozzle with boundary layer swirl, the flapping and spanwise oscillations are captured in the jet’s small and large dimensions at twice the frequencies of the nozzles without swirl. A symmetrical oscillatory mode is also observed in the jet with double the frequency of spanwise oscillation mode. For the notched rectangular nozzle with boundary layer swirl, the flapping oscillation in the small jet dimension and the spanwise oscillation in the large jet dimension are observed at the same frequency as those without boundary layer swirl. The mass flow rates in jets at 11 and 8 nozzle heights downstream of the nozzles increased by nearly 25% and 41% for the plane and notched rectangular nozzles respectively, due to swirl. The axial gross thrust penalty due to induced swirl was 5.1% for the plane and 4.9% for the notched rectangular nozzle

Robot path planning in a dynamic and unknown environment based on Colonial Competitive Algorithm (CCA) and fuzzy logic

Robot path planning has been one of the favorite areas for many Machine Learning researchers from the past up to date. The trajectory designed for a robot can be simple or complex. The robot must pass through obstacles which are either movable or fixed. One of the considerable ways for robot path planning in the dynamic and unknown environment is a combination of Evolutionary algorithm and Fuzzy logic. There are different kinds of evolutionary algorithms such as Genetic algorithm, Ant Colony algorithm, Colonial Competitive algorithm, etc. A new approach has been proposed in this paper for robot path planning in the dynamic and unknown environment based on both the Colonial Competitive algorithm and fuzzy rules. The implemented results of the proposed method present its superiority over previous methods which used only fuzzy logic method