scholarly journals Inline-Slot Ejector Diffuser for a Warship to Suppress IR Signatures

2019 ◽  
Author(s):  
L Singh ◽  
S. N. Singh ◽  
S. S. Sinha
Keyword(s):  
Temperature Distribution ◽  
Turbulence Intensity ◽  
Power Plants ◽  
Static Pressure ◽  
Pressure Recovery ◽  
Swirl Number ◽  
Potential Core ◽  
Mass Entrainment ◽  
Inlet Swirl ◽  
Cumulative Mass

The infrared (IR) signatures emitted by warships can substantially reduce the survivability chances while operating in the enemy area, as these signatures can be tracked and locked-on by the heat seeking missiles. The primary source for the IR signatures in a warship is the gases emanating from the exhaust of the gas turbine engine. These signatures can be suppressed by installing the passive infrared suppressors such as ejector diffusers, downstream of the turbine exhaust. The prime objective of an ejector diffuser is to reduce the exhaust gases temperature with minimal back pressure. In the present investigation, inline-slot conical ejector diffuser is numerically studied. From the open literature it is found that only step-slot ejector diffuser has been explored and no work on the inline-slot ejector diffuser is reported. Preliminary investigations on the inline-slot ejector diffuser show the performance to be better in terms of mass entrainment and static pressure recovery than the step-slot ejector diffuser, which is commonly used with warship power plants. The focus of the present study is to establish the effect of nozzle exit conditions (i) inlet swirl (S), and (ii) inlet turbulence intensity (TI) on the performance of inline-slot ejector diffuser. In the first part, inlet swirl is varied in the range 0≤S≤0.3 in step of 0.05, and in the second part TI is varied in the range of 1%≤TI≤15% in step of 3%. The performance is evaluated in terms of local and cumulative mass entrainment ratios, non-dimensional temperature distribution, and static pressure recovery. For the first part, it is seen that there is 3% drop in cumulative mass entrainment with the increase in swirl number from 0 to 0.3 and this can be attributed to the drop in potential core region. Higher wall temperatures in the mixing tube are observed for all the configurations with swirl cases. Static pressure recovery increases with the increase in the swirl number. For the second part, the effect of turbulence intensity on the performance of inline slot ejector diffuser is carried out. It is seen that the mass entrainment decreases by ~5% when turbulence intensity is increased from 1% to 15%. No significant effect of turbulence intensity is seen on the temperature distribution and pressure recovery.

Effect of Prediffuser Angle on the Static Pressure Recovery in Flow Through Casing-Liner Annulus of a Gas Turbine Combustor at Various Swirl Levels

2015 ◽  
Vol 8 (1) ◽  
Author(s):  
Prakash Ghose ◽  
Amitava Datta ◽  
Achintya Mukhopadhyay
Keyword(s):  
Gas Turbine ◽  
Static Pressure ◽  
Numerical Study ◽  
Pressure Recovery ◽  
Gas Turbine Combustor ◽  
Pressure Losses ◽  
Pressure Distributions ◽  
Inlet Swirl ◽  
Flow Through ◽  
The Ideal

A numerical study has been performed in an axisymmetric diffuser followed by a casing-liner annulus of a typical gas turbine combustor to analyze the flow structure and pressure recovery in the geometry. Static pressure recovery in a gas turbine combustor is important to ensure high pressure of air around the liner. However, the irreversible pressure losses reduce the static pressure recovery from the ideal value. The presence of swirl in the flow from compressor and prediffuser geometry before the dump diffuser influences the flow pattern significantly. In this study, flow structures are numerically predicted with different prediffuser angles and inlet swirl levels for different dump gaps. Streamline distributions and pressure plots on the casing and liner walls are analyzed. Static pressure recovery coefficients are obtained from the pressure distributions across the combustor. The effect of dump gap on the static pressure recovery has also been evaluated. It is observed that the best static pressure recovery can be obtained at optimum values of inlet swirl level and prediffuser angle. Dump gap is found to have significant influence on the static pressure recovery only at small prediffuser angle.

Effect of Swirl on Pressure Recovery in Annular Diffusers

1980 ◽  
Vol 22 (6) ◽  
pp. 305-313 ◽  
Author(s):  
D. S. Kumar ◽  
K. L. Kumar
Keyword(s):  
Cross Sections ◽  
Static Pressure ◽  
Tangential Velocity ◽  
Pressure Recovery ◽  
Test Facility ◽  
Pressure Loss Coefficient ◽  
Pressure Distributions ◽  
Inlet Swirl ◽  
Total Pressure Loss Coefficient ◽  
Different Levels

Annular diffusers are likely to operate with varying amounts of swirl at the inlet. The work described in this paper is concerned mainly with an experimental investigation of subsonic turbulent swirling flows through annular diffusers having diverging hub and casing boundaries. The test facility was designed SO as to peImit different levels of inlet swirl. The static pressure distributions and the axial and tangential velocity profiles were measured with the help of a three-hole cobra probe suitably mounted at different cross sections along the diffuser length. The diffuser performance parameters such as static-pressure recovery, effectiveness, and the total pressure loss coefficient were then computed from the experimental observations. The behaviour of these parameters has been discussed to establish the effect of swirl. The presence of inlet swirl was found to increase the overall static-pressure recovery. A substantial increase in the pressure recovery occurred over the initial stages of diffusion and the gain was maintained thereafter. Improvement in effectiveness was more significant for otherwise stalled diffusers. Introduction of swirl was found to substantially reduce the chances of separation at the casing and to shift the stall from the casing to the hub for the stalled diffusers.

Effects of casing angle on the performance of parallel hub axial annular diffuser

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Hardial Singh ◽  
B.B. Arora
Keyword(s):  
Static Pressure ◽  
Swirling Flow ◽  
Pressure Recovery ◽  
Recovery Coefficient ◽  
Pressure Loss Coefficient ◽  
Swirl Angle ◽  
Annular Diffuser ◽  
Inlet Swirl ◽  
Total Pressure Loss Coefficient ◽  
Pressure Recovery Coefficient

Abstract In this paper, the effects of non-swirling and swirling flow on the performance of parallel hub axial annular diffuser has been investigated. The study was conducted on a fully developed swirling flow and non-swirling flow to predict the separation of the flow from the wall. Three different annular diffusers were used with casing wall angles of 3°, 6°, and 9°. Furthermore, various swirl angles (0–25°) at the inlet of diffusers have been investigated to analyze the performance across the length. It was found that parallel hub axial annular diffuser performance increases up to a certain length as the inlet swirl angle increases. However, the performance also improves as the diffuser area ratio (AR) increases. The performance is evaluated based on the static pressure recovery coefficient (Cp) and the total pressure loss coefficient (CTL). The highest possible pressure recovery is achieved by the 12° swirl angle with a casing angle of 6°.

Strut Losses in a Diverging Annular Diffuser With Swirling Flow

2006 ◽  
Author(s):  
G. K. Feldcamp ◽  
A. M. Birk
Keyword(s):  
Total Pressure ◽  
Swirling Flow ◽  
Pressure Recovery ◽  
Swirl Number ◽  
Pressure Losses ◽  
Swirl Angle ◽  
Wide Range ◽  
Annular Diffuser ◽  
Inlet Swirl ◽  
The Ideal

An experimental investigation into the overall influence of struts spanning a double divergent annular diffuser followed by a straight cored annular diffuser has been undertaken in order to determine the performance of various strut configurations over a wide range of inlet swirl conditions. Two strut profiles have been investigated in four and eight strut configurations. Results have shown that the presence of struts under no swirl conditions have a relatively small effect on the overall total pressure loss. Increasing the inlet swirl angle to 20° has shown that the struts are able to assist in recovery of the swirling flow such that the pressure recovery nearly approaches that without struts, despite increased total pressure losses. Performance at 40° swirl is highly dependent on strut profile; the higher thickness-to-chord ratio strut configurations show minimal decrease in pressure recovery compared to 20° swirl, while the lower thickness-to-chord ratio configurations experiences a significant decrease as the result of significant flow separation from the struts. The exit swirl number has been shown to correlate strongly with the strut profile shape, while the number of struts had only a secondary influence. The exit velocity profiles show significant distortions at 40° swirl, and as a result the ideal pressure recovery calculated from the inlet and exit profiles change with strut configuration at 40° swirl.

Effect of Swirl on the Performance of an Annular Diffuser

2015 ◽  
Vol 787 ◽  
pp. 318-321
Author(s):  
R. Prakash ◽  
V. Karthik Srinivas ◽  
H. Anand ◽  
G. Adithya ◽  
N. Lakshmi Narayanan
Keyword(s):  
General Pattern ◽  
Pressure Recovery ◽  
Maximum Pressure ◽  
Swirl Number ◽  
Number Range ◽  
Flow Parameters ◽  
Efficient Performance ◽  
Annular Diffuser ◽  
Inlet Swirl ◽  
Numerical Variation

Annular diffusers are primarily used to convert the kinetic energy of the exhaust flow into pressure energy. The performance of the diffusers are often measured using pressure recovery maps, that generally do not consider the distortion of flow at the inlet due to other upstream machine components. A high swirl velocity at the inlet could often account for large energy losses and hence it is necessary to curb the swirl component by appropriate design considerations. In this present work,it is desired to establish the swirl number range at the inlet of an annular diffuser for its effective and efficient performance and increased pressure recovery of the diffuser. “Swirl effect” on the fluid flow parameters with and without struts is compared, to give the idea of the numerical variation in the parameters.Computational fluid dynamics (CFD) analysis was performed to determine the maximum pressure recovery based on variations in the inlet swirl number. Thus, the flow was studied under varied conditions and a relation between the input parameters and the general pattern of flow for the specified input conditions was critically examined.

scholarly journals Effects of casing angle on the performance of parallel hub axial annular diffuser

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Hardial Singh ◽  
B.B. Arora
Keyword(s):  
Static Pressure ◽  
Swirling Flow ◽  
Pressure Recovery ◽  
Recovery Coefficient ◽  
Pressure Loss Coefficient ◽  
Swirl Angle ◽  
Annular Diffuser ◽  
Inlet Swirl ◽  
Total Pressure Loss Coefficient ◽  
Pressure Recovery Coefficient

AbstractIn this paper, the effects of non-swirling and swirling flow on the performance of parallel hub axial annular diffuser has been investigated. The study was conducted on a fully developed swirling flow and non-swirling flow to predict the separation of the flow from the wall. Three different annular diffusers were used with casing wall angles of 3°, 6°, and 9°. Furthermore, various swirl angles (0–25°) at the inlet of diffusers have been investigated to analyze the performance across the length. It was found that parallel hub axial annular diffuser performance increases up to a certain length as the inlet swirl angle increases. However, the performance also improves as the diffuser area ratio (AR) increases. The performance is evaluated based on the static pressure recovery coefficient (Cp) and the total pressure loss coefficient (CTL). The highest possible pressure recovery is achieved by the 12° swirl angle with a casing angle of 6°.

scholarly journals Inlet Swirl and Dump Gap Effect on Static Pressure Recovery in Dump Diffuser-Combustor using Two Equation Turbulence Model

2020 ◽  
Vol 9 (5) ◽  
pp. 1214-1223
Keyword(s):  
Bluff Body ◽  
Static Pressure ◽  
Weighted Average ◽  
Pressure Recovery ◽  
Gap Effect ◽  
Cold Flow ◽  
Inlet Swirl ◽  
Flow Through ◽  
Turbulent Models ◽  
Flow Variables

Cold flow through an axi-symmetric dump diffuser, provided with a swirl effect at inlet is studied by using various two equation k-ε turbulent models such as; standard k-ε, RNG k- ε and Realizable k-ε model. There is a liner with a liner dome head of hemispherical in shape is used as a bluff body. From the comparison in between the three k-e turbulent models, it has been observed that the overall prediction of flow variables with Realizable k-e model are much better than others. The effects of dump gap and inlet swirl on velocity distribution and pressure variation on liner and casing walls have been investigated. The static pressure recovery within the diffuser is evaluated from area weighted average pressure at inlet and exit plane. It is noticed that an optimum inlet swirl results in the most effective pressure recovery due to the minimum irrecoverable energy dissipation in the vortices formed in the domain. The optimum swirl number is found to be 0.38 and it occurs when DG (non-dimensional dump gap) is kept as 1.0. The variation in dump gap changes the flow pattern and the possible pressure recovery. As the dump gap is increased, the static pressure is recovered more effectively with moderate swirl level in the inlet flow.

Performance characteristics of flow in annular diffuser using CFD

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Hardial Singh ◽  
Bharat Bhushan Arora
Keyword(s):  
Swirling Flow ◽  
Flow Behavior ◽  
Pressure Recovery ◽  
Ansys Fluent ◽  
Pressure Loss Coefficient ◽  
Swirl Angle ◽  
Swirl Intensity ◽  
Annular Diffuser ◽  
Inlet Swirl ◽  
Total Pressure Loss Coefficient

Abstract An annular diffuser is a critical component of the turbomachinery, and its prime function is to reduce the flow velocity. The current work is carried to study the effect of four different geometrical designs of an annular diffuser using the ANSYS Fluent. The numerical simulations were carried out to examine the effect of fully developed turbulent swirling and non-swirling flow. The flow behavior of the annular diffuser is analyzed at Reynolds number 2.5 × 105. The simulated results reveal pressure recovery improvement at the casing wall with adequate swirl intensity at the diffuser inlet. Swirl intensity suppresses the flow separation on the casing and moves the flow from the hub wall to the casing wall of the annulus region. The results also show that the Equal Hub and Diverging Casing (EHDC) annular diffuser in comparison to other diffusers has a higher static pressure recovery (C p  = 0.76) and a lower total pressure loss coefficient of (C L  = 0.12) at a 17° swirl angle.

Effect of the turning angle on the flow and performance characteristics of long S-shaped circular diffusers

2003 ◽  
Vol 217 (1) ◽  
pp. 29-41 ◽  
Author(s):  
R B Anand ◽  
L Rai ◽  
S N Singh
Keyword(s):  
Total Pressure ◽  
Static Pressure ◽  
Area Ratio ◽  
Secondary Flows ◽  
Performance Characteristics ◽  
Pressure Recovery ◽  
Recovery Coefficient ◽  
Turning Angle ◽  
And Performance ◽  
Pressure Recovery Coefficient

The effect of the turning angle on the flow and performance characteristics of long S-shaped circular diffusers (length-inlet diameter ratio, L/Di = 11:4) having an area ratio of 1.9 and centre-line length of 600 mm has been established. The experiments are carried out for three S-shaped circular diffusers having angles of turn of 15°/15°, 22.5°/22.5° and 30°/30°. Velocity, static pressure and total pressure distributions at different planes along the length of the diffusers are measured using a five-hole impact probe. The turbulence intensity distribution at the same planes is also measured using a normal hot-wire probe. The static pressure recovery coefficients for 15°/15°, 22.5°/22.5° and 30°/30° diffusers are evaluated as 0.45, 0.40 and 0.35 respectively, whereas the ideal static pressure recovery coefficient is 0.72. The low performance is attributed to the generation of secondary flows due to geometrical curvature and additional losses as a result of the high surface roughness (~0.5 mm) of the diffusers. The pressure recovery coefficient of these circular test diffusers is comparatively lower than that of an S-shaped rectangular diffuser of nearly the same area ratio, even with a larger turning angle (90°/90°), i.e. 0.53. The total pressure loss coefficient for all the diffusers is nearly the same and seems to be independent of the angle of turn. The flow distribution is more uniform at the exit for the higher angle of turn diffusers.

Influence of Turbulent Flow Characteristics and Coherent Vortices on the Pressure Recovery of Annular Diffusers: Part A — Experimental Results

2015 ◽  
Author(s):  
Marcus Kuschel ◽  
Bastian Drechsel ◽  
David Kluß ◽  
Joerg R. Seume
Keyword(s):  
Boundary Layer ◽  
High Pressure ◽  
Static Pressure ◽  
Turbulent Transport ◽  
Axial Flow ◽  
Pressure Recovery ◽  
Turbulence Structure ◽  
Reynolds Stresses ◽  
Wide Range ◽  
Operating Points

Exhaust diffusers downstream of turbines are used to transform the kinetic energy of the flow into static pressure. The static pressure at the turbine outlet is thus decreased by the diffuser, which in turn increases the technical work as well as the efficiency of the turbine significantly. Consequently, diffuser designs aim to achieve high pressure recovery at a wide range of operating points. Current diffuser design is based on conservative design charts, developed for laminar, uniform, axial flow. However, several previous investigations have shown that the aerodynamic loading and the pressure recovery of diffusers can be increased significantly if the turbine outflow is taken into consideration. Although it is known that the turbine outflow can reduce boundary layer separations in the diffuser, less information is available regarding the physical mechanisms that are responsible for the stabilization of the diffuser flow. An analysis using the Lumley invariance charts shows that high pressure recovery is only achieved for those operating points in which the near-shroud turbulence structure is axi-symmetric with a major radial turbulent transport component. This turbulent transport originates mainly from the wake and the tip vortices of the upstream rotor. These structures energize the boundary layer and thus suppress separation. A logarithmic function is shown that correlates empirically the pressure recovery vs. the relevant Reynolds stresses. The present results suggest that an improved prediction of diffuser performance requires modeling approaches that account for the anisotropy of turbulence.

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