High Nozzle Pressure Research Articles

Numerical study on altitude-compensating mechanism of a permeable nozzle

A conceptual adaptive altitude compensation nozzle with a permeable wall (permeable nozzle for short) is proposed in the present study. The typical operating states of the nozzle are demonstrated using numerical methods and the underlying mechanism of its altitude compensation is interpreted. The numerical results show that, at low nozzle pressure ratios, the external atmosphere enters the nozzle through its permeable wall section, which inhibits the backflow at the nozzle wall, weakens the strength of the separated oblique shock, thus improves the low-altitude thrust performance of the nozzle. However, at high nozzle pressure ratios, the exhaust gas leaves the nozzle through its permeable wall, which weakens the expansion of the exhaust gas and reduces the thrust performance. The permeable nozzle is considered to possess altitude compensation ability when the enhancement in its low-altitude thrust performance surpasses the deterioration in high-altitude thrust performance. The thrust composition analysis of the permeable nozzle reveals that its altitude compensation ability derives from the internal pressure rise due to the atmospheric air penetration into the nozzle at low nozzle pressure ratios.

Equivalent notional nozzle model for high nozzle pressure ratio leakage of petrochemical high-pressure facility

Little work has been performed in the petrochemical safety field involving supersonic flows during accidental leakage in petroleum processing. The key technical challenge is on the changing process of gas cloud expansion after the jet. To address this, an equivalent notional nozzle model was developed for high single phase NPR (NPR＞2) gas leakage scenarios in petrochemical high-pressure facilities. This model aimed to determine the essential physical parameters of the equivalent cloud formed after air is drawn in with high NPRs. By utilizing CO2 as the gas phase, the validity of the equivalent notional nozzle model was assessed based on three crucial shock structure properties and the axial and radial velocity fields, the chocked flow intensity was applied as an indicator for the consistent trend of the jet velocity and decompression process of the high NPR gas leakage. The research findings unequivocally demonstrate the efficacy of the equivalent notional nozzle model in facilitating rapid numerical calculations for assessing the impact of high-pressure jets in the petrochemical industry.

Outflow of Supersonic Gas Jets from Axisymmetric Nozzle into a Space with a High Nozzle Pressure Ratios

Outflow of Supersonic Gas Jets from Axisymmetric Nozzle into a Space with a High Nozzle Pressure Ratios

Numerical study of spray cooling with flash evaporation

This work aims to apply Computational Fluid Dynamic (CFD) method to establish a flash evaporation spray cooling (FESC) model to simulate the heating process and find the optimum cooling performance. The heat transfer process during FESC is studied through numerical simulation using commercial code ANSYS FLUENT. The species transport model and the discrete phase model are applied to simulate the multiphase flow and heat transfer process. The turbulence effect is included. The effects of flow rate, nozzle pressure, nozzle angle, and the nozzle orifice size on spray cooling are investigated through analyzing the final surface temperature distributions. This work revealed the mechanism of the heat transfer process in FESC by means of particle tracks and velocity magnitude distribution. The simulated results for the effect of flow rate were compared with other researchers’ previous published experimental results. The comparison shows same trend, which verified the model and the simulation result. The optimum cooling performance is found by analyzing various working conditions. The results show that high flow rate, high nozzle pressure, small nozzle angle and small nozzle orifice can improve the FESC characteristics. The detailed mechanisms of these effects under various working conditions are also discussed. Under giving working conditions, the optimum cooling performance is obtained for the condition where mass flow rate of working fluid is 2L/min, the nozzle pressure is 100MPa, the nozzle angle is 15 degrees and the orifice size of the nozzle is 1mm.

Experimental and numerical investigation of transient starting of pre-evacuated exhaust diffuser in high altitude ground test

This paper deals with numerical and experimental investigation of exhaust diffuser transient starting in a high-altitude ground test of a thrust optimized parabolic (TOP) nozzle. The experimental investigation has focused on cold gas flow inside TOP nozzle and second throat exhaust diffuser (STED), performed to examine flow unsteadiness at the starting phase. In order to identify physical phenomena during STED starting, unsteady numerical simulations have also been carried out. Two major parameters including nozzle pressure slope and pre-evacuated regions along the diffuser have been examined. The results indicate elimination of the cap shock separation or restricted shock separation (RSS) pattern during the transient starting at high nozzle pressure slope with pre-evacuation. Also, considerable reduction in the starting time is achieved, so that it causes more desirable instantaneous starting of the diffuser in some conditions. However, at average and lower nozzle pressure slopes, RSS pattern still develops inside the nozzle. Investigation of the effect of pre-evacuation spaces along the diffuser on the course of evacuation development indicates that the larger the pre-evacuation space along the diffuser, the more desirable is the STED operation quality, whereby the starting time decreases considerably. It is shown that with a given nozzle pressure slop, enlarging the pre-evacuation area from the diffuser inlet to the middle of the second throat results in a 25% reduction in diffuser starting time, and the further increase of the pre-evacuation area to the end section of the diffuser leads to instantaneous starting of the diffuser. Furthermore, we found that initial pre-evacuation pressure value has less effect on the diffuser starting process, so that for a given nozzle pressure slop and a pre-evacuation area by reducing this parameter five times, the starting time is reduced by only 3.75%.

Experimental and feasibility study on nano blended waste plastic oil based diesel engine at various injection pressure: A value addition for disposed plastic food containers

Fuel obtained from waste plastic has been used in this study due to the lavish consumption, and non-stop price hiking made the researchers focus on finding a suitable substitute for conventional fuel. The plastics were non-biodegradable, and also its continuous usage in our daily life together created awareness about waste plastic management among us. With this, plastic oil could be a promising alternative fuel and also solves the issue of seating waste plastics in landfills. Even though plastic oil has a closer calorific value and viscosity to diesel, its volatility is less than diesel. In order to improve its volatility, a titanium dioxide oxide nanoparticle of 50 ppm, 100 ppm, and 150 ppm was doped. A single-cylinder diesel engine's performance, emission, and combustion phenomena were tested with nano blended waste plastic oil at three different fuel injection pressure of 210, 230 and 250 bar, respectively and the results were analyzed. An improvement in engine characteristics was recorded for nanoparticle blended fuels. High nozzle opening pressure improves the spray penetration inside the engine cylinder, promoting the combustion quality. The study concluded that blending 150 ppm Titanium-dioxide with waste plastic oil would be a suitable alternative for diesel engines operating at 230 bar of injection pressure.

Experimental investigation of high‐pressure hydrogen gas jet impingement characteristics of single‐hole cylindrical injector

AbstractHigh‐pressure hydrogen direct injection technology can enable an internal combustion engine to attain high thermal efficiency and discharge clean emissions; hence, the advantages provided by hydrogen jet impingement are crucial. This paper presents an experimental investigation of the high‐pressure hydrogen direct injection from a single‐hole cylindrical injector. A test rig with a spring set was designed based on the impulse conservation law to test important high‐pressure hydrogen jet impingement parameters, such as jet impingement force and impulse. The results show that the hydrogen gas jet exhibits a two‐zone behavior. In Zone I (near‐field dynamic region), the jet impulse is not conservative, and the jet characteristic parameters (jet impingement force and impulse) fluctuate—first decreasing and then increasing. In Zone II, the jet impulse is conservative. This two‐zone jet feature is induced by shockwaves because a high‐pressure hydrogen jet with a high nozzle pressure ratio reaches its sonic speed at the nozzle outlet. The Mach disk height is the inflection point of these two zones. Moreover, the hydrogen injection pressure has a considerable influence on the gas jet. As the injection pressure increases, the hydrogen jet impingement force and impulse increase. Both jet parameters have a linearly increasing relationship with injection pressure.

Investigation of suddenly expanded flows at subsonic Mach numbers using an artificial neural networks approach.

The purpose of this study is to explore two concepts: first, the use of artificial neural networks (ANN) to forecast the base pressure (β) and wall pressure (ω) originating from a suddenly expanded flow field at subsonic Mach numbers. Second, the implementation of Garson approach to determine the critical operating parameters affecting the suddenly expanded subsonic flow process in the subsonic range. In a MATLAB environment, a network model was constructed based on a multilayer perceptron with an input, hidden, and output layer. The network input parameters were the Mach number (M), nozzle pressure ratio (η), area ratio (α), length to diameter ratio (γ), micro jet control (ϵ), and duct location to length ratio (δ). The network output included two variables; base pressure (β) and wall pressure (ω). The ANN was trained and tested using the experimental data. The experimental results found that micro-jet controls were successful in increasing the base pressure for low Mach numbers and high nozzle pressure ratios. It was also found that the wall pressure was same for with and without micro jet control. The ANN predicted values agreed well with the experimental values, with average relative errors of less than 5.02% for base pressure and 6.71% for wall pressure. Additionally, with a relative significance of 32% and 43%, the nozzle pressure ratio and duct location to length ratio had the highest influence on the base pressure and wall pressure, respectively. The results demonstrate that the ANN model is capable of accurately predicting the pressure results, enabling theoretical foundation for research into pressure distribution in aerodynamic systems.

Effect of outlet temperature and total soluble solid in 2-stage spray dryer on black tea powder extract production

The black tea powder extract produced through the spray drying technique is an alternative to tea steeping or brewing in the industry. The production of black tea powder extract using the 2-stage spray dry method still has problems such as different colour, product swelling or inflate and blocking. To determine the source of the problem, this study used varied outlet temperatures 105°C, 110°C, 115°C, 120°C and total soluble solids (TSS) 31.3, 35.2, 37.2, 43.9, 44.1, 47.4. Spraying through 2-stage spray dryer with combi fluid bed and high nozzle pressure atomizer model SC 40 SDX III by Delavan. The results show a significant difference between the outlet chamber temperatures with the flowrates, the pressures, and the densities. An increase in outlet temperatures by a multiple of 10°C can significantly reduce the pressure and the flow rate, while the temperatures multiple of 20°C can significantly reduce the densities, but not for the moisture contents and the powder colours. Changes in the outlet temperatures did not have a 0.2% effect on the steeping colours but were affected by TSS. The higher TSS’s value gives an increase in flow rate, pressure, moisture content and steeped powder colours of 0.2%

Investigation of supersonic twin-jet coupling using spatial linear stability analysis

Abstract

Numerical investigation of second throat exhaust diffuser performance with thrust optimized parabolic nozzles

Free or restricted shock separation phenomena can occur inside a thrust optimized parabolic (TOP) nozzle during over-expanded operations. In the case of restricted shock separation, a cap shock pattern forms in the nozzle which leads to a substantial total pressure drop. This induces further related issues in the process of ground testing of such nozzles using a second throat exhaust diffuser (STED). In the present study, the flow physics in several TOP nozzles operating at over-expanded conditions is investigated numerically. At first, the strong effect of the initial expansion angle of a TOP nozzle on flow separation pattern and shock structure is demonstrated. Results reveal that for high initial expansion angles, restricted shock separation occurs even at low nozzle pressure ratios, while free shock separation takes place for small initial expansion angles at even high nozzle pressure ratios. Subsequently, the effect of separation patterns in TOP nozzles on the starting pressure of a STED is studied. Current results show that the presence of a restricted shock separation pattern leads to a considerable increment of the critical cross sectional area of the flow inside the diffuser. Therefore, the minimum starting pressure of the STED is increased up to 30% after the resizing of the second throat area to eliminate the flow choking inside it.

Effects of the Helmholtz Resonator on the Hartmann Whistle Operating at a High Nozzle Pressure Ratio

A numerical simulation is carried out to investigate the effect of the Helmholtz resonator capacity on the Hartmann whistle operating at high values of the nozzle pressure ratio using the turbulence model. The results of the present numerical simulations are compared to experimental data. The simulation results show that the frequency and amplitude of the Hartmann whistle with the Helmholtz resonator are obviously lower as compared to the conventional Hartmann whistle. Moreover, the Mach number contours and streamlines indicate that the Helmholtz resonator does not affect the shock-cell structure between the nozzle and the cavity, and the Hartmann whistle with the Helmholtz resonator has a. jet regurgitant mode that is different from the Hartmann whistle with a. straight resonator. The diameter of the Helmholtz resonator is an important factor affecting the fundamental frequency.

Numerical Investigation on a New Concept of Shock Vector Control Nozzle

Shock vector control (SVC) based on transverse jet injection is one of the fluidic thrust vectoring (FTV) technologies, and is considered as a promising candidate for the future exhaust system working at high nozzle pressure ratio (NPR). However, the low vector efficiency (η) of the SVC nozzle remains an important problem. In the paper, a new method, named as the improved SVC, was proposed to improve the vector efficiency (η) of a SVC nozzle, which enhances the vector control of primary supersonic flow by adopting a bypass injection. It needs less secondary flow from high pressure component of an aero-engine and has smaller influence on the working character of an aero-engine. The flow mechanism of the improved SVC nozzle was investigated by solving three-dimensional Reynolds-averaged Navier--Stokes with shear stress transport (SST) κ–ω turbulence model. The shock waves, jets-primary flow interactions, flow separation, and vector performance were analyzed. The influences of aerodynamic and geometric parameters, namely, NPR, secondary pressure ratio (SPR), and bypass injection position (Xj.ad.) on flow characteristics and vector performance were investigated. Based on the design of experiment (DOE), the response surface methodology (RSM) and the simulation model of an aero-engine, a method to estimate the coupling performance of the improved SVC nozzle and an aero-engine was studied, and a new balance relationship between the improved SVC nozzle and an aero-engine was established. Results shows that (1) with the assistance of bypass injection, the jet penetration and the capability of vector control are largely improved, resulting in a vector efficiency (η) of 1.98 deg/%-ω at the designed NPRD = 13.88; (2) in a wide range of operating conditions, larger vector angle (δp), higher thrust coefficient (Cfg), and higher vector efficiency (η) of the improved SVC nozzle were obtained, (3) in the coupling process of the improved SVC nozzle and an aero-engine, a δp of 18.1 deg was achieved at corrected secondary flow ratio of 10% and corrected bypass ratio of 6.98%, and the change of the thrust and the specific fuel consumption (SFC) were within 12%, which is better than the coupling performance of a SVC nozzle and an aero-engine.

Effects of the Helmholtz Resonator on the Hartmann Whistle Operating at a High Nozzle Pressure Ratio

Effects of the Helmholtz Resonator on the Hartmann Whistle Operating at a High Nozzle Pressure Ratio

A Numerical Study on Jet Structure and Noise Emission of Underexpanded Radial Jet

In this study, an underexpanded radial jet issuing from a small gap between two circular tubes facing each other is investigated numerically. Radial jet is formed, for example, downstream of high-pressure valves in piping system and of poppet valves in engines, and causes many industrial problems such as the noise generation and the fatigue failure of structure. In this study, the jet issuing from a small gap between two tubes with same diameter is numerically simulated. The flow field is assumed to be axisymmetric against the central axis of tubes and to be symmetric against the intermediate plane between the exits of two tubes. The axisymmetric Euler equations are solved using symmetric TVD (Total Variation Diminishing) scheme. The effects of nozzle pressure ratio and of diameter of circular tubes on the structure and the behavior of jets are examined. Typical cell structure of underexpanded jet appears in radial jet and the length of cell becomes smaller in downstream region because the jet spreads radially like a disc. The length and width of first cell are larger with higher nozzle pressure ratio. Many vortices are generated one after another near the jet boundary and move downstream, which cause the oscillation of jet. Outside of jet, two types of density waves are observed. One of them propagates toward the nozzle (toward the upstream region) and the other propagates in opposite direction. Focusing on the pressure change caused by the former waves, which is related to well-known screech, dominant frequency obtained by FFT analysis was found to become lower with higher pressure ratio and smaller diameter of tube.

Shock oscillation in highly underexpanded jets**Project supported by the National Natural Science Foundation of China (Grant No. 11602028) and the Science and Technology Project of General Administration of Quality Supervision Inspection and Quarantine of China (Grant Nos. 2017QK119 and 2017QK188).

The oscillatory motions of shocks in highly underexpanded jets with nozzle pressure ratios of 5.60, 7.47, 9.34, and 11.21 are quantitatively studied by using large eddy simulation. Two types of shock oscillations are observed: one is the Mach disk oscillation in the streamwise direction and the other is the shock oscillation in the radial direction. It is found that the Mach disk moves quickly in the middle of the oscillatory region but slowly at the top or bottom boundaries. The oscillation cycles of Mach disk are the same for different cases, and are all dominated by an axisymmetric mode of 5.298 kHz. For the oscillation in the radial direction, the shocks oscillate more toward the jet centerline but less in the jet shear layer, and the oscillation magnitude is an increasing function of screech amplitude. The cycles of the radial shock oscillation switch randomly between the two screech frequencies for the first two cases. However, the oscillation periodicity is more complex for the jets with high nozzle pressure ratios of 9.34 and 11.21 than for the jets with the low nozzle pressure ratios of 5.6 and 7.47. In addition, the shock oscillation characteristics are also captured by coarse mesh and Smagorinsky model, but the coarse mesh tends to predict a slower and weaker shock oscillation.

Mitigation of impinging tones using central protrusion

This article demonstrates that a simple modification such as installing a protrusion on an impingement plate can lead to reduction of jet impingement tones. This experimental work compares the acoustic variations in jets impinging on a flat plate, and plates with a central protrusion. The key strategy here is the modification of the stagnation flow region brought about by the introduction of the central protrusion. It is observed that the toneless acoustic power is almost the same for jet impinging on the plate with and without the central protrusion. It is also found that the protrusion is more effective in reducing tones in supersonic impinging jets than the tones in subsonic impinging jets. However, there is a slight increase in acoustic power when the jet impinges on a larger protrusion (greater than jet diameter) at high nozzle pressure ratios. Further, high speed flow visualization is carried out to relate the shock oscillations with the tonal frequencies. The noise source location is estimated by performing FFT on the flow visualization images. The acoustic and optical measurements are compared in terms of tonal frequency and found to be in agreement with each other.

Jet noise reduction using co-axial swirl flow with curved vanes

Experimental studies are carried out to reduce the jet noise using co-axial swirlers in the form of curved vanes fixed in an annular passage. The swirl numbers considered for the present work ranged from 0 to 1.31, and the corresponding swirl vane angles ranged from 0 to 60°. The nozzle pressure ratios studied ranged from 1.8 to 6. The acoustic far field study at subsonic conditions revealed the presence of transonic tones for the non-swirl jet. However, swirl eliminates the transonic tones and a weak swirl is most efficient for noise reduction at subsonic conditions. The centerline total pressure measurements indicate the reduced core length for the swirl jets compared to the non-swirl jets. At supersonic conditions, the non-swirl jet emits the highest noise at all the emission angles compared to the swirl jets. The swirl jets are free from screech tones, and have lower amounts of shock associated noise, even at high nozzle pressure ratios. The centerline total pressure measurements and schlieren visualization studies show that shock cell spacing and the number of shock cells are reduced in the swirl jets compared to the non-swirl jet.

Underexpanded Jet Development from a Rectangular Nozzle with Aft-Deck

An experimental study is reported of underexpanded supersonic jet plumes issuing from a high-aspect-ratio convergent rectangular nozzle. Schlieren visualization, Pitot probe, and Laser Doppler Anemometry measurements are carried out to capture the plume development in the near field, and in particular the effect on the plume flow of a finite-length extended shelf or aft-deck attached to the lower nozzle wall. This creates asymmetry in the inviscid shock cell pattern and the entrainment characteristics, both of which influence shear-layer growth and plume trajectory. A net pressure force is induced on the aft-deck wall, which leads to transverse deflection of the jet plume once it leaves the aft-deck, both upward and downward, depending on aft-deck length and nozzle pressure ratio. For sufficiently high nozzle pressure ratio and a sufficiently long aft-deck, separation and reattachment of the plume from the aft-deck is observed. Detailed mapping of both mean velocity and turbulence in the plume near field has been carried out, enabling comparison of flow behavior for a clean nozzle and a nozzle with aft-deck. The data provided are proposed as a suitable benchmark validation test case for computational fluid dynamics studies of rectangular nozzle plumes with aft-deck interaction effects.

Laser initiated reactions in N2O clusters studied by time-sliced ion velocity imaging technique

Laser initiated reactions in N2O clusters were studied by a time-sliced velocity imaging technique. The N2O clusters, (N2O)n, generated by supersonic expansion were irradiated by an ultraviolet laser around 204 nm to convert reactant pairs, O((1)D2)-(N2O)n-1. The NO molecules formed from these reactant pairs were ionized by the same laser pulse and their velocity distribution was determined by the time-sliced velocity imaging technique. At low nozzle pressure, lower than 1.5 atm, the speed distribution in the frame moving with the clusters consists of two components. These components were ascribed to the products appeared in the backward and forward directions in the center-of-mass frame, respectively. The former consists of the vibrational ground state and the latter consists of highly vibrational excited states. At higher nozzle pressure, a single broad speed distribution became dominant for the product NO. The pressure and laser power dependences suggested that this component is attributed to the product formed in the clusters larger than dimer, (N2O)n (n ≥ 3).