Inlet Performance Research Articles

Numerical investigation on the effects of building configuration on discharge coefficient for a cross-ventilated dairy building model

To estimate the ventilation rate of buildings, the orifice equation with a fixed discharge coefficient (Cd) is often applied. However, values of Cd may be not a constant for the openings of naturally-ventilated dairy buildings. The main objective of this study was to investigate the influence of the building configurations on the Cd value. In addition, since the value of the pressure difference across the opening is crucial to the application of the orifice equation, another objective was to evaluate the accuracy of using the orifice plate method in pressure difference measurements. The investigations were carried out using computational fluid dynamics simulations. The results showed that applying the orifice plate method to measure the pressure drop could result in up to 18.9% relative error in estimates of Cd for the case with an opening ratio of 81.4%. Additionally, the value of Cd was found to be dependent on the opening ratio, the inlet opening position, and the inlet-to-outlet area ratio, but it was independent of the outlet opening position and the roof slope. It can be concluded that the Cd value should be specified according to the opening configurations in the application of the orifice equation.

Morphology, bedforms and bottom sediments of Mar do Ararapira, southern Brazil

Mar do Ararapira is an unusual estuary located at the border of Parana and Sao Paulo states, in a relevant area of ecological interest and where an opening of a new inlet occurred in August 2018. Differing from classical estuarine models Mar do Ararapira has three inlets, one with open sea and two with the estuarine systems of Baia de Trapande and Baia dos Pinheiros, the latter through an artificial channel named Canal do Varadouro. Mar do Ararapira also has multiple riverine inputs and the estuary head is not well defined. This paper presents: (a) Mar do Ararapira watershed characteristics, (b) an update of coastline shift close to the inlet and (c) a characterization of the estuarine bathymetry, bottom sediments and bedforms in 2009 and 2011. Comparison of parameters before and after an opening of a new inlet will help both the management of the estuary`s natural resources and the lives of the people inhabiting the surroundings. It is concluded that Mar do Ararapira corresponds to the lower part of an estuary. Its watershed extends 221.6 km 2 and is composed by three different morphologic sectors, which drains mountains and coastal plains. It presents a significant fresh-water input, estimated to range from 6.6 to 9.1 m 3 /s, and weak connectivity with its neighbor estuarine complexes. It is a shallow water body, with a mean depth of 4 m, where a deep main channel suggests intense bottom erosion by tidal currents. The ocean inlet migrates southwestward, mainly under the influence of high energy events. Prevailing bottom sediments are sand and muddy-sand. Subaqueous-sand-dunes and plane-beds are the most common bedforms at Mar do Ararapira. Three estuarine dynamically different sectors were recognized: (a) an inner sector with low tidal-current velocities and finer sediments; (b) a middle sector similar to a fluvial meander in dynamics, with higher tidal-current velocities and sandy sediments, where concave coasts are continuously eroded and convex coasts are silted; and (c) an outer sector, in which tidal-currents are segregated.

Path dependence characteristic of shock train in a 2D hypersonic inlet with variable background waves

The inlet equipped with a translating cowl is confirmed to have the ability of extending the range of flight Mach numbers. Along with the translation of cowl, the performance of inlet and background waves in the isolator vary continuously. Up to now, the behavior of shock train in opposite directions of translating cowl is still unknown. Numerical investigations have been conducted to study the path dependence characteristic of shock train with the application of dynamic mesh method. Based on the paths of shock train leading edges, it is discovered that the behavior of shock train is highly related to the variable background waves. Furthermore, the results reveal that the path dependence characteristic apparently embodies in the abrupt motions, average velocities of shock train, structures of shock train and oscillations. It is the discrepancies of critical internal contraction ratios, which the abrupt motions occur at, that lead to the hysteresis loops in the paths of shock train leading edges. In each hysteresis loop, the structures and average velocities of shock train in opposite directions of translating cowl are different. Meanwhile, the shock train would oscillate around the separation bubble, which intensifies the unsteadiness of shock train behavior. With the cowl moving upstream, the peak frequency of oscillation and the range of internal contraction ratio that oscillation takes place in are larger than the results obtained in the reverse direction.

Effectiveness of Stack Ventilation in a Two-Storey House in Hot and Humid Climate

The objectives of this research were to design stack ventilation and to study its effectiveness in a two-storey house in hot and humid climate of Bangkok, Thailand. Envelope openings at the rooftop and the entry door of the house were added to create height difference between inlet and outlet openings. Heat in the attic was utilized to make temperature difference in order to generate buoyancy for stack ventilation. The method of the study was experimentation in two existing houses, which had the same physical and had the most similar environment. The first house without stack ventilation was a base case. The second one was designed to integrate stack ventilation. Scientific instruments were installed in both houses at various positions. Air temperature, relative humidity and wind speed data were collected minutely for a few consecutive days for the evaluation of the experiment. It was founded that the house with stack ventilation had inside air temperature and relative humidity lower than those of the base case. The inside air temperature of the house with stack ventilation could be 0.7 Celsius lower than that of the base case. The relative humidity of the house with stack ventilation could have relative humidity of 12 % lower than that of the base case. Furthermore, the stack ventilation could make 1.06 air changes per hour with only 0.10% effective opening of building area having stack ventilation.

Design of Inward-Turning External Compression Supersonic Inlet for Supersonic Transport Aircraft

Inward-turning external compression intake is one of the hybrid intakes that employs both external and internal compression intakes principle. This intake is commonly developed for hypersonic flight due to its efficiency and utilizing fewer shockwaves that generate heat. Since this intake employ less shockwaves, this design can be applied for low supersonic (Mach 1.4 - 2.5) intakes to reduce noise generated from the shockwaves while maintaining the efficiency. Other than developing the design method, a tool is written in MATLAB language to generate the intake shape automatically based on the desired design requirement. To investigate the intake design tool code and the performance of the generated intake shape, some CFD simulation were performed. The intake design tool code can be validated by comparing the shockwave location and the air properties in every intake's stations. The performance parameters that being observed are the intake efficiency, flow distortion level at the engine face, and the noise level generated by the shockwaves. The design tool written in MATLAB is working as intended. Two dimensional axisymmetric CFD simulations validation has been done and the design meets the minimum requirement. As for the 3D inlet geometry, with a little modification on diffuser and equipping vent to release the buildup pressure, the inlet has been successfully met the military standard on inlet performance (MIL-E-5007D). This design method also has feature to fit every possible throat cross sectional shapes and has been proven to work as designed.Keywords— Inward-turning, Supersonic, Engine Intakes, Low- noise, Design Method

Determination of distribution factors for heavy n-alkanes (nC12-nC98) in high temperature gas chromatography

The ultimate purpose of this research work is to get an insight into the incomplete elution of heavy n-alkanes which along with thermal cracking, is one of the two main factors questioning the reliability of High Temperature Gas Chromatography (HTGC) analysis of heavy oils. For this purpose, knowledge of how the Distribution Factors vary with temperature is an essential requirement in the GC modelling.This study provides an extension of the data set of distribution factors for n-alkanes up to nC98H198 in a HT5 GC column over the temperature range 10 °C–430 °C, and introduces a method to determine the distribution coefficient of heavy n-alkanes by using two complimentary HTGC modes: i.) High-Efficiency mode, for efficient resolution with a long column operated at low flow rate with n-alkanes elution rate up to nC64, and ii.) true SimDist mode, with a short column operated at high flow rate for inefficient resolution with n-alkanes elution rate up to nC100.Furthermore, this study demonstrates the use of the in-house obtained distribution factors as the main input in the in-house GC model for the prediction of the retention times. Its validation has been carried out using distribution factors obtained at both constant flow rate and constant inlet pressure operating conditions, with an average relative error in the GC modelling at the same operating conditions of 4.4% for the former and 1.5% for the latter.This new extension of the data set of heavy n-alkanes distribution factors provides the basis for studying the partitioning and incomplete elution of heavy n-alkanes in HTGC analysis. Also, these new distribution factors can be used as input in GC modelling, to determine the optimum analytical conditions to improve the separation process and thus the HTGC practices.

Active control method for restart performances of hypersonic inlets based on energy addition

The restart performance of the inlet is crucial to a hypersonic air-breathing propulsion vehicle. An active flow control method based on energy addition for the restart of hypersonic inlets is brought forward in this paper. Using Reynolds Averaged Navier–Stokes equations method, the effects of energy addition parameters on the restart performances of hypersonic inlets are investigated and the restart process is presented. This study verifies that the present method is feasible to improve the restarting capability of hypersonic inlets. The restart performances rely heavily on the energy addition parameters. Using energy addition properly, it usually yields a better inlet performance and more importantly enables the inlet restart again; otherwise, the large separation bubble still exists. Investigations on energy addition parameters further reveal that energy addition always increases the mass flow rate, and its center far from the cowl facilitates restarting the inlet and decreasing the stagnation pressure losses. It also appears advantageous to work with energy addition at a moderate power consumption and effective radius. Besides, the restart process indicates that the parabolic shock induced by heated region plays an important role on the restart performance. It alters the separation bubble, broadens the flow passage and enables more deflected air into the inlet. The adverse pressure gradients in the entrance are greatly changed as well. Finally, results also suggest that an appropriate effective time for energy addition is sufficient to restart the inlet. The variations of hysteresis loops show that energy addition prompts the separated bubble to disappear and the inlet to restart in advance. As a result, the restarting Mach number declines and the operation range of hypersonic inlets prominently enlarges.

Parametric Design Study on Aerodynamic Characteristics of Variable Pitot Inlets for Transonic and Supersonic Civil Aviation

This paper reveals the influence of selected geometric parameters on the aerodynamic performance of circular variable aero engine inlets in transonic and supersonic civil aviation. The trade-off in inlet design and aerodynamic evaluation parameters are presented. The approach to investigate the dependencies between the aerodynamic and geometric parameters at different flight conditions by means of a parametric design study is introduced. The dependencies of inlet drag and efficiency from geometric parameters at flight speeds of Mach 0.95 up to Mach 1.6 are identified. Although entailing additional weight, the inlet length represents the parameter with the highest potential for drag reduction by up to 50% in the selected design space. Ideal geometries for variable pitot inlets are determined. After considering weight, their potential range benefit nearly disappears for subsonic applications, but remains above 20% for supersonic flight at Mach 1.6.

Effect of Cross-Ventilation and Solar Irradiation on IAQ as a function of Roof Angle

Natural ventilation is the most conventional and one of the significant alternative applications for energy efficiency. Cross-ventilation is commonly used in hospitals, shopping centres or greenhouses. In this study, cross-ventilation for a greenhouse was investigated. The greenhouse buildings may differ in design depending on the region and climate. Therefore, when natural ventilation methodology is carried out in these buildings, the effect of solar radiation should also be taken into consideration. There have been many studies on natural ventilation in the literature, but while these studies have been conducted, the impact of solar irradiation has never been combined. In the present study computational geometry was created according to 4 different roof inclinations: 0°, 15°, 30°, and 45° - provided that the inlet and outlet opening positions are fixed. Moreover, each inclination was simulated at the following hours of the day: 10:00, 13:00 and 16:00 in June. The hex-dominant grid was created for a computational domain using Cut-cell method and Renormalization-group (RNG) k-ε turbulence model provides the best results and efficient computational cost. In addition to this, Discrete Ordinates (DO) radiation model with SIMPLE algorithm was implemented for solar radiation effect. In order to decrease the temperature of the reference line, the evaporating cooling methodology was performed and a new PVC cover material was applied. Numerical predictions show that solar irradiance combined with roof inclination and outlet opening position has a significant effect on velocity and temperature distribution inside the building space. The air mass flow rate which aspirates from outlet increases considerably when the inclination angle is increased, also flow character changes according to configurations. Evaporative cooling creates a decrease in temperatures on the reference line up to 2 – 2.5°C when compared with the reference model.

Local analysis of airflow distribution in open concept passive houses

This paper presents the analysis of local air currents distribution near the inlet and outlet openings in a living room of study a pre-certified passive house located in Cluj-Napoca by CFD numerical simulation. The simulation domain is represented by an open space concept, comprising the living room and the kitchen, situated at the ground floor of the building. The used heat recovery ventilation system controls both the supply of fresh air through the inlet grilles, located on the floor of the living room and the extraction of exhaust air through outlet grilles with circular cross section positioned on the other side, in the kitchen’s ceiling. An area of interest has been selected to define the simulation domain. Numerical modeling has been carried out by means of a commercial software based on the finite element method to simulate a series of interconnected phenomena encountered in the analysed application. The dry air was chosen as working agent for the field of simulation/calculation. Its thermo-physical properties were selected from the program database. No slip limit conditions have been imposed for all the delimiting surfaces of the computational field. Inlet and outlet grilles were considered open borders for circulated air volume flow in three distinct analysed cases. For the simulation of the flow of the working fluid through the computational domain, the following simplifying assumptions were considered: stationary regime, incompressible fluid, constant temperature, isothermal jet, adiabatic system, without internal heat sources, without taking into account the mass forces. The discretization of the simulation domain was divided into an optimal number of finite variable elements, with a greater density near the border areas. The results of air currents distribution in the vicinity of grid areas, for inlet fresh air and outlet exhaust air, was done by analyzing the current lines, the velocity vectors and the velocity contours.

Use of Air Infiltration in Swine Housing Ventilation System Design

Abstract.The objective of this research was to develop and analyze the procedure for using recent air infiltration (AI) data collected from commercial swine finishing rooms (SFRs) in the design of negative pressure mechanical ventilation systems (VSs). Air infiltration is an integral part of any ventilation process. Infiltration reduces the pressure differential across planned inlets and at very low pressure differences, cold air jets may drop directly on the animals causing significant discomfort. In this article, a design procedure is proposed for swine housing ventilation systems with the influence of air infiltration included. The method was used on one SFR for which air infiltration data was collected by in-field testing. The air-jet throw, jet momentum number, a newly developed coverage factor, and Archimedes number were used to assess the influence of infiltration on predicted air-jet and fresh-air distribution and to help guide the design of planned inlets in SFR VSs with known infiltration. The analysis completed quantifies the severity of AI on air-jet and air distribution performance, and suggests that for the analysis room to ventilate properly requires a 50% reduction in AI levels beyond field measured curtain and fan infiltration. The analysis completed suggests a method for systematically planning three-dimensional ceiling inlet placement and operation and provides design guidance for new ceiling inlets suitable for SFR VSs. Keywords: Air distribution, Air-jets, Archimedes number, Infiltration, Jet Momentum Number.

Influence of Inlet Opening Size on the Operation of Natural Ventilation System of a Multistory Residential Building

Influence of Inlet Opening Size on the Operation of Natural Ventilation System of a Multistory Residential Building

A review of prewhirl regulation by inlet guide vanes for compressor and pump

To achieve the energy conservation and sustainable development, the prewhirl regulation by inlet guide vanes is proposed and rapidly developed for the compressor and pump. The inlet guide vanes change the flow pattern at the impeller inlet especially the velocity circulation, and then influence the performance of compressor and pump. This paper presents and discusses researches on the prewhirl regulation by inlet guide vanes. Researches include mechanism analysis of prewhirl regulation, experimental and numerical studies on the flow field, performance of compressor and pump with inlet guide vanes, influence of geometric parameters on performance of inlet guide vanes, and failure mode analysis and corresponding flow control methods.

Transparent Elemental Facade with an Integrated Ventilation Unit for a High-Rise Building – Development and Experimental Verification

Abstract The article documents the development of a modular transparent elemental facade. The cooperative development was realized in two areas, i.e., the development of facade ventilation units for an under-pressure ventilation system and experimental verification in a laboratory of a facade panel and optimization of its acoustic parameters. The task of controlled ventilation in modern residential buildings is to ensure the optimum quality of the interior environment and fulfill hygienic and thermal technical requirements that guarantee the comfort of the users. The paper discusses the development and experimental verification of atypical vertical ventilation units of an under-pressure controlled ventilation system for a residential high-rise building. A recommended concept for the facade´s details has been developed in relation to the ventilation system. Conceptual designs of alternatives to the air inlet openings of an under-pressure controlled ventilation system for the apartments with an atypical vertical geometry were proposed. An optimized alternative to air inlet openings in the bottom level of a vertical pilaster with the function of an air distribution channel for a ventilation system has been selected and developed. Laboratory experiments have verified the physical properties of the optimized alternative ventilation units of the under-pressure controlled ventilation system in their development cycle. The hydrodynamic regime of the air inlet openings of the controlled ventilation system has been verified by experimental research in a laboratory large rain chamber. The aerodynamic regime of a naturally controlled ventilation system was verified by experimental research in a large laboratory pressure chamber. The acoustic properties of the naturally controlled ventilation system were verified by experimental research in a laboratory´s acoustic chambers. The verified parameters of the ventilation units of the under-pressure controlled ventilation obtained by the experiment were compared with the design parameters. An experimental assessment of the mechanical, thermal and acoustical parameters of the elemental modular facade was carried out in a laboratory. At the end of the article, the results and conclusions of the laboratory experiment are summarized.

Effect of Side Gust on Performance of External Compression Supersonic Inlet

This Paper reports a computational investigation on the effects of side gust on the performance of a double-cone external compression supersonic inlet at Mach 1.8. The supersonic inlet geometry comprises three zones: a supersonic zone, a transit zone, and a subsonic zone. The supersonic zone is designed numerically using the Taylor–Maccoll method, while the transit and subsonic zones are designed using a methodology from literature. A three-dimensional structured mesh is generated by using the ICEM computational fluid dynamics software. Detailed three-dimensional simulations are performed using the ANSYS Fluent 18.2 code. The grid independency tests are performed by using local grid refinements and varying the number of grid points from 2.5 to 9.5 million. Further, the Fluent code is validated by comparing predictions with those using the SUPIN and Wind-US codes. The effects of side gust on the flowfield and oblique and normal shocks are analyzed by examining the Mach number and pressure distributions in the three zones. The inlet performance is characterized in terms of total pressure loss, flow distortion, and mass flow ratio parameters for a side gust of and gust angles of 30, 60, and 90 deg. Results indicate that the inlet performance is significantly affected by the side gust, especially at small gust angles.

Buzz evolution process investigation of a two-ramp inlet with translating cowl

In order to satisfy the requirement of high integration, the inlet equipped with translating cowl, which is able to adjust the geometries of combustor and inlet simultaneously, is proposed and studied. Numerical investigations are conducted to obtain hysteresis loop, stability boundary and buzz evolution process with various internal contraction ratios in wide range of flight Mach numbers. The dynamic mesh method is utilized to simulate the geometric adjustment. The results reveal that the buzz evolution process has obvious hysteretic characteristics under the change of translating direction. Meanwhile, the mechanism of inlet buzz mode transition is provided. Then, the effects that the translating velocities have on the oscillatory frequency, position of separation leading edge and dynamic drag are given. The higher velocity is able to restrain the intension of separation oscillation and enlarge the stable region, but has insignificant effect on the reduction of oscillatory frequency and dynamic drag. For specific velocities, there is no oscillation. Therefore, the appropriate velocity can be selected for the improvement of inlet stability. This research gives a full insight into the dynamic performance of a hypersonic variable-geometry inlet.

Effects of the aerothermoelastic deformation on the performance of the three-dimensional hypersonic inlet

The hypersonic inlet is more prone to deform when simultaneously subjected to aerodynamic load and harsh aerothermodynamic load. Moreover, the flow field of the hypersonic inlet is sensitive to configuration. Therefore, it is necessary to investigate the effects of the aerothermoelastic deformation on the flow structure and the performance of the hypersonic inlet. This study develops a loose coupling static aerothermoelastic analysis framework based on the CFD/CSD coupling method, and the one-way and the two-way aerothermal-aeroelastic coupling are both used in the analysis. Furthermore, the effects of the aerothermoelastic deformation on the flow structure and the performance of a three-dimensional hypersonic inlet are studied in detail. The reliabilities of the CFD method and the CFD/CSD coupling method are verified by the validation cases of DLR hypersonic inlet experimental model and the HIRENASD experimental model. The results obtained by the coupling methods are similar. However, the aerothermoelastic deformation obtained through the two-way coupling method is relatively larger, and the effects of the deformation on the inlet performance are more obvious. The maximum of the aerothermoelastic deformation exists at the leading edge of the inlet lip. The deformation changes the shock wave structure near the lip, strengthens the shock wave intensity inside the inlet, increases the length of the separated region and the temperature of the external wall, and changes the flow field of the exit. The aerothermoelastic deformation will lead to the increasing of the mass flow coefficient and the pressure rise ratio; however, it will decrease the total pressure recovery coefficient.

Vibration characteristics of the two‐stage throttle valve induced by cavitation

The effect of cavitation on vibration characteristics of a two-stage throttle valve is experimentally studied by changing inlet pressure, outlet pressure and opening. The shadow photograph of the flow field in the throttle is obtained by a high-speed camera, and the signal of vibration induced by cavitation of the two-stage throttle is obtained by an acceleration sensor. It can be concluded that the fixed cavitation and the travelling cavitation in the two-stage throttle valve occur at the back of the throttle orifice. The effect of cavitation on vibration intensity and power spectral density is obvious. There are two frequency peaks in the spectrum, which are located in the vicinity of 7.5 and 12.5 kHz, respectively. These peaks correspond to travelling cavitation and fixed cavitation. The cavitation vibration intensity increases with the increase in the cavitation intensity, and the centre frequency of the signal peak near 7.5 kHZ is also moving towards the low frequency.

Numerical prediction of thermal and airflow conditions of a naturally ventilated atrium and validation of CFD models

Natural ventilation as a major passive cooling strategy is growing in popularity, and atria, as a feature of buoyancy-driven natural ventilation, have been used with greater frequency in large modern buildings to enhance the flow regime of buildings. To have a reliable and suitable design, building simulation tools have become increasingly important in assisting designers to predict the temperature and airflow behaviours throughout atria. However, proper validation is required to ensure the accuracy of the prediction. Among the studies undertaken on atria, only a limited number have relied on full-scale experiments for validation. This study applied a full-scale four-storey atrium with solar assisted natural ventilation to validate four different turbulence models—“Realizable” k-ε, Standard k-ε, RNG k-ε, and SST k-ω—coupled with the Surface to Surface radiation model. The numerical predictions of all the computational fluid dynamic models were found to have good agreement with the experimental results for the temperature distribution and the air velocity rate. However, among the four tested models, RNG k-ε had the greatest similarity to the predicted temperature results. The results also show that direct ventilation in the atrium improves the airflow conditions of the attached space at the ground floor level with the inlet opening, even more than the atrium itself.

The dynamic response of a pressurized, hot, flexible fluid-conveying marine pipeline

ABSTRACT The transverse vibration of a pressurized, hot, flexible fluid-conveying pipe is investigated analytically via a coupled nonlinear partial differential equation where the effects of operating variables such as internal fluid temperature variation, mass ratio, pipe thickness, internal pressurization, Coriolis effect, axial acceleration of the internal fluid and cross-sectional area change, are fully captured. For this problem, a segment of a marine pipeline resting on the ocean floor is idealized as an elastic beam on an elastic foundation using the recently refined Euler-Bernoulli beam theory. Employing the hybrid Fourier-Laplace transforms, closed-form analytical expressions for the transverse natural frequencies are obtained in dimensionless form. In particular, two natural frequencies are noted to be associated with the phenomena as correctly identified in earlier results. Flow velocity was dependent on flow conditions and was found to increase with a decrease in the inlet operating temperature and thermal gradient. The operating pressure did not show any significant influence while the area deformation and pipe thickness increased. For the pipe thickness, the natural frequency was found to be similar irrespective of the thickness at the onset of the flow and decreased at a slower rate as it increased.