Passive flow control in liquid-propellant rocket engines with cavitating venturi

The cavitating venturi is using to provide constant mass flow rate of liquid which is passing through a passage, independent of downstream pressure changes. A cavitating venturi is a converging-diverging nozzle with a suitable throat area for passing flow. The flow rate is a function of the upstream pressure, the throat area, the density and saturated pressure of the liquid. An experimental setup with the capability of supplying constant water flow rate, upstream pressure and temperature was designed and manufactured. Three cavitating venturies were designed and built to investigate the effect of cavitating venturi size on its mass flow rate and capability of performance venturi in wide ranges of flow rates. Three different sets of experiments were conducted to ensure the performance of the venturi to keep constant mass flow rate independent of downstream pressure. In the experiments, under different downstream and upstream pressure conditions, the mass flow rates were examined. The results show that if the ratio of downstream pressure to upstream pressure is less than 0.8, the mass flow rate is constant and independent of the downstream pressure. Whenever pressure ratio exceeds from 0.8, the venturi acts like an orifice.

Cavitating venturis are common as flow control devices in liquid rocket engines. The fact that cavitating venturi provide a constant flow rate under varying downstream pressure, they are particularly useful during the ignition transient when the downstream pressure in the combustion chamber rises rapidly. Pressure recovery is one of the key design issues for cavitating venturis. By using empirical relations a cavitating venturi can be designed with acceptable pressure recovery at a desired mass flow rate. However dimensionless parameters such as critical cavitation number and discharge coefficients are geometry and fluid dependent which cannot be achieved by the empirical relations. These parameters can be deduced from computational fluid dynamics simulations. Therefore, the aim of this study is to model cryogenic cavitating flows by using a commercially available flow solver ANSYS Fluent and validating the simulations with the experiments.

Flow-blurring (FB) is a twin-fluid atomization technique that generates fine sprays through internal turbulent mixing. This study presents a parametric computational investigation of an FB injector operating with air and various liquids at ambient pressure. A validated unsteady two-phase solver based on the Volume of Fluid (VOF) method is used to model the injector at different air-to-liquid mass flow rate ratios (ALRs). Parameters such as penetration length, volume fraction, static pressure, vorticity magnitude, and turbulent kinetic energy are analyzed to understand flow dynamics. The results identify three distinct flow regimes: air-dominant, liquid-dominant, and bubbly flow. Screening analysis of a full factorial design of 32 cases shows that liquid mass flow rate and dynamic viscosity are the most influential factors in penetration length. The resulting penetration length varies between 2 [mm] and 8.5 [mm] across the design space. A correlation analysis confirms these findings and reveals important two-way interactions between parameters, such as the positive effect of combined liquid and air mass flow rates. This insight offers a promising pathway for optimizing flow-blurring injectors in various applications.

On the effect of filters for the design of solid propellant gas generators

<div class="section abstract"><div class="htmlview paragraph">This paper studies the “Experimental testing of spray characteristics of swirler injector without guide vanes in Liquid Propellant Rocket Engines”. The purpose of a fuel injector is to inject and control the flow of the propellants into the combustion chamber. It consists of Tangential ports, a swirls chamber, a converging spin chamber, and a discharge orifice. Kerosene as fuel and liquid oxygen as oxidizer were employed here. To pressurize the propellants, nitrogen gas is used and the pressurized pipeline is controlled with an open/close ball valve and measure the inlet pressure using a pressure gauge. When a propellant comes through the inlet has a tangential velocity and it causes the propellants to swirl inside the swirl chamber at the exit the propellant comes with rotational momentum and forms a liquid film and then the friction between the propellant and air accelerates and disrupts the liquid film and converts into very tiny droplets. The exit mass flow rate, spray cone angle, and spray cone length with different inlet pressures and inlet diameters are measured. A graph is plotted between inlet pressure, and spray cone angle, penetration length. The theoretical mass flow rate is calculated using Bernoulli’s equation, taking the coefficient of the discharge as one and plotted a graph with the given data and comparing it with the experimental data. The accurate atomization increases the combustion efficiency, burns the propellant completely without leaving any unburnt propellant in the combustion chamber, and minimizes combustion instability.</div></div>

A complete set of equations describing the conservation of mass, momentum, and energy, and multicomponent transport and chemical reaction in a liquid propellant rocket (LPR) engine are given, along with appropriate boundary conditions. The formulation includes a detailed description of the two-phase (gas/liquid) flow in terms of a moving boundary problem, with droplets and vapor occupying time-dependent subdomains of the LPR chamber. Several sensor and actuator types are considered in detail, and their mathematical descriptions are incorporated into the differential equations and boundary conditions.

The injection of supercritical fuel into a quiescent gas environment was experimentally studied to elucidate the effects of thermophysical and transport properties near the critical point on jet appearance, shock structures, and choking. Ethylene and nitrogen were used to simulate interactions between fuel and air. Conditions near the thermodynamic critical point of ethylene are considered, with supercritical temperatures and pressures upstream of the injector and subcritical pressures downstream of the injector. Flow visualization showed an opaque region resulting from fuel condensation when fuel was injected at near room temperature. At higher injectant temperatures, the ethylene jet was found to have a shock structure similar to that of an underexpanded ideal-gas jet. Mass flow rates were found to be insensitive to the variation of back pressure, indicating that the jet flow is choked. Mass flow rates were normalized by those values calculated for ideal-gas jets under the same conditions. The normalized mass flow rate first increases as injection conditions approach the critical temperature, apparently because of the rapid increase in fluid density, and then decreases, possibly as a result of the coexistence of liquid and gas phases at the nozzle exit.

Performance and image analysis of a cavitating process in a small type venturi

Thermal recycling analysis in regenerative cooling channels based on liquid rocket engine cycles

A vacuum pressure tracking system with high-speed on-off valves is a discontinuous system due to the discrete nature of high-speed on-off valves. Chamber pressure changes in the system are determined by the mass flow rates during the processes of charging and discharging. Here, a sliding mode controller with an asymmetric compensator based on average mass flow rate is designed for accurate vacuum pressure tracking. The controller output signal is converted into the duty cycles of the high-speed on-off valves via a pulse width modulation pulsing scheme. Owing to the extreme asymmetry of the processes, an asymmetric structure comprising one high-speed on-off valve in the charging unit and three high-speed on-off valves in the discharging unit is applied to weaken the impact of asymmetry. In addition, an asymmetric compensator is also designed to modify the pulse width modulation pulsing scheme to further eliminate the asymmetry. Experimental results indicate that the proposed controller achieves better performance in pressure tracking with the asymmetric compensator overcoming process asymmetry and enhancing system robustness.

Dynamic features of a cavitating venturi have been a topic of investigation for the past few decades. This review presents state-of-the-art of experimental and numerical studies in cavitating venturi to address the challenges in understanding flow behavior and developing reliable numerical models. Many experimental studies have shown that two strongly coupled mechanisms, namely, Re-entrant Jet and the bubbly shock influence the cavitation zone behavior. We provide pointers from the past and recent studies to the influence of geometry and operating conditions, introducing changes in cavity oscillation. From an operational viewpoint, the modeling studies need to predict four crucial parameters related to its steady and dynamic operation: choked mass flow rate, operating pressure ratio range, cavitation length, and frequency of cavity oscillations. In this paper, we discuss the possible ways to properly configure a one-dimensional (1D) model, which can be a handy tool for extracting the key integral parameters. Realistic predictions require direct numerical simulations, which is not always an economically viable option. Recent three-dimensional (3D) simulations with compressible formulations for flow field and a cavitation model coupled with large eddy simulations to handle turbulence have achieved some success in predictions. Many simplified approaches have been popular. In this paper, we systematically bring out the predictability limits of popularly used mixture models coupled with cavitation and turbulence in more commonly studied two-dimensional (2D) and fewer three-dimensional geometries. Two-fluid models could provide answers, but further studies are required to mitigate the modeling challenges and to enable realistic predictions of the steady and dynamic features of this elegant flow control device for a chosen application.

In this research, design methods of radial flow compressor volutes are reviewed; the main criteria in volute primary designs are recognized and the most effective ones are selected. The effective parameters, i.e., spiral cross-section area, circumferential area distribution, exit cone, and tongue area of the compressor volute are parametrically studied to identify the optimum values. A numerical model has been prepared and verified through experimental data which are obtained from the designed turbocharger test rig. Different volutes are modeled and numerically evaluated using the same impeller and vane-less diffuser. For each model, the volute total pressure ratio, static pressure recovery and total pressure loss coefficients and the radial force on the impeller are calculated for different mass flow rates at design point and off-design conditions. The volute which shows better performance and causes lower the net radial force on the impeller at desired mass flow rates is selected as an optimal one. The results show the volute design approach differences at the design point and off-design conditions. Improving the pressure ratio and reducing total pressure loss at design point may result in the worse conditions at off-design conditions as well as increasing radial force on the impeller.

This study numerically investigates the spray dynamics and time-lag effects in high-pressure liquid oxygen (LOX) impinging jet atomization under three scenarios: varying pressure differences without oscillations, upstream pressure oscillations with different amplitudes, and downstream pressure oscillations. By coupling the Volume of Fluid method with the Lagrangian Particle Tracking model, the atomization process—encompassing liquid sheet breakup, fragment formation, and droplet generation—is analyzed through high-fidelity simulations. The results show that, in the absence of pressure oscillations, increasing the pressure difference influences jet velocity and droplet mass flow rate but has minimal effect on the Sauter Mean Diameter (SMD) within the considered range. Even without oscillations, the droplet mass flow rate exhibits large, nonperiodic fluctuations, reflecting the intrinsic instability of the atomization process, which may contribute to combustion instability. When external pressure oscillations are applied, either at the injector inlet or combustion chamber outlet, periodic variations are induced in both mass flow rate and SMD of the generated droplets. The amplitude of oscillation is positively correlated with the intensity of pressure fluctuations. Additionally, time-lag phenomena are observed: there is a negligible time lag between pressure oscillations and LOX mass flow rate fluctuations, while significant delays are seen between LOX mass flow rate and droplet mass flow rate oscillations. The time lag between LOX mass flow rate and SMD oscillations is comparatively shorter. These findings provide insights into transient spray behavior and temporal correlations in high-pressure impinging jet atomization, aiding the optimization of injector designs and improving combustion stability in rocket engines.

Complete burning of liquid propellants droplets is very important to avoid combustion instability and to get higher specific impulse from liquid rocket engines. Combustion takes place in gaseous phase and reaction is fast. So, the time consumed by a droplet for complete burning is the time taken by a droplet to get evaporated. An analytical mono component fuel droplet evaporation model is developed and proposed for droplet evaporation in liquid rocket engine based on heat and mass transfer. Effect of the fuel droplet curvature on vapor pressure is incorporated in the model. The model is applied on a small-scale combustion chamber of bi-propellant liquid rocket engine where fuel concentration away from droplet is not zero. A code is generated and applied. The results of the model show that fuel droplet diameter, combustion chamber pressure, chamber diameter, mass flow rate and droplet relative velocity with hot gas has significant effects on the life of droplet and characteristic length. Effects of chamber pressure and diameter are more significant for larger droplet size.

This study describes the results on the performance of one vehicle air conditioning system. The coefficient of performance, evaporator cooling capacity, compressor power consumption, total mass flow rate, vapor mass flow rate, liquid mass flow rate and oil in circulation, pressures and temperatures of refrigerant at every component (inlets and outlets) are measured and analyzed with the variation of the outside temperatures at the evaporator and condenser, the speed of the compressor, refrigerant charge and oil charge. The systematical experimental results obtained from this real-size test system depict the relations between the above parameters in a vehicle air conditioning system, which constitute a useful source for vehicle air conditioning systems design and analysis. The vapor quality (two-phase flow) measurements realized in this work provide an extremely important tool for diagnosing the system performances.