Plenum Chamber Research Articles

Advanced Modeling of Hydrogen Turbines Using Generalized Conformable Calculus

This article addresses critical challenges in the transition to clean energy sources by highlighting the importance of advanced mathematical modeling and computational techniques in turbine design and operation. Specifically, we extend and generalize the work of Camporeale to advance the modeling of hydrogen turbine systems. By utilizing conformable calculus, we develop dynamic equations that analyze key aspects of turbine performance, including temperature variations in turbine blades, angular velocities of rotating shafts, and mass--energy balances within the plenum and combustion chamber. Furthermore, we incorporate Kirchhoff's equation in its generalized conformable integral form, enhancing the precision of energy balance calculations and improving the representation of heat transfer processes in the combustion chamber. This methodology introduces novel perspectives in hydrogen turbine research, contributing to the advancement of sustainable and efficient technologies. Our comprehensive approach aims to provide more accurate and efficient predictions of turbine behavior, thereby impacting the design and optimization of hydrogen-based clean energy systems.

Modeling and performance estimation for L-shaped OWC wave energy converters with a theoretical correction for spring-like air compressibility

The investigation of Oscillating Water Columns (OWC) has gained significant attention in recent years thanks to their resilient structural design, allowing them to withstand harsh environmental conditions. This study focuses on the L-shaped OWC (L-OWC) due to its excellent energy capture efficiency. It should be noted that air compressibility plays a significant role in the plenum chamber of the OWC, especially at full scale. The present paper proposes a scaling-rematched approach, facilitating the evaluation of hydrodynamic coefficients and the performance estimation with a theoretical correction for the unmatched scaling problem of spring-like air compressibility. The methodology is applied successfully to a model-scale L-OWC design, employing three-dimensional, incompressible-flow simulations combined with an impeller model. The present study reveals the hydrodynamic characteristics (advantages) of the L-OWC: small fluid damping coefficient and large added mass, and hence the possibility that the spring-like air compressibility can be used to raise the efficiency of power capturing. Furthermore, there exists an interval where the air compressibility has a positive effect on the performance, not only having a significantly longer span than that of the conventional OWC but also much more directly matching the period range of high energy potential found in the wave climate of Northeastern Taiwan waters.

On the enhancement of acceptable blockage of open jet wind tunnel by employing modifications based on concepts of boundary layer and jet flow for testing of aero-rotors

The conventional closed and open jet tunnels suffer from various adverse blockage effects that alter the flow conditions generating erroneous results when larger than allowable blockage models are tested. The maximum acceptable blockage is limited to 25 % for an open jet tunnel. The physics behind the inferior blockage capacity and their redressal is investigated. Hitherto, numerical models are developed to rectify the blockage troubles that introduce an additional complex case-based mathematical modeling to reckoning the results. In the current paper novel approach to redesigning the tunnel to solve blockage troubles is investigated that facilitates evading of mathematical techniques and securing accurate results straightforwardly. A hypothetical design incorporating the remedies is proposed, capable of conditioning the flow in a manner that debilitates the adverse effects of solid blockage, wake blockage, jet expansion, etc. The hypothesis is theoretically expounded by the boundary layer and jet flow phenomenon. The modified blower-type open jet wind tunnel constitutes a centrifugal blower, long inlet duct, plenum chamber around the test section, and collector. The modified wind tunnel is tested through experiments executed on four different-sized Savonius rotors creating 10 %, 30 %, 50 %, and 60 % blockage. The static pressure along the contours of the blades of rotors is obtained. The experimental results are juxtaposed with CFD results carried out at free-wind boundary conditions and standard classic experimental results performed in conventional wind tunnel at 11 % blockage. A blockage enhancement of 25 % is achieved by the approach of modification in the design of a conventional open jet wind tunnel.

Dependence of Pressure Characteristics of Pressurized Pulse Water Jet Chamber on Nozzle Diameter

The nozzle is the key element of the water jet generator for energy conversion. In order to explore the influence of the nozzle diameter on the pressure characteristics of the supercharged pulsed water jet plenum chamber, a supercharged pulsed water jet pressure acquisition system was established, and the equations of motion and theoretical pressurization ratio equations of the supercharged pulsed water jet generator were established. The pressurization chamber pressure acquisition experiments under different nozzle diameters were carried out. The research results show that the pressurized pulsed water jet generator has a critical nozzle diameter of 0.6 mm. When the nozzle diameter is less than the critical diameter, the pressure in the boost chamber is equal to the product of the driving pressure and the boost ratio. As the nozzle changes, there is no significant change in the peak pressure and frequency of the boost chamber. When the nozzle diameter is greater than the critical diameter, there is a non-linear relationship between the boost chamber pressure and the driving pressure. As the nozzle diameter gradually increases, the actual boost ratio gradually decreases, and the peak pressure of the boost chamber further decreases. The nozzle diameter can no longer provide a load for the establishment of fluid pressure in the boost chamber. The results of this research provide a research basis for further controlling the pressure characteristics of the boost pulse water jet.

Towards accurate modeling of vibration in CFD-DEM simulations of vibrated gas-fluidized beds without using a moving mesh

Vibrated gas-fluidized beds are widely used industrially, and two main methods exist to simulate them computationally: (i) in a moving reference frame by oscillating gravity and (ii) in a stationary reference frame by moving the distributor. Further, it is unclear whether gas flow in the plenum chamber of a vibrated fluidized bed should be modeled as constant or oscillating. Here, we challenge the accuracy of different potential modeling methods by comparing with experimental results of structured bubbling because these results are deterministic, avoiding the need for comparing via statistically averaged quantities. Results show that modeling a moving distributor and moving sidewalls as physically accurately as possible is important, and modeling the system in the moving reference frame is less accurate than in the stationary reference frame, due to subtle differences. Further, it is more accurate to model the gas flow as constant rather than oscillatory in the plenum chamber.

Laminar to turbulent transitions of pipe flows by resonances of natural frequencies of components of test sections

This investigation analyses special papers and doctoral theses that treat transitions of pipe flows as a resonance phenomenon of wave frequencies. These frequencies are natural frequencies of pipe flows, of components of the test section and of vortex ring formations. Resonance conditions are derived that show how the critical Reynolds number, Rec , depends on the volume of the plenum chamber, the pipe diameter, the pipe length, etc. The derived resonance relations were verified experimentally using the experimental data of the third author, yielding R e c ∼ 1 / V ple , R e c ∼ 1 / ( L D ) and other interesting results. These findings suggest that the laminar-to-turbulent transition has various modes and transitive dependences. To understand this fully, it is necessary to take all components of the test section involved into account. The test section considered in this paper consists of a mass flow controller to supply the airflow and a plenum chamber, followed by the actual pipe of interest. It is shown that all the components can contribute to the measured value of the critical Reynolds number of pipe flow transition.

A Novel Design of a Pre-separation Panel Structure to Protect Against the Impact of an Explosion in an Aircraft Plenum Chamber

A Novel Design of a Pre-separation Panel Structure to Protect Against the Impact of an Explosion in an Aircraft Plenum Chamber

Performance Characteristics of a Rotating Detonation Combustor Exiting Into a Pressurized Plenum to Simulate Gas Turbine Inlet

Abstract The present study aims to experimentally characterize the performance of a rotating detonation combustion (RDC) system integrated with a pressurized downstream plenum to simulate the high-pressure inlet conditions of power-generating gas turbines. A thorough understanding of the operational behavior including wave mode behavior, static pressure profile along the combustor length, and dynamic features of pressure fluctuations is crucial for successful integration of RDC with the turbine. In this study, two RDC configurations are investigated, RDC with a constant area annulus and RDC with a converging nozzle. In both cases, the RDC flow exited into a plenum chamber kept at pressures varying from 155 kPa to 330 kPa. RDC was operated on methane and oxygen-enriched air to represent reactants used in land-based power generation. Experiments were conducted for the two RDCs configurations operated at three reactant mass flow rates (0.23, 0.32, and 0.46 kg/s). The RDC performance is characterized by time-averaged static pressure measurements, and wave velocity determined by ionization probes. In addition, dynamic pressure measurements were recorded both inside and near the exit of RDC channel to investigate wave interactions between RDC and downstream plenum. Results show that the RDC with the converging nozzle achieved superior performance while minimizing detrimental interactions with the reflected shock and/or acoustic waves from the downstream plenum.

On the Hybrid Modelling of Rigid Sonic Crystal Embedded in Plenum Chamber at Low Frequencies Using the Effective Medium Approach and Finite Element Method

This study explores the application of homogenization schemes in modelling acoustic wave propagation in a finite array of circular scatterers embedded into a 2D cavity. The cavity is integrated into the 2D waveguide attached to the cavity inlet and outlet. Square-lattice sonic crystal (SC), composed of rigid and radially symmetric circular cylinders, is used to represent the finite array in this study. The model is aimed at informing the novel designs of plenum windows with superior soundproofing performance. The sound transmission performance is analysed with hybrid numerical simulation using the Finite Element Method (FEM) and homogenization scheme. A theoretical homogenization method based on the Effective Medium Approach (EMA) is reviewed and implemented on the modelling of the SC array inside the cavity at low frequencies and then implemented in FEM. Comparison of the transmission loss (TL) reveals a high degree of matching between settings with and without homogenization at low-frequency range. It is observed that performance of the hybrid model maintains a high degree of matching provided the cavity modes are dominated by a single characteristic scale in the low frequency. This includes the case of a narrow plenum chamber with only a single cylinder placed inside the cavity with a width of one lattice constant. This homogenization method is proven to be more computationally efficient in FEM compared to the modelling of exact geometry of the problem.

Experimental Study on the Improvement of Film Cooling Effectiveness of Various Modified Configurations Based on a Fan-Shaped Film Cooling Hole on an Endwall

Several studies have previously been conducted to improve the cooling performance of film cooling. However, most of the research has conducted experiments with film cooling holes on flat plates, and thus, the results of these studies do not encompass the influence of the complex mainstream behavior within the turbine passage on film cooling. In this study, three different film cooling hole configurations were installed on the endwall of a turbine linear cascade to measure adiabatic film cooling effectiveness and evaluate cooling performance. The film cooling holes compared in the experiment for film cooling effectiveness were a 7-7-7 fan-shaped hole (Baseline), a Baseline with a double-step structure at the hole exit (Staircase), and a Baseline with an additional expanded passage at the hole leading edge (Compound Expansion). A total of nine holes were manufactured on the turbine endwall to assess film cooling performance, as various factors, such as mainstream acceleration, secondary flow within the turbine passage, and so on, can influence film cooling. Adiabatic film cooling effectiveness was measured using the pressure-sensitive paint (PSP) technique. Mass flow ratios ranging from 0.25% to 1.25% of the mass flow rate of a single turbine passage were supplied to the plenum chamber within the test rig. As a result, all experimental results confirmed the impact of secondary flow within the turbine passage on film cooling. In the case of the Staircase, it exhibits an overall cooling trend similar to the Baseline. It shows small cooling performance degradation compared with Baseline due to lift-off, and its double-step structure laterally expanding results in better cooling performance at high mass flow ratio (MFR) conditions. For the Compound Expansion, at low MFR, the momentum of the coolant is lower compared with other configurations, leading to lower cooling performance due to the influence of secondary flow. However, at high MFR, the Compound Expansion provides wider protection compared with other hole geometries and shows high cooling performance.

Experimental and numerical study of a natural convection indirect solar dryer with PCM tubes: Dynamic, thermal and nutritional quality analysis

A natural convection solar dryer was investigated in this paper with a storage unit in the form of copper tubes filled with Paraffin wax as a PCM, experimentally and numerically using the ANSYS Fluent software. The storage unit was placed in a side-mounted plenum chamber for air uniformity and heat recovery. The validations made for the drying chamber’s temperature with and without storage, the outlet air temperature, and velocity of the SAH, show good accordance with the experimental results, which promote the use of this method in investigating the solar dryer numerically. The drying of orange slices in different modes were studied; open sun drying, in a solar dryer with and without PCM. The drying time required to reduce the moisture content from 81.19% (wb) to 19% (wb) was respectively 216 h, 144 h, and 168 h. In terms of the quality of orange slices, the open sun drying showed the poorest quality in terms of color, texture, shape, and odor. However, all these properties were enhanced with the solar dryer, particularly with the use of PCM tubes. The most valuable nutritional value of oranges is vitamin C, which was measured per slice in all mentioned cases. One fresh orange slice contains 11.34 mg of vitamin C, while it contains 7.77 mg, 7.34 mg, and 5.99 mg in the drying cases with and without PCM as well as in open sun drying respectively.

Nusselt Number Distribution Due to Supersonic Flow Impingement and Confinement

When a missile is launched from a canister, the impingement of the exhaust Bases on the plenum chamber creates a complex, viscous/shock interaction flow field. In order to study the rocket plume heat transfer effects on the closed and open plenum chambers, static rocket motor firings are carried out. Static tests are conducted in a small-scale rocket motor loaded with a typical nitramine propellant to produce a nozzle exit Mach number of 3. This supersonic jet is made to interact with the plenum chamber having closed and open sides. The distance between the nozzle exit and the plenum chamber back plate is varied from 6.3 to 9.6 times the nozzle exit diameter for the closed plenum chamber and 5.9 to 9.4 times the nozzle exit diameter for the open plenum chamber. In the plenum chamber, the heat flux has been measured using slug type heat flux gauges mounted at different locations. The temperature - time data are analyzed to obtain an insight into the flow field in the plenum chamber. Thirteen static tests are carried out to obtain the effect of axial distance between the nozzle exit and the plenum chamber back plate, and stagnation pressure in the rocket motor on the local heat transfer, characterized by Nusselt number in the closed and open plenum chambers.

Design and Numerical Simulation of the Performance of Acoustic Plenum Chamber of a Marine Gas Turbine Air Supply System

In the present work, an approach to obtain a design method for the size of the plenum chamber cross-section of a marine gas turbine air supply system has been investigated. Flow in ducts makes noise which is very high in the turbine inlet part because of the large amount of flow. Therefore, this phenomenon should be considered in the design process. A suitable approach to design the duct is proposed (considering acoustic and aerodynamic performance at the same time). In this method, an air supply channel system of the marine gas turbine has been categorized into three sections according to the requirements of the aerodynamic and acoustic; inlet, plenum chamber, and outlet channels with circular cross-sections. The geometrical dimensions of inlet and outlet channels have been determined using the plane waves theory about a channel, in which the effects of flow is ignored. Space limitations of battleships at the dominant frequency have been considered. Then, the optimized size of the mid-channel section, in terms of both aerodynamic and acoustic requirements, using numerical methods and regarding the effects of flow has been calculated. Various 3D turbulent flows inside the plenum chamber have been considered, in which large eddy simulation turbulence model is utilized. Ffowcs, Williams and Hawkings models are used for the sound propagation process based on the Lighthill integral equation. The validity of the simulation has been checked by comparing results (sound pressure level) with experimental data obtained from a chamber. The comparison revealed the acceptable errors for a variety of frequencies. The results disclosed that the performance of channel system aerodynamic decreased when the fraction of plenum chamber cross-section to inlet/outlet channel cross-section increased. With an increase in the cross-section size at first Acoustic performance is improved and then worsen. Six different cases of marine gas turbine air supply system configurations have been presented, in which the limitation of the battleship space is considered. Examining and comparing the acoustic performance of different cases of the air supply channel system, it was found that the amount of sound pressure level, around the air supply channel system, and the high-pressure sound area can move along the air supply channel system. Additionally, deviations from plane waves considering the effects of flow have been inspected in all cases. The reason for this deviation is the effects of the airflow through the channel system and quadrupole sources in the production of sound in the channel system, which causes higher modes.

Design and evaluation of a hybrid solar dryer for postharvesting processing of parchment coffee

Due to the extended drying time open-sun and solar drying of coffee procedures undergo, the development of microorganisms, mycotoxins and molds threaten the product. Alternatives such as mechanical dryers are available, nevertheless, their running costs and setups are usually expensive and unaffordable for small-scale coffee growers. Therefore, this research aimed to design, build and evaluate a hybrid solar dryer which mixes solar and mechanical drying principles. It uses a traditional solar tunnel-type dryer as a base featuring a biomass burner which uses coffee trunks left from the yearly crop renovation as biofuel. A heat exchanger heats the drying air, afterwards blown into a plenum chamber that homogenizes the air's static pressure before crossing the coffee bed, ensuring an even moisture removal. Also, the hybrid unit includes a photovoltaic system to obtain a fully self-sufficient drying unit. The newly developed dryer was tested under three different configurations: Solar and mechanical day and night (C1), solar during the day and mechanical during the night (C2) and fully solar with non-mechanical aid (C3). The results displayed a notable drying time reduction in the three evaluated configurations: C1 reduced the drying time by 70.47%, C2 by 45.75% and C3 by 21.5%. Also, the predictive model for different plenum chamber heights was obtained through computational fluid dynamics simulations, where the ideal height was 0.25 m. A biomass consumption of 1.9 kg h−1 was registered. Also improved temperature and relative humidity profiles were achieved. Its design easily adapts to the existing tunnel and parabolic-type solar dryers.

Validation of numerical simulations for investigating flow control in hypersonic inlets

Various flow control devices have been conceived for hypersonic inlets to suppress the inlet unstart and reduce the total pressure loss over the wide range of operating conditions of hypersonic systems. In particular, bleed systems that remove the low-momentum portion of the flow have drawn attention because they effectively reduce shock-induced flow separation and suppress inlet unstart. Numerical simulations are crucial for investigating the effectiveness of different bleed configurations in hypersonic inlets during the design phase. However, the flow structure in these inlets and the effect of the bleed on the flow are challenging to predict due to complicated factors such as shock-wave/boundary-layer interactions and compressibility effects. Moreover, since the boundary conditions, turbulence model, and turbulence corrections affect the numerical results, the most appropriate model can be difficult to determine. Therefore, a numerical solver was developed and evaluated on a series of validation cases with available experimental data to establish the fidelity of the numerical simulations. Seven validation cases, ranging from an elementary configuration involving a flat plate to a complex configuration involving a flat plate with a porous bleed and plenum chamber, were investigated. The flat plate flow numerical results, including the turbulent boundary layer and shock-wave/laminar boundary-layer interactions, were consistent with previous experimental and numerical results. However, in the hypersonic inlet cases, the actual physical phenomena could not be represented without considering compressibility and streamline curvature effects, which depend on the hypersonic inlet configuration. Thus, the effects of turbulence corrections on the numerical results of various hypersonic inlet configurations were examined. For cases with rapid expansion near the inlet throat or inlets with curved walls, compressibility or rotation/curvature corrections were necessary to accurately capture the size of the recirculation zone and reproduce the wall pressure data and shock structure along the flow path. However, for bleed flows on flat plates, the simulations were accurate without applying turbulence corrections. Thus, these turbulence corrections should be applied only when rapid expansion occurs or the wall near the shock-induced separation zone is curved. This paper provides the best practice appropriate for various supersonic, hypersonic flow cases, and can be utilized in future numerical studies on hypersonic inlet boundary layer control.

Unsteady characteristics of pressure and swirl distortion in helicopter intake: A lattice Boltzmann method approach

The present paper focuses on the analysis of the unsteady characteristics of pressure and swirl distortion and their relationship inside a complex air intake, including a plenum chamber, using Large-Eddy Simulation based on the lattice Boltzmann method (LBM). The steady-state analysis of the pressure field and swirl angle in the Aerodynamic Interface Plane (AIP) shows a complex pressure and swirl distortion pattern, as well as a high level of unsteadiness. Additionally, two vortical structures with equal intensity located on the top and bottom sides of the AIP plane were identified. The unsteady pressure distortion analysis highlighted fluctuations between two positions of the maximum circumferential pressure distortion in the AIP plane. One of these positions presents mean and peak distortion values lower than the other position. Furthermore, an alternating vortex pattern between two swirl patterns in the AIP plane is also identified. Finally, the relationship between pressure and swirl unsteadiness was investigated, and a link between the swirl distortion pattern and pressure distortion was identified. The identification of this relationship will allow geometrical changes in the air intake, leading to a reduction of the average circumferential distortion level, as well as a reduction of the maximum peak level achievable during a flight phase.

Multi-Stage Swirling Fluidized Bed: Part 1 - Numerical Analysis Procedure

Swirling Fluidized Bed (SFB) is a system that possess a plenum chamber and distributor air gap which leading up to dispersion of the airflow to the bed. The current SFB is in contrast with conventional fluidization systems whereby the effect of multi-stage through blades inclination angle (15°) and number of blades (60) was carried out. The simulation was used to compute and assess the performance outcomes of velocity distribution in a SFB. Therefore, the present study focuses on the numerical analysis procedure on the air flow distribution impacted by annular blade distributor arrangement in a Multi-stage SFB via ANSYS Fluent before a detailed study on selected variable would be carried out. As a consequence, the findings of the primary study that have been conducted are in line with expectations formed by earlier research.

Visualization experiment and flow homogenization optimization of the multi-path plenum chamber system using a perforated plate

Plenum chambers are commonly used to provide flow homogenization in ventilation and air conditioning systems. To reduce energy consumption and improve ventilation performance, the interior flow characteristics of a multi-path plenum chamber system were investigated through visualization experiments of flow field. As the flow distribution remained uneven after the primary structural parameters of the traditional chamber were optimized, a flow homogenization chamber was proposed by inserting a perforated plate to further improve flow uniformity. Taking the “one-inlet and two-outlet” chamber configuration as a case study, the proposed flow homogenization mechanism was analyzed in terms of flow control. The effects of the perforated plate geometry on flow uniformity and resistance performance were studied using two typical chambers with cross-sectional aspect ratio (W/H) of 1/1 and 5/1. The recommended dimensionless installation location of the perforated plate (y/L) in each chamber was determined to be 0.1 and 0.3 of the chamber length from the input, respectively, with an optimal aperture diameter (d) of 30 mm. In addition, the effectiveness of the flow homogenization chamber was verified using four commonly used air duct sizes, and different application scenarios were discussed for multi-path duct connections. The results show that the adjustment of perforated plate on flow field improved the flow distribution uniformity for chamber system with W/H = 1/1 and 5/1 by up to 87.50% and 56.71%, respectively, compared with the standard 90° T-junction connection.

Experimental and numerical study on cooling performance of a novel earth-to-air heat exchanger system with an inlet plenum chamber

Previous studies have focused on the horizontal buried pipe section regarding the performance improvement of the earth-to-air heat exchanger, showing limited attention paid to the vertical air inlet section. In this study, we proposed a novel earth-to-air heat exchange system utilising an inlet plenum chamber (IPC-EAHE) to pre-treat the outdoor air in the inlet section. To evaluate its cooling performance, a numerical model was developed and validated based on a field experiment. The results showed a good agreement between simulated and experimental data, with a maximum absolute relative error of 4.43 % for the outlet air temperature. Then comparative studies between the IPC-EAHE and traditional EAHE are conducted under three airflow rates. Results indicated that the IPC-EAHE has a lower and more stable outlet air temperature than traditional EAHE. Compared to the traditional EAHE, the IPC-EAHE reduces the fluctuation of outlet air temperature by 53.13 %, 29.84 %, and 26.60 % under the airflow rates of 190 m3/h, 380 m3/h, and 570 m3/h, respectively. This improves the free cooling potential of EAHE for buildings. Moreover, the IPC-EAHE can reduce the buried pipe length by around 60.30 %, 53.0 %, and 50.0 % for three airflow rates, respectively. The friction resistance loss of the IPC section is at least 20 % less than that of the traditional EAHE vertical inlet section. The above results demonstrate that the IPC-EAHE offers greater renewable energy utilization efficiency and less buried pipe length than the traditional EAHE.

EFFECT OF JET TO PLATE SPACING ON FILM COOLING PERFORMANCE IN A COMBINED IMPINGEMENT AND FILM COOLING ARRANGEMENT

The influence of jet to plate spacing on conjugate heat transfer from a flat plate with combined impingement and film cooling has been studied both numerically and experimentally. The flow configuration consists of a matrix of impingement holes and multiple staggered rows of cylindrical film holes. One side of the plate is impinged with air jets, while the other side is exposed to hot mainstream as well as the vented air from the film cooling holes. The effect of increasing jet to plate ratio (H/D = 0.4, 1.2, and 2.0) on film cooling flow structure and heat transfer is analyzed under conjugate boundary conditions. The flow and temperature patterns are predicted in the entire computational domain; namely, the plenum chamber, film holes, and mainstream-coolant interaction zone. The mainstream Reynolds number is varied from 49,050 to 130,800 while keeping the jet Reynolds number constant at 825 and the blowing ratio ranging from 0.6 to 1.6. The velocity, turbulence, and temperature distributions at the exit of the film hole together define the film coverage on the interaction surface. The thermochromic liquid crystal (TLC) technique is used to evaluate the surface temperature of the plate and validate the computed values of the surface effectiveness. Both measured and computed effectiveness distributions are found to be comparable. Increase in the H/D values beyond a certain limit causes decrease in film effectiveness on the interaction surface, especially downstream of the film hole. The influence of H/D is noticed for all the three blowing ratios investigated, albeit to varying degree.