Characteristics of Multi-Cavity Trapped Vortex Combustors

2010 ◽  
Author(s):  
Alejandro M. Briones ◽  
Balu Sekar
Keyword(s):  
Heat Release ◽  
Temperature Profile ◽  
Viscous Drag ◽  
Reacting Flow ◽  
Total Drag ◽  
Pressure Drag ◽  
Air Jets ◽  
Exit Temperature ◽  
Trapped Vortex ◽  
Single Cavity

This research is motivated towards improving and optimizing the performance of AFRL’s Inter-Turbine Burner (ITB) in terms of greater combustion efficiency, reduced losses and exit temperature profile requirements. The ITB is a minicombustor concept, situated in between the high and low pressure turbine stages and typically contains multiple fueled and non-fueled Trapped Vortex Combustor (TVC) cavities. The size, placement, and arrangement of these cavities have tremendous effect on the combustor exit temperature profile. The detailed understanding of the effect of these cavities in a three-dimensional ITB configuration would be very difficult and computationally prohibited. Therefore, a simple but somewhat similar conceptual axi-symmetric burner is used here the design variations of Trapped Vortex Combustor (TVC) through modeling and simulation. The TVC can be one single cavity or can be represented by multi-cavity combustor. In this paper, both single cavity TVC and multi-cavity TVCs are studied. The single cavity TVC is divided into multiple cavities while the total volume of the combustor remains constant. Four combustors are studied: Baseline, Staged, Three-Staged, and Interdigitated TVC. An extensive computational investigation on the characteristics of these multi-cavity TVCs is presented. FLUENT is used for modeling the axisymmetric reacting flow past cavities using a global eddy dissipation mechanism for C3H8-air combustion with detailed thermodynamic and transport properties. Calculations are performed using Standard, RNG, and Realizable k-ε RANS turbulence models. The numerical results are validated against experimental temperature measurements on the Base TVC. Results indicate that the pressure drag is the major contributor to total drag in the Base TVC. However, viscous drag is still significant. By adding a concentric cavity in sequential manner (i.e. Staged TVC), the pressure drag decreases, whereas the viscous drag remains nearly constant. Further addition of a secondary concentric cavity (i.e. Three-Staged TVC), the total drag does not further decrease and both pressure and viscous drag contributions do not change. If instead a non-concentric cavity is added to the Base TVC (i.e. Interdigitated TVC), the pressure drag increases while the viscous drag decreases slightly. The effect of adding swirl flow is to increase the fuel-air mixing and as a result, it increases the maximum exit temperature for all the combustors modeled. The jets and heat release contribute to increase pressure drag with the former being greater. The fuel and air jets and heat release also modify the cavity flow structure. By turning off the fuel and air jets in the Staged TVC, lower drag (or pressure loss) and exit temperature are achieved. It is more effective to turn off the fuel and air jets in the upstream (front) cavity in order to reduce pressure losses. Based on these results, recommendations are provided to the engineer/designer/modeler to improve the performance of the ITB.

scholarly journals Temperature Profile Development in Turbulent Mixing of Coolant Jets With a Confined Hot Cross Flow

1983 ◽  
Author(s):  
S. L. K. Wittig ◽  
O. M. F. Elbahar ◽  
B. E. Noll
Keyword(s):  
Temperature Profile ◽  
Momentum Flux ◽  
Cross Flow ◽  
Field Methods ◽  
Opposite Wall ◽  
Hot Gas ◽  
Air Jets ◽  
Primary Zone ◽  
Exit Temperature ◽  
Wall Injection

The mixing of coolant air jets with the hot gas exiting the primary zone is of major importance to the combustor exit temperature profile. Geometry and momentum flux ratios are the dominant parameters. A theoretical and experimental study of single as well as opposite wall jet injection into a hot cross flow reveals the applicability and limitations of existing correlations. Modified correlations are presented for opposite wall injection with jets of different momentum flux ratios. The advantages in applying field methods for describing the flow are discussed.

Effect of the Compressor Discharge Casing Geometry on Combustor Exit Temperature Profiles in a Multi-Can Gas-Turbine Combustor

2014 ◽  
Author(s):  
Krishna Kant Agarwal ◽  
Stefano Gori
Keyword(s):  
Temperature Profile ◽  
Gas Turbine ◽  
Thermal Stresses ◽  
Flow Behavior ◽  
Thermal Design ◽  
Reacting Flow ◽  
Asymmetric Distribution ◽  
Gas Temperature ◽  
Flow Features ◽  
Exit Temperature

Temperature profile variations in gas turbine combustors are important from the considerations of thermal stresses and material fatigue. The specific profile being addressed in this study is the combustor exit gas temperature profile in radial direction at first stage nozzle entry (also called the combustor transition-piece (TP) exit profile). Normally, in multi-can combustor configurations, this profile is assumed to be constant along the circumferential direction or from one can to another. However, field test on one of the GE-MS5002D class machine revealed that the shape of the combustor TP exit temperature profile is varying across the different cans. It is important to assess the reason of this behavior in order to define thermal input for stage 1 nozzle thermal design and define an average temperature profile for turbine bucket verification. For investigating the reasons of varying TP exit profiles across different cans, a reacting flow CFD study is performed for a combined multiple combustor-cans geometry. This is a challenging attempt considering that mesh for a single can liner is itself typically quite large (∼30 million) for capturing all flow features. The present multi-can study was made feasible with judicious simplification of combustor geometry, retaining only important flow features and using adequate mesh to capture system physics. Results indicate that the varying flame shape across different cans is indeed captured in the CFD. Hence, this effect could be something associated with the combustor design. Subsequent detailed post-processing of CFD results revealed the root cause to be associated with the presence of unsymmetrical arrangement of struts in the compressor discharge casing region. This effect is a slight flow-recirculation created much upstream due to the struts, which eventually results in asymmetric distribution of the flow across the combustor dilution holes. This leads to the flame shifting in different orientation for different cans with a systematic reference to the struts position. In conclusion, this paper describes the approach used for multi-can CFD analysis of the combustor, flow behavior in presence of unsymmetrical strut and its impact on the combustor exit temperature profile much downstream.

scholarly journals Effect of Speed and Boot Opening on Aerodynamics, Fuel Consumption, and CO2 Emission of Minibus

2021 ◽  
Vol 6 (4) ◽  
Author(s):  
Olusola A. Oloruntoba ◽  
Adebunmi P. Okediji
Keyword(s):  
Fuel Consumption ◽  
Co2 Emission ◽  
Regression Models ◽  
Viscous Drag ◽  
Vehicle Speed ◽  
Road Accidents ◽  
Total Drag ◽  
Pressure Drag ◽  
Regulatory Bodies ◽  
Excess Load

Overspeeding   and overloading contribute to road accidents. In developing countries, overloading is often indicated by open boot due to commercial transporters’ motivation to carry an excess load to boost revenue. Therefore, there is a need to provide measures to control or eliminate the practice of overspeeding and overloading. This study aims to conduct a parametric study to determine the effect of vehicle speed and boot opening on the aerodynamics of airflow around a typical minibus, fuel consumption, and CO2 emission, and recommend optimum boot opening. Computational Fluid Dynamics is employed using the FLUENT™ program. Results show the existence of a wavy pattern for drag coefficient, fuel consumption, and CO2 emission concerning boot opening. Furthermore, two boot opening regions exist:  and . The first region exhibits low prediction error (maximum of 7.25%) and better fit of regression model to FLUENT™ data. The first region also has lower susceptibility to exhibit handling instability. Therefore, boot opening around  is recommended as the optimum boot opening, to ensure minimum fuel consumption and CO2 emissions, improve handling and safety. The developed regression models could inform regulatory bodies’ formulation and implementation of policies to mitigate road accidents. Keywords—Boot Opening, CO2 emission, Fuel Consumption, Pressure drag, Total Drag, Minibus, Viscous Drag

Numerical Analysis of Drag Reduction Characteristics of Biomimetic Puffer Skin: Effect of Spinal Height and Tilt Angle

2021 ◽  
Vol 21 (9) ◽  
pp. 4615-4624
Author(s):  
Hong-Gen Zhou ◽  
Chang-Feng Jia ◽  
Gui-Zhong Tian ◽  
Xiao-Ming Feng ◽  
Dong-Liang Fan
Keyword(s):  
Drag Reduction ◽  
Tilt Angle ◽  
Fluid Velocity ◽  
Viscous Drag ◽  
Total Drag ◽  
Pressure Drag ◽  
Reduction Efficiency ◽  
Distribution Parameters ◽  
Reduction Effect ◽  
Reduction Characteristics

Based on the migratory phenomenon of the puffer and the cone-shaped structures on its skin, the effects of spinal height and tilt angle on the drag reduction characteristics is presented by numerical simulation in this paper. The results show that the trend of total drag reduction efficiency changes from slow growth to a remarkable decline, while the viscous drag reduction efficiency changes from an obvious increase to steady growth. The total and viscous drag reduction efficiencies are 19.5% and 31.8%, respectively. In addition, with the increase in tilt angle, the total drag reduction efficiency decreases gradually; the viscous drag reduction efficiency first increases and then decreases, finally tending to be stable; and the total and viscous drag reduction efficiency reaches 20.7% and 26.7%, respectively. The flow field results indicate that the pressure drag mainly originates at the front row of the spines and that the total pressure drag can be effectively controlled by reducing the former pressure drag. With the increase in low-speed fluid and the reduction in the near-wall fluid velocity gradient, the viscous drag can be weakened. Nevertheless, the drag reduction effect is achieved only when the decrement of viscous drag is greater than the increment of pressure drag. This work can serve as a theoretical basis for optimizing the structure and distribution parameters of spines on bionic non-smooth surfaces.

Temperature Profile Development in Turbulent Mixing of Coolant Jets With a Confined Hot Crossflow

1984 ◽  
Vol 106 (1) ◽  
pp. 193-197 ◽  
Author(s):  
S. L. K. Wittig ◽  
O. M. F. Elbahar ◽  
B. E. Noll
Keyword(s):  
Temperature Profile ◽  
Momentum Flux ◽  
Jet Injection ◽  
Field Methods ◽  
Opposite Wall ◽  
Hot Gas ◽  
Air Jets ◽  
Primary Zone ◽  
Exit Temperature ◽  
Wall Injection

The mixing of coolant air jets with the hot gas exiting the primary zone is of major importance to the combustor exit temperature profile. Geometry and momentum flux ratios are the dominant parameters. A theoretical and experimental study of single as well as opposite-wall jet injection into a hot crossflow reveals the applicability and limitations of existing correlations. Modified correlations are presented for opposite-wall injection with jets of different momentum flux ratios. The advantages in applying field methods for describing the flow are discussed.

Combustion Characteristics of a Two-Dimensional Twin Cavity Trapped Vortex Combustor

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
P. K. Ezhil Kumar ◽  
D. P. Mishra
Keyword(s):  
Reynolds Number ◽  
Temperature Profile ◽  
Equivalence Ratio ◽  
Flame Length ◽  
Pollutant Emission ◽  
Air Velocity ◽  
Emission Level ◽  
Unburned Hydrocarbon ◽  
Exit Temperature ◽  
Trapped Vortex

Trapped vortex combustor (TVC) is a relatively new concept, having potential application in gas turbine engines. In this work, an attempt has been made to characterize the 2D twin cavity TVC experimentally in terms of its visible flame length, pollutant emission level, and exit temperature profile. Besides this, numerical results are also discussed to explain certain intricacies in flow and flame characteristics. Experimental results reveal that visible flame length value is sensitive to mainstream Reynolds number (Rems), primary (cavity) air velocity (Vp), and cavity equivalence ratio (Φc). For a particular Rems and Φc, an increase in Vp results in longer flame length; whereas, flame length gets shortened at higher mainstream Reynolds number cases. Numerical studies indicate that shortening of flame length at higher Rems cases is caused due to quenching of flame at the shear layer by the incoming flow. An attempt has been made to correlate flame length data with the operating parameters and Damkohler number (Da); Da takes care of flame quenching effects. Moreover, it is also brought out that the emission profile at the combustor exit is dependent on primary air velocity, mainstream Reynolds number, and cavity equivalence ratio. Emission studies indicate that higher primary air velocity cases make the carbon monoxide (CO) and unburned hydrocarbon (UHC) emission levels to lower values. Reduction in emission level is caused mainly due to the flame merging effects. Besides this, the influence of cavity flame merging on the exit temperature profile uniformity is also brought out. This study reveals that merging of cavity flames is essential for the optimized operation of a 2D trapped vortex combustor.

Numerical Studies on Trapped-Vortex Concepts for Stable Combustion

1998 ◽  
Vol 120 (1) ◽  
pp. 60-68 ◽  
Author(s):  
V. R. Katta ◽  
W. M. Roquemore
Keyword(s):  
Drag Coefficient ◽  
Reacting Flow ◽  
Flow Conditions ◽  
Third Order ◽  
Cold Flow ◽  
Flow Simulations ◽  
Numerical Studies ◽  
Dynamic Flows ◽  
Experimental Findings ◽  
Trapped Vortex

Spatially locked vortices in the cavities of a combustor aid in stabilizing the flames. On the other hand, these stationary vortices also restrict the entrainment of the main air into the cavity. For obtaining good performance characteristics in a trapped-vortex combustor, a sufficient amount of fuel and air must be injected directly into the cavity. This paper describes a numerical investigation performed to understand better the entrainment and residence-time characteristics of cavity flows for different cavity and spindle sizes. A third-order-accurate time-dependent Computational Fluid Dynamics with Chemistry (CFDC) code was used for simulating the dynamic flows associated with forebody-spindle-disk geometry. It was found from the nonreacting flow simulations that the drag coefficient decreases with cavity length and that an optimum size exists for achieving a minimum value. These observations support the earlier experimental findings of Little and Whipkey (1979). At the optimum disk location, the vortices inside the cavity and behind the disk are spatially locked. It was also found that for cavity sizes slightly larger than the optimum, even though the vortices are spatially locked, the drag coefficient increases significantly. Entrainment of the main flow was observed to be greater into the smaller-than-optimum cavities. The reacting-flow calculations indicate that the dynamic vortices developed inside the cavity with the injection of fuel and air do not shed, even though the cavity size was determined based on cold-flow conditions.

Enhanced vortex stability in trapped vortex combustor

2010 ◽  
Vol 114 (1155) ◽  
pp. 333-337 ◽  
Author(s):  
S. Vengadesan ◽  
C. Sony
Keyword(s):  
Numerical Simulation ◽  
Vortex Flow ◽  
Cavity Size ◽  
Vortex Stability ◽  
Cold Flow ◽  
Air Jets ◽  
Passive Flow ◽  
Flow Through ◽  
Trapped Vortex ◽  
Driver Air

Abstract The Trapped Vortex Combustor (TVC) is a new design concept in which cavities are designed to trap a vortex flow structure established through the use of driver air jets located along the cavity walls. TVC offers many advantages when compared to conventional swirl-stabilised combustors. In the present work, numerical investigation of cold flow (non-reacting) through the two-cavity trapped vortex combustor is performed. The numerical simulation involves passive flow through the two-cavity TVC to obtain an optimum cavity size to trap stable vortices inside the second cavity and to observe the characteristics of the two cavity TVC. From the flow attributes, it is inferred that vortex stability is achieved by circulation and the vortex is trapped inside when a second afterbody is added.

CFD Analysis of the Combustion Chamber of a Commercial Aircraft Engine of Medium Thrust Class From a Maintenance Perspective

2017 ◽  
Author(s):  
Stefan Kuntzagk ◽  
Jörn Kraft ◽  
Ina Esemann
Keyword(s):  
Combustion Chamber ◽  
Temperature Profile ◽  
Measurement Errors ◽  
Burning Velocity ◽  
Combustion Model ◽  
Cfd Analysis ◽  
Hexahedral Mesh ◽  
Flow Topology ◽  
Geometrical Features ◽  
Exit Temperature

The combustion chamber of aircraft engines plays an important role in achieving the optimum performance during an engine overhaul. For long decades, it has been common understanding in the MRO business that a well overhauled compressor and turbine are required to get an engine with low SFC and high EGT margin. In recent work at Lufthansa Technik AG, a comprehensive CFD analysis of the combustion chamber showed that, in contrast to this, small geometrical features influence the mixing process in the combustion chamber and can have an effect on the exit temperature profile. This in turn can reduce the accuracy of the EGT measurement significantly and create measurement errors and misinterpretations of the real engine performance. In order to get insight into the flow topology, a very detailed digital model has been created using scans of the hardware available in the shop. Important geometrical features such as the cooling provisions and swirl creating components have been included in a very detailed manner with an efficient hexahedral mesh. The model includes the HPT vanes and the cooling flow extraction from the secondary cold flow. CFD results have been generated using the flow solver Ansys CFX 17.1, which is able to predict all relevant physical effects such as injection of liquid fuel, evaporation, and combustion of Jet A1 fuel using the Burning-Velocity combustion model. The flow in the combustion chamber shows large natural fluctuations. Subsequently, for each case a transient calculation has been carried out in order to allow an evaluation of the time-averaged flow field. Different geometrical features are investigated to predict the effect of geometry deviations on the exit temperature profile, e.g. the shape and size of the dilution holes. Finally along the example of two CFM56 engines it will be shown how the data obtained by the detailed CFD model is used to optimize work-scoping and maintenance procedures. On the two cases put forward the combination of extended test-cell instrumentation and detailed modeling enabled not only the identification but also the rectification of combustion chamber deviations. This in turn minimized the necessary work, whereas in the past combustion chamber issues often went unnoticed and consequently resulted in extensive additional work.

On the Effects of Aero Boundary Layer Control on Pressure Drag Reduction in Supercavitating Bodies

2005 ◽  
Author(s):  
Yasmin Khakpour ◽  
Miad Yazdani
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Pressure Distribution ◽  
Constant Pressure ◽  
Viscous Drag ◽  
Cavity Surface ◽  
Gradient Flows ◽  
Supercavitating Vehicles ◽  
Pressure Drag ◽  
Layer Control

Supercavitation is known as the way of viscous drag reduction for the projectiles, moving in the liquid phase. In recent works, there is distinct investigation between cavitation flow and momentum transfer far away from the cavity surface. However, it seems that there is strong connection between overall flow and what takes place in the sheet cavity where a constant pressure distribution is assumed. Furthermore as we’ll see, pressure distribution on cavity surface caused due to overall conditions, induct nonaxisymetric forces and they may need to be investigated. Primarily we describe how pressure distribution into the cavity can cause separation of the aero boundary layer. Then we present some approaches by which this probable separation can be controlled. Comparisons of several conditions exhibits that at very low cavitation numbers, constant pressure assumption fails particularly for gradient shaped profiles and separation is probable if the flow is sufficiently turbulent. Air injection into the NATURALLY FORMED supercavity is found as an effective way to delay probable separation and so significant pressure drag reduction is achieved. In addition, the position of injection plays a major role to control the aero boundary layer and it has to be considered. Moreover, electromagnetic forces cause to delay or even prevent separation in high pressure gradient flows and interesting results obtained in this regard shows significant drag reduction in supercavitating vehicles.

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