Blockage Ratio Research Articles

Experimental study to investigate the effects of bridge geometry and flow condition on hydrodynamic forces

Stream-crossing bridges are designed to pass the design flow while maintaining a minimum freeboard; however, flood events are reported as the most frequent cause of bridge failure in the U.S. and around the world. Floodwater exerts significant forces on bridges, shearing and overturning their decks, which may cause them to fail. When a bridge fails, it loses its total or partial serviceability, causing fatalities, delays in emergency transportation and evacuation efforts, and economic losses. An accurate estimation of hydrodynamic forces on a bridge superstructure, therefore, is vital to assess its vulnerability to flooding. The purpose of this study is to investigate the effects of bridge geometry and flow conditions on hydrodynamic forces. A series of experiments on bridge scale models were performed in a laboratory flume to analyze the response of the drag, lift and moment coefficients to bridge geometry (deck width, and girders height and shape) and flow conditions (inundation ratio, proximity ratio, blockage ratio, and Froude number). The experimental results showed that hydrodynamic force and moment coefficients are dependent on the extent of the bridge submergence, Froude number, and proximity of the bridge to the streambed. The relationship between bridge geometry and force coefficients indicated that the geometric features of bridges have a large influence on flow field as well as drag, lift, and moment coefficients.

Experimental Observation of Premixed Methane/Air Flame Propagation in an Obstructed Tube With Increasing Blockage Ratios

Abstract Methane explosion is one of the major hazards in the mechanical industry. In this paper, a series of methane/air premixed combustion experiments were carried out to study the influence of blockage ratio on flame propagation. The blocking ratio (BR) is referred as the cross-sectional area of occlusion divided by the total area. Flame shape and pressure response were measured and analyzed. The results showed that five typical stages were experienced for all configurations except for BR = 0.999, particularly, a diamond-shaped flame and a mushroom-shaped flame front were observed for some lower BRs. The largest length of jet flames was selected to characterize flame–obstacle interaction rose smoothly until BR = 0.9 and then declines rapidly. The flame evolution process was simulated by a power-law flame wrinkling model. Flame behaviors and pressure dynamics for each configuration were investigated, and the maximum flame speed, explosion pressure, and growth rate coincide exactly with the largest length of jet flames in trend. It can be seen that BR was of great significance to flame propagation and BR = 0.9 was a limit or a watershed. In addition, the pressure growth rate was positively correlated with the flame tip speed.

Magnetohydrodynamic mixed convection and entropy generation analysis of Al2O3-water nanofluid past a confined circular cylinder

Numerical simulations are carried out for transient magnetohydrodynamic mixed convective heat transfer of alumina–water nanofluid flow past an isothermal circular cylinder confined in an electrically insulated rectangular duct in the presence of a uniform transverse magnetic field. A control volume method is used to solve the governing equations on a nonuniform Cartesian grid, and the cylinder is imposed using the immersed boundary method. Numerical experiments are performed for a Reynolds number based on the cylinder diameter of ReD=200, blockage ratio of BR=0.2, Richardson numbers of (Ri=−1;0;2), nanoparticle volume fractions of (φ=0.0;0.1;0.2), and Hartmann numbers in the range 0≤Ha≤13. In this work, mean and instantaneous flow and thermal distributions are analyzed graphically, and their corresponding sensitivity to the nanoparticle volume fraction has been determined. Numerical predictions demonstrate the impact of buoyancy and magnetic parameters regarding the spatial development and shedding characteristics of the near wake, and we explore their potential use to selectively excite or suppress vortex shedding, augmentation of heat transfer, and entropy generation minimization in nanofluid flow. The results reported herein indicate that depending on the parametric set, linear and nonlinear flow response to magnetic excitation is observed with bifurcations between different states. The outcome of the study shows that vortex shedding is completely suppressed when a critical value of the Hartmann number is reached, and that the threshold value of the Hartmann number strongly depends on the value of the buoyancy parameter and nanoparticle volume fraction. Based on the entropy distributions, we show that for all values of the nanoparticle volume fraction and in the range of buoyancy and magnetic parameters considered in this work, the entropy generation is dominated by irreversibilities due to heat transfer and the relative contributions of entropy generation due to fluid friction and magnetic effect are not preponderate.

Blockage Effects in Wind Tunnel Tests for Tall Buildings with Surrounding Buildings

To study the blockage effects in wind tunnel tests for tall buildings with surrounding buildings and establish a reasonable calculation method for the blockage ratio, this paper carried out fifty-one test conditions of pressure model wind tunnel tests with three scale ratios. The tests considered the relative location, relative height, and model number of the surrounding buildings to those of the target building by the rigid pressure models. Based on the wind tunnel tests, the blockage effects on the pressure coefficients and drag coefficients were studied in detail. The results showed that the blockage effects were different when the relative positions of the surrounding models to the target model were different, even if the blockage ratio was the same. The blockage effects caused by the surrounding models with unit blockage ratio were usually more significant than those caused by the target pressure-measuring model itself. The existing correction methods for the blockage effects are mainly derived from the wind tunnel tests of an isolated building model. Using existing calculations to evaluate the blockage effect of wind tunnel tests for tall buildings with surrounding buildings may result in obvious deviations. Finally, the concept of the equivalent blockage ratio was proposed, which can be used to calculate the blockage ratio of wind tunnel tests of tall buildings with surrounding buildings. The proposed calculation method of this equivalent blockage ratio can provide a reference for the determination of scale ratios for wind tunnel test models of tall buildings.

Scale Model Experiments and Simulations to Investigate the Effect of Vehicular Blockage on Backlayering Length in Tunnel Fire

This study used model experiments and numerical simulations to investigate the backlayering length of a vehicle-blocked tunnel fire. The experimental setup included two types of obstacles (low obstacles and high obstacles), as well as three configurations: no obstacles, one side with a car obstacle, and two sides with a car obstacle. If there were vehicles on one side of a lane, it would have little effect on the elongation of the backlayer length. When there were vehicles on both sides of a lane, the elongation of the backlayer length was greatly reduced. In addition, the effects of the vehicular blockage ratio and blockage configuration on the properties of the backlayering length were investigated. We created Pattern A, where fire is was in the center, and Pattern B, where fire was on the side of the tunnel. In Pattern A, almost all obstacles could be approximated using the formula. When the vehicle blockage ratio of a single lane was small, an approximation formula for Pattern B was applicable. However, if the distance between stationary vehicles on the upstream side of the fire source was small, the backlayering length could have been longer than in the case with no vehicular blockage.

Effect of a Perforated Polyethylene Material on Propane-Air Explosion in a Confined Space.

In this study, the effect of polyethylene barriers with different blockage ratios on the explosion behavior of a propane–air premixed gas in a confined space is investigated. The maximum explosion pressure (Pmax), the deflagration index (KG), and the flame propagation process of the propane–air premixed gas with different barrier thicknesses are examined by using a horizontal closed tube with a length of 0.5 m and a diameter of 0.1 m and a high-speed camera. The atmospheric pressure and temperature of the premixed gas were 101.3 kPa and 18 °C, respectively. Based on the Canny operator, the position of the flame front at different times and the shape of the barriers before and after the explosion are determined, and the propagation speed of the premixed flame and the deformation rate of the barriers are obtained. The results indicate that the barriers change the flow field structure of the unburned gas and increase the folding degree of the flame front. With the increase in the blockage ratio, the explosion of a premixed system becomes more rapid and violent. Under the action of Rayleigh–Taylor instability, the variation in the flame propagation speed induces a change in the tube pressure. In addition, the deformation of a barrier causes a change in the maximum explosion pressure. The greater the deformation ratio of the barrier after the explosion, the larger the maximum explosion pressure.

Particle image velocimetry measurements of turbulent flows in rotating square ribbed ducts

This paper investigates the flow characteristics along a ribbed square duct using time-resolved particle image velocimetry. The Reynolds number, defined by the main flow velocity (1.82 m/s) and the hydraulic diameter (80 mm), is 10 000. The rotation numbers are 0, 0.13, 0.26, 0.39, and 0.52. The blockage and aspect ratios of the ribbed square duct are 0.1 and 1, respectively. As the rotation number increases, the recirculation zone on the suction side becomes larger, and the reattachment point moves downstream. The opposite behavior is observed on the pressure side, and this trend develops along the duct. Furthermore, the flow characteristics between different pairs of ribs along the duct vary greatly at the same rotation number. For the downstream ribs, the main stream velocity pattern is deflected more to the pressure side, where both the recirculation zone and the extreme region of Reynolds shear stress are larger than on the suction side.

The rise and fall of banana puree: Non-Newtonian annular wave cycle in transonic self-pulsating flow

We reveal mechanisms driving pre-filming wave formation of the non-Newtonian banana puree inside a twin-fluid atomizer at a steam–puree mass ratio of 2.7%. Waves with a high blockage ratio form periodically at a frequency of 1000 Hz, where the collapse of one wave corresponds to the formation of another (i.e., no wave train). Wave formation and collapse occur at very regular intervals, while instabilities result in distinctly unique waves each cycle. The average wave angle and wavelength are 50° and 0.7 nozzle diameters, respectively. Kelvin–Helmholtz instability (KHI) dominates during wave formation, while pressure effects dominate during wave collapse. An annular injection of the puree into the steam channel provides a wave pool, allowing KHI to deform the surface; then, steam shear and acceleration from decreased flow area lift the newly formed wave. The onset of flow separation appears to occur as the waves' rounded geometry transitions to a more pointed shape. Steam compression caused by wave sheltering increases pressure and temperature on the windward side of the wave, forcing both pressure and temperature to cycle with wave frequency. Wave growth peaks at the nozzle exit, at which point the pressure build-up overcomes inertia and surface tension to collapse and disintegrate the wave. Truncation of wave life by pressure build-up and shear-induced puree viscosity reduction is a prominent feature of the system, and steam turbulence does not contribute significantly to wave formation. The wave birth-death process creates bulk system pulsation, which, in turn, affects wave formation.

막힘률에 따른 저선회 화염 동역학에 대한 실험적 연구

The influence of the blockage ratio on low-swirl flame dynamics was experimentally investigated in a lean-premixed combustor. Here we test five different swirl injectors, one with high swirl and four with low swirl, all with different blockage ratios (β). We analyze a large experimental dataset of self-excited instability measurements, and show that instability amplitudes for the case of β = 0.75 tend to be remarkably attenuated. This is attributed to the development of out-of-phase modulations between the jet-stabilized flame in the inner section and the swirl-stabilized flame in the outer section.

Explosion behavior of non-uniform methane/air mixture in an obstructed duct with different blockage ratios

An experimental investigation on explosion behavior of non-uniform methane/air explosion in obstructed duct with different blockage ratios is conducted. The methane/air mixture that the methane concentration decreases from top to bottom and from ignition end to opposite end of duct is tested. The results show that the vertical concentration gradient of methane upstream along the obstacle increases with blockage ratio. After ignition, the flame speed and overpressure increase exponentially when the flame propagates with a finger-liked shape. In the poorly mixed methane/air, the flame speed and overpressure reduce with the appearance of pronounced triple flame. The flame in duct without obstacle propagates with triple shape until it approaches the vent. In the obstructed duct, the flame speed increases again after the flame passes the obstacle and then the triple flame disappears as the flame becomes turbulent. In the more evenly mixed methane/air, the flame speed decreases with the disappearance of finger shaped flame. The flame speed decreases continuously in duct without obstacle but increases again when the flame passes the obstacle in obstructed duct, in which an incomplete mushroom-shape flame forms downstream the obstacle. Generally, both the flame speed and overpressure are larger in methane/air that mixes more fully.

Influence of slot profiles on the characteristics of jets

PurposeThe purpose of this research is to study and investigate the flow control of 0.8 Mach jet using three tab configurations. The tabs with the slots will eventually lead to generation of vortices and thus enhances the mixing characteristics.Design/methodology/approachThe jet flow control is achieved by the usage of three tabs, namely, Tab A, Tab B and Tab C that are placed at the exit plane of the convergent nozzle at 180 degrees apart. Three tabs with different slot profile are designed with the same constant blockage ratio of 7.3%. The tabs produce vortices of varying sizes that directly influence and modify the jet structure, thereby enhancing the efficiency in mass entrainment and mixing. The tabs are studied numerically first and then are compared with the results of the experiments.FindingsThe results are compared with that of the results of the uncontrolled jet. For Mach 0.8 jet, Tab C is found to reduce the core length and gives reduction of 90.23%, in comparison to Tab A and Tab B, which provides 84.1% and 87.79%, respectively. The results of numerical are then compared with the centerline results obtained via experiments. With the engagement of Tabs A, B and C, the jet structure is seen to have been modified at Mach 0.8 with Tab C performing better.Practical implicationsThe tabs are a passive control device that can be practically enabled in the aircraft nozzles to control the flow and even suppress the noise emanated by the jet. Tabs can be effectively used for better thrust vector control and assist in jet noise suppression. Thus, this study on tabs and its uses are important and essential in aerospace technology.Originality/valueThis particular study on mechanical slotted tabs is innovatively carried out by designing the tabs in such a way that one such has not been designed before. The slots run through the adjacent sides of the tabs which is a novelty in itself, whereas perforations made only through the opposite sides of the tabs are studied by various researchers till now. The slots in the adjacent faces modify the flow physics in such a way that it enhances mixing by the creation of turbulence because of the interaction between the main stream and the secondary jet exactly at the core. So far, such slots and profiles are not investigated. By the usage of such tabs, the flow to mix faster is much closer to the core of the jet by creating mixed size vortices and thus has higher efficiency.

The Blockage Ratio Effect to The Spray Performances

Nozzle sprays are used in wide range of application. The used of nozzle application is depend on the spray characteristics, by which to suit the particular application. This project studies the effect of the air blockage ratio to the spray characteristics. This research conducted into two part which are experimental and simulation section. The experimental was conducted by using particle image velocimetry (PIV) method, and ANSYS software was used as tools for simulation section. There are two nozzles were tested at 1 bar pressure of water and air. Nozzle A (with blockage ratio 0.316) and nozzle B (blockage ratio 1.000). Both of the sprays performances generated by the nozzles was examined at 9 cm vertical line from 8 cm of the nozzle orifice. The validation result provided in the detailed analysis shows that the trend of graph velocity versus distance gives the good agreement within simulation and experiment. From result, nozzle A generated a wider spray angle and higher water droplet velocity which are 31.41 degree and 37.317 m/s compared to nozzle B which has produced 27.13 degree of spray penetration angle and 16.49 m/s water droplet velocity. As a conclusion, blockage ratio has affected the spray system by increasing the velocity of air inside the spray system. This is happened at a condition of 1 bar air pressure.

Study on the Influence of Vent Shape and Blockage Ratio on the Premixed Gas Explosion in the Chamber with a Small Aspect Ratio.

Given the current situation of deflagration caused by gas leakage for domestic use and the study of the single shape of the vent, the differential change law of vent parameters on the small aspect ratio of the chamber explosion flame evolution and explosion overpressure and other effects were experimentally investigated. Based on the theory of geometric similarity, the experimental platform of a small length–diameter ratio explosion chamber was designed and built, and the premixed gas explosion experiment was carried out by changing the shape (square and rectangle) and blockage ratio (0.1, 0.3, 0.5, 0.7, and 0.9). The explosion flame structure, flame front position, flame propagation speed, explosion pressure waveform, overpressure peak value, and so on were tested and analyzed. The results showed that the blockage ratio had the most significant effect on flame propagation and explosion flame evolution. With the increase of blockage ratio, the stretching degree of the flame became more and more obvious, the flame front became sharper and sharper, and the sharp flame changed from the lower part to the upper part. The position of the flame front increased rapidly, and the steepness and peak value of explosion overpressure became larger. The oscillation of the flame propagation velocity was more violent after the turn, and the speed of propagation to the outside of the chamber gradually accelerated. In the same blockage ratio, there was a difference in the time point at which the flame propagation velocity turned under the rectangular and square shape of the vent. In blockage ratios of 0.1, 0.3, 0.5, and 0.9, the peak overpressure reduction under the shape of the blast square relative to the rectangle was 41.3, 47.9, 1.03, and 27.6%. This indicated that the explosion relief effect of the square was better than that of a rectangle. The research results can provide a reference and basis for the reasonable deployment of explosion venting and explosion decompression work.

Influence of cavity inclination on mixed convection in a double-sided lid-driven cavity with a centrally inserted hot porous block

A numerical investigation is made to understand the influence of seven distinct cavity inclination angles (α = 0°, 15°, 30°, 45°, 60°, 75° and 90°) on the fluid flow behaviour during mixed convection in a double-sided lid-driven cavity for varied Richardson numbers (0.01≤Ri≤100). A hot porous square block with a blockage ratio of 0.25 is inserted at the cavity centre. We employ the multiple-relaxation-time lattice Boltzmann technique, which incorporates the Brinkman-Forchheimer-extended Darcy model for simulating flow through the permeable structure at different Darcy numbers (10−2≤Da≤ 10−6). The validation of the present developed code provides reasonable agreement with the previously reported findings acquired using conventional CFD approaches. It is noticed from the results that the cavity inclination angles provide a substantial impact on the generation of entropy and the rate of heat transfer. Furthermore, the findings reveal that the values of Ri and Da influence the optimal energy-efficient condition for a flow configuration.

Flow over a confined mounted fence at low and moderate Reynolds number: A numerical study

Direct numerical simulations of a flow over a wall mounted fence confined by two parallel walls were conducted at low and transitional Reynolds number (50⩽ReD⩽2000) for blockage ratios ranging from 0.25 (low blockage) to 0.9 (high blockage). A primary recirculation bubble forms downstream of the fence and the length of this recirculation region increased with Reynolds numbers. A secondary recirculation bubble appeared on the opposite wall to the mounted fence for the laminar cases with higher blockage ratios at sufficiently large Reynolds number. The separation and reattachment locations were documented and compared with numerical and experimental data. The length of the primary recirculation bubble in current simulations are consistent with the literature while the comparison of the secondary recirculation bubble with experimental data had limited agreement. This secondary recirculation bubble disappeared for the cases at transitional Reynolds number. Instead, the strong primary recirculation bubble induced a corner eddy at the rear of the fence. ‘Packets’ of cross stream velocity fluctuations were observed as the initially 2D, steady, laminar shear layer breakdowns to a 3D turbulent flow. The space–time diagram also showed ripple-like fluctuations of the shear layer further downstream of the fence with a single distinct peak observed in the streamwise and cross flow velocity fluctuations spectra. This peak in the spectra can be predicted by linear stability analysis of a mixing layer (Yasuo et al., 1986). In the near wake, scale-like features were observed while patches of fluctuations of a longer timescale were noted in the recirculation region.

Effect of obstacle location on explosion dynamics of premixed H2/CO/air mixtures in a closed duct

An experimental study was presented to investigate the effect of obstacle location (OL) on explosion dynamics of premixed H2/CO/air mixtures. A fence-type obstacle providing the blockage ratio of 0.5 was mounted in the closed duct, and the distance from the ignition end increased from 100 mm to 600 mm. Therefore, the effect of the obstacle on flame exponential acceleration stage, flame deceleration stage, and tulip flame stage had been comprehensively discussed. When OL ≤ 400 mm, the turbulent finger-shaped flame front will invert into the tulip shape after the flame propagates through the obstacle channel. The competition between the flamelets’ backward movements induced by the vortex motion and forward movement induced by the squish flow causes the turbulent finger-shaped flame front’s inversion. The pressure dynamics are discussed in conjunction with flame tip dynamics. The prominent flame deformation and oscillation after the tulip flame is caused by the interaction of flame and pressure waves. However, the pressure waves make no difference on the finger-shaped flame front inversion. This indicates that the flame front inversion after the obstacle is a pure hydrodynamic phenomenon. What’s more, for a given hydrogen volume fraction, the flame duration time first decreases and then decreases with obstacle location, the maximum flame tip speed and the maximum overpressure first increases and then decreases with obstacle location, and the maximum explosion severity occurs at OL = 400 mm.

Effect of opening blockage ratio on the characteristics of methane/air explosion suppressed by porous media

Gas explosion is a common serious accident in underground coal mines and industrial production processes. Porous media, due to its special cellular structure, has a significant effect on stopping the propagation of pressure and flame, which can effectively reduce the explosion hazard. In this study, the explosion suppression effect of Fe-Ni and Cu foams with different pore sizes (20 and 40 holes pores per inch (ppi)) was experimentally investigated and comparatively analyzed at opening blockage ratios (OBR) equal to 0.36, 0.64 and 0.84, respectively. The results demonstrate that Fe-Ni foam with 20ppi quenches the flame only under the OBR of 0.84, which indicates that the larger the OBR is, the better the explosion suppression effect is. However, under the OBR of 0.64, the porous media achieve an enhanced quenching efficiency and the shortest quenching time. In addition, when the vent area is relatively large, the obstacle effect of porous media is stronger than its pressure absorption capacity, thus leading to an increased pressure in the explosion area. The lowest peak overpressure attenuation rate, − 25.9%, is observed for 40ppi Fe-Ni foam under the OBR of 0.36. In general, the OBR is positively correlated with the depressurization capacity. Among all the cases used in this study, the 20ppi Cu foam boasts the highest upstream and downstream peak overpressure attenuation rates under three OBRs, 0.86%, and 6.33%, respectively.

Effect of the Nozzle Geometry on Flow Field and Heat Transfer in Annular Jet Impingement

The effects of nozzle shape modifications on the flow phenomena and heat transfer characteristics in annular jet impingement are investigated numerically. The numerical simulations are conducted applying the shear stress transport (SST) k−ω model in the ANSYS CFX. Two modified nozzles: the converging nozzle and the diverging nozzle, are investigated in this study, and the straight nozzle serves as the base case. The geometric parameters and settings are based on an annular jet ejected from an axial fan used for electronic cooling: the Reynolds number Re= 20,000 and the blockage ratio Br=0.35 in the computation, and the target plate is placed at three representative separation distances: H=0.5,2, and 4. Compared with the base nozzle, the converging nozzle can accelerate the cooling flow and promote turbulence to enhance local and overall heat transfer (about 20%) over the target surface. In addition, the converging nozzle reduces the sizes of the recirculation zones, and this promotes the convective heat transfer transport near the axis. The diverging nozzle experiences a similar flow pattern and thermal field as the base nozzle, while the diverging nozzle achieves a slightly lower heat transfer with a pronounced pressure drop reduction. In addition, given that the value of the Nusselt number over the target plate is dependent on the Reynolds number, the simulations are also performed at Re=5000 and 40,000 to establish the correlations between the Nusselt number and the Reynolds number as Nu∝Rem. The value of m varies depending on the nozzle shapes and the separation distances.

Inertial migration of a neutrally buoyant oblate spheroid in three-dimensional square duct poiseuille flows

In this paper, the inertial migration of a single neutrally buoyant oblate spheroid in a square duct is investigated by multiple-relaxation-time lattice Boltzmann method. The spheroid’s aspect ratio AR=a/b=1/2, where a and b are the polar and equatorial radii of the spheroid, respectively, Reynolds number Re=UmH/ν=80 with Um, H and ν being the maximum velocity in the duct without the particle, height of the duct and the kinematic viscosity, respectively, and a blockage ratio 2b/H=0.277 is chosen to study the effects of initial position and initial orientation on the particle’s motion in detail. Our results show that the lateral trajectory and final motion, to some extent, depend on the spheroid’s initial position and orientation. In addition to the general log-rolling (LR) mode, which was previously reported by Lashgari et al. (2017), the spheroid can also exhibit a tumbling (TU) mode, where its polar axis rotates in the central streamwise–wall-normal plane, and an inclined log-rolling (ILR) mode, where it rotates in the diagonal plane with the polar axis being perpendicular to the plane, when its initial position and orientation are well specified. With the Reynolds number increased to 160, the ILR mode disappears while the TU and LR modes persist. If AR decreases to 1/3 while keeping the particle’s volume fixed, all three modes persist at Re=80, and the particle migrates closer to the duct center at the final equilibrium state with decreasing AR for all three different modes.

A comparative study of gaseous fuel flame characteristics for different bluff body geometries

Flame stabilization by a bluff-body is commonly used in many combustion applications to improve mixture characteristics, enhance flame stability and assist in combustion control. The main objectives of the present experimental work are concerned with studying the flame stabilization and combustion characteristics of Liquefied Petroleum Gas (LPG) with different bluff body shapes and sizes. An experimental test rig that consists of a gaseous fuel line, compressed air line, mixing chamber and burner is designed and constructed. Different bluff body shapes such as disc, cone, V-gutter, horizontal and vertical cylinders are used. The effects of different Blockage Ratios (B.R.) of 0.25, 0.35, 0.45, and 0.55 are studied at a constant equivalence ratio (Փ) of 1.85 for different bluff body shapes. The blowoff limits, temperature distributions, flame shapes, exhaust species concentrations and visible flame length are experimentally measured and discussed. The results indicated that increasing the blockage ratio leads to increasing the maximum flame temperature, increasing the flame diameter, and decreasing the flame length for all bluff body shapes. The centerline axial NO concentration has its peak values coincide with the maximum centerline axial temperatures. The flame using bluff body cone is more stable than using other bluff body shapes i.e., it has wide flammability limits or a wide range of operating conditions.