Flow Development through a Duct and a Diffuser Using CFD

This paper presents the observations of an experimental work dealing with the measurement of normalized mean velocity and wall static pressure of a 90° C-shaped curved duct. The test duct is made up of transparent perspexsheet to facilitate the flow visualization study. The duct has a centerline distance of 750mm. The Inlet and Outlet aspect ratio of the test duct used is 1.0. Wall pressures are measured with the help of an inclined manometer withthe inclination of 35°. The manometer had two tubes emanating from it: one left open to the atmosphere and the other connected to the steel pipes attached to the four walls of the curved duct. The difference in the readings helped calculate the static pressure and thereby the normalized pressure. Wall pressure distribution along the curved and parallel walls of the duct at 0°, 22.5°, 45°, 67.5° and 90° measuring sections was measured. The investigation for wall static pressure distribution is carried out at the velocity of 40m/s. This paper also presents an experimental work carried out with measurement of normalized mean velocity of the mentioned curved square C shaped duct, taken at the same velocity. The trend of the normalized mean velocity contour development inside the C duct shows continuous decrease of the normalized velocity as we move from the Inlet Section towards the Outlet Section. The distribution of wall static pressure and normalized mean velocity contours are mapped by using SURFER software package. The trend of wall static pressure development on the walls of C shaped duct shows that as the flow proceeds towards the curvature, there exists a high pressure gradient between the Outside Face and Inside Face due the centrifugal force acting along the curvature. This shows the bulk shifting of flow towards the Inside Face. This is due to the generation of secondary motion in a plane perpendicular to the primary flow. The main purpose of this investigation is to show the development of secondary flow which happens when the flow takes place through the bend in the curvature. This secondary flow arises as a result of a centrifugal force acting when the flow moves through the bend.

2007

Curved channels are very often present in real hydraulic systems, e.g. curved diffusers of hydraulic turbines, Sshaped bulb turbines, fittings, etc. Curvature brings change of velocity profile, generation of vortices and production of hydraulic losses. Flow simulation using CFD techniques were performed to understand these phenomena. Cases ranging from single elbow to coupled elbows in shapes of U, S and spatial right angle position with circular cross-section were modeled for Re = 60000. Spatial development of the flow was studied and consequently it was deduced that minor losses are connected with the transformation of pressure energy into kinetic energy and vice versa. This transformation is a dissipative process and is reflected in the amount of the energy irreversibly lost. Least loss coefficient is connected with flow in U-shape elbows, biggest one with flow in S-shape elbows. Finally, the extent of the flow domain influenced by presence of curvature was examined. This is impo...

International Journal of Aerodynamics, 2010

A computational investigation is carried out to study the flow and performance characteristics of a Y-shaped diffusing duct having two inlets and one outlet with an overall area ratio of 2 using a commercial CFD code, FLUENT. The CFD code is validated with the experimental results and it was found that the code applying the RNG k-e turbulence model has the capability of predicting the flow and performance characteristics for the similar geometry. The Y-shaped diffusing duct is formed by merging two symmetrical S-shaped diffusing ducts (area ratio = 4, curvilinear length = 600 mm, angle of turn = 22.5°/22.5°) at the centreline of outlet. The flow and performance characteristics of the duct are analysed for a uniform flow profile at the inlet that is observed in the experiments. The results are presented in the form of contour plots for the axial velocity distribution and the cross-flow velocity distribution in terms of vector plots. The analysis reveals the fact that however the flow at the diffuser inlet is uniform, secondary flows are induced as an effect of curvature and change in the cross-sectional area.

Mechanika, 2011

International Journal of Turbo & Jet-Engines, 2019

The effect of aspect ratio (AS = 0.5, 1.0, 2.0) and Reynolds number (Re = 1, 2, 4, 8 × 105) on the flow and performance characteristics of a 90° curved rectangular diffuser was examined with the aid of the commercial CFD code ANSYS FLUENT. The results from computational analysis revealed the presence of stream vorticity indicative of secondary flow brought about by the curvature of the diffusing duct. As the fluid flow developed, the inertial core flow was pushed to the outer concave wall by overbearing centrifugal forces. The fluid flow sustained marginal changes with increasing aspect ratio and Reynolds number. However, the flow uniformity at the exit was enhanced. The rise in coefficient of static pressure (Cp) recovery and the drop in coefficient of total pressure loss (Closs) with increasing Reynolds number suggested improved diffuser performance. The flow uniformity index was found to be the highest for the diffuser of aspect ratio 1.

Transstellar Journals, 2019

This paper discusses about the Flow analysis of Aerospace ducts of Equipment cooling system of an aircraft. Equipment Cooling is provided to maintain assigned temperature conditions in equipment compartment for satisfactory working of Line Replaceable units (LRUs), which are installed inside equipment compartment. Forced air cooling is provided to these LRUs using Air Conditioning system (ACS) air. The life span of aircraft is approximately 30-40 years, and various up-gradations are required to be carried out to meet the operational &mission requirements. Up-gradation programmes of aircraft required installation of new LRUs, thus a requirement of redistribution of flow through complex duct geometries to meet their additional cooling requirements is mandatory. In the present practice, designers carryout the redistribution of flow of air through these complex ducts using Continuity & Bernoulli's equation. It was experienced that new LRUs at so many times not function properly due to inadequate cooling condition resulting malfunctioning of LRUs. This Paper aims to identify the reason for not achieving the designed cooling condition at designated LRUS. To analyse the flow through Aerospace ducts in transient condition, an experimental Environmental Control System (ECS) test rig has been newly designed to simulate the actual layout of installation of Aerospace ducts into aircraft. Theoretical analysis correlated by experimental trials analysis was carried out on Environmental Control System Test Rig. The results analysed and concluded the reason for not achieving the required cooling to LRUs. Notations ρ = Density of air µ = Dynamic Viscosity ν = Kinematic Viscosity m* =Mass flow rate m 13 = air mass flow rate in branch 13 V= Initial Velocity of the air f = Darcy friction factor Re = Reynolds no of flow (h f) 01 = Head loss due To Friction in section 0 to1 h f) 13 = Head loss due To Friction in section 1 to3 V 01 = Mean velocity between section 0 & 1 V 13 = Mean velocity between section 1 & 3. E 0 = Energy at the section 0 E 1 = Energy at the section 1 E 3 = Energy at the section 3 P 0 = Pressure drop at section 0 P 1 = Pressure drop at section 1 P 3 = Pressure drop at section 3 D 01 = Diameter of sections 0 to 1 D 13 = Diameter of sections 1 to 3 A 01 = Area of sections 0 to 1 A 13 = Area of sections 1 to 3 L 01 = Length of sections 0 to 1 L 13 = Length of sections 1 to 3 ε = Surface roughness

Journal of Fluids Engineering, 1990

The pressure driven, fully developed turbulent flow of an incompressible viscous fluid in curved ducts of square cross-section is studied numerically by making use of a finite volume method. A nonlinear K -1 model is used to represent the turbulence. The results for both straight and curved ducts are presented. For the case of fully developed turbulent flow in straight ducts, the secondary flow is characterized by an eight-vortex structure for which the computed flowfield is shown to be in good agreement with available experimental data. The introduction of moderate curvature is shown to cause a substantial increase in the strength of the secondary flow and to change the secondary flow pattern to either a double-vortex or a four-vortex configuration.

2021

In this paper, the velocity and pressure drop distribution in flowing water through circular, square, rectangular with aspect ratio of 2:1 and 4:1 as well as an equilateral triangle cross-sectional ducts with the same duct length and hydraulic diameter have been numerically studied using ANSYS FLUENT tools. The boundary conditions used for the simulation are: at the entrance a velocity inlet of 0.2 m/s at 25 C constant temperature, at exit a pressure outlet with zero gage pressure and a non-slip is used for the duct walls condition. A steady state and kepsilon turbulence flow model is used. The results have shown that velocity in the ducts gradually increases from zero at the walls to the maximum at the center. In the circular duct 20.327%, 15.273%, 13.5% and 6.834% more pressure is lost than in triangular, square, rectangular aspect ratio of 2:1 and rectangular aspect ratio of 4:1 ducts respectively. In turn, circular duct requires the highest pumping power while triangular one nee...

Transstellar Journals, 2019

After burners are employed in an aero engine of a fighter aircrafts, to achieve maximum thrust during takeoff , climb and during some special combat maneuvers. Since the fuel consumption is high during the afterburning operation it is employed only when necessary. The diffuser duct is the first component of the afterburner system, situated immediately next to the exit of the low-pressure turbine. The struts are the supporting structures, which connect the parts of diffuser duct. These struts will guide the flow in the diffuser duct. The presence of the struts will cause some pressure losses. The flow is decelerated in the diffuser duct. The Mach number also reduces along the length of the diffuser. The design of the diffuser duct should be made so that the recirculation should be minimum at the exit of the diffuser and the thermodynamics properties at the exit should meet the requirement for the proper mixing of the fuel and air with the hot gases passing through the diffuser & hence ensures complete combustion in the upstream zones of the diffuser. The flow inside an afterburner is highly complex due to the presence of the diffuser, flame stabilizer, variable area nozzle and the interaction between core and bypass flow through anti-screech holes. Therefore the performance of afterburner depends to a great extent on the internal aerodynamics. Experimental analysis of such flow is a difficult task. Cost and time involved for optimization design are very high. Computational fluid dynamics (CFD) provides a cost effective solution in analyzing. Its suitability to support the combustion process for the design of short efficient reheats system. Hence in this study, the flow in the diffuser duct in details by carrying out the analysis of subsonic flows in a three-dimensional model of an afterburner duct using CFD. The flow in the bypass region of the duct is considered, as it does not have any impact on diffuser performance. In the current study two stages viz. diffuser duct with struts and without struts were carried out and for both cases the pressure recovery, total pressure loss, essential flow properties like Mach number, velocity, statics pressure, swirl are compared for both the cases. Considering the periodicity of geometry, analysis has been carried out using 45-degree sector model of the diffuser duct with and without struts. Using ICEM-CFD pre-processor an unstructured grid has been generated and Navier-stroke equation is applied to carry out using ANSYS CFX CFD software, flow simulated by solving governing equation of mass, momentum, energy. Turbulence closure is achieved with k-epsilon turbulence model with standard wall functions.

Powder Technology, 2009

Gas-solid two-phase flow in 180°curved duct is simulated using a two-way coupling Eulerian-Lagrangian approach. Reynolds averaged Navier-Stokes equations (RANS) and four turbulence models namely; standard k-ε model, RNG (Renormalization Group) based k-ε model, Low-Re k-ε model and an extended version of the standard k-ε model are adopted. The effects of particle rotation and lift forces are included in the particle tracking model. The present predictions are compared with published experimental data for single-phase and two-phase flows. The comparisons show that the RNG based k-ε model predicts the flow behaviour better than other models. Furthermore, the particles concentration and velocity are compared very well with published data. The effects of inlet gas velocity, bend geometry, loading ratio and particle size on the flow behaviour and bend pressure drop are also discussed. The results show that the flow behaviour is greatly affected by these parameters.