Jet Interaction Flow Research Articles

Numerical simulation of jet interaction flow field of complex configuration based on hybrid grid method

Abstract The supersonic/hypersonic jet interaction flow field includes many fluid phenomena such as shock waves, separation and reattachment of the boundary layer, expansion wave, Mach disk, shear layer, and so on. The complexity of the jet interaction flow field makes it difficult to simulate accurately, and the structured grid method is generally used in engineering applications. However, the structured grid has many shortcomings when dealing with complex configurations, and the traditional hybrid grid method has the problem of insufficient accuracy. In the paper, a structured/unstructured grid algorithmic coupling numerical simulation method is developed. Firstly, the feasibility and accuracy of this method are verified by numerical simulation of the jet interference flow field of cone-cylinder-skirt shape, along with a comparison with the results of the experiment and structural method. Then, the jet interference flow fields of the rudders and the grid fins configuration are simulated to show the efficiency of the method, and the accuracy is further verified. The results show that the hybrid numerical simulation method can save grid generation time and grid quantity to a certain extent when compared with the structural, showing higher accuracy, which provides an accurate and efficient solution to jet interaction problems with complex configurations.

Mesh Adaptation for Simulating Lateral Jet Interaction Flow

Under the condition of supersonic incoming flow, a missile lateral jet flow field has complex flow structures, such as a strong shock wave, an unsteady vortex and flow separation. In order to improve ability to capture complex flow structures in numerical simulation of lateral jets, this paper proposes a combined-grid adaptive method. When combined with finite volume approximation of second-order and h-type adaptive technology, our method was verified by numerical experiments, which shows that wave structure and vortex structure in the jet flow field can be effectively captured at the same time. In comparison of uniformly refined mesh results, it was found that accuracy of computed results and resolution of characteristic flow structures were significantly improved after mesh adaptation. In comparison of the pressure coefficient, it was found that the error between the adaptive mesh and the uniformly refined mesh was smaller, and the maximum errors of the base grid, adaptive grid and uniformly refined grid were 92.1% and 12.3%.

Numerical Simulation of Jet Interaction Flow Field with Different Flow Rates

In this paper, the complex disturbance flow caused by the interaction of jets with different flow rates and hypersonic incoming flow on a cone-cylinder-skirt of revolution is numerically studied, the typical shock wave structure and the influence range caused by the jet interaction are given, and the effect of the jet flow rate on the interaction flow field is discussed. The results show that the interaction between the jet flow and the incoming flow increases with the rise of the jet flow rate, and the influence range of the wrapping effect enlarges. If the jet flow rate is equivalent to the incoming flow rate, the leading edge separation line forms a closed loop.

Numerical Investigation on Aerodynamic Characteristics of an Active Jets-Matrix Serving as Pitch Control Surface

To facilitate future Hypersonic Flight Vehicle (HFV) implementation with high maneuverability throughout its reentry trajectory, an Active Jets-Matrix (AJM) is designed to serve as the flapless pitch control surface. The AJM consists of four control groups composed in total of 48 supersonic nozzles. The AJM aims to utilize the jet flow-interaction-induced additional control moment to improve the control efficiency during atmospheric entry. A comparative research method is employed to study the eight simulation cases for three different HFV configurations (baseline, mechanical control surface with 30° deflection, and the AJM configuration) and two AJM control moment adjustment strategies (nozzle chamber pressure regulation and discretized nozzle group on–off control). A conventional in-house computational fluid dynamics (CFD) solver with the two-equation SST turbulence model is employed to undertake the simulation tasks. Simulation results indicate that: (a) only the AJM configuration is capable of trimming the HFV in pitch channel; (b) nonlinearity exists between the augmentation moment and the specific control variable from respective adjustment strategies; (c) the chamber pressure regulation strategy bears higher overall efficiency, while the discretized control strategy induces more intense local jet-flow interaction. With a maximum control moment augmentation of 1.58, the AJM presents itself as a competitive candidate for future HFV flapless control methods.

Bayesian uncertainty analysis of SA turbulence model for supersonic jet interaction simulations

The Reynolds Averaged Navier-Stokes (RANS) models are still the workhorse in current engineering applications due to its high efficiency and robustness. However, the closure coefficients of RANS turbulence models are determined by model builders according to some simple fundamental flows, and the suggested values may not be applicable to complex flows, especially supersonic jet interaction flow. In this work, the Bayesian method is employed to recalibrate the closure coefficients of Spalart-Allmaras (SA) turbulence model to improve its performance in supersonic jet interaction problem and quantify the uncertainty of wall pressure and separation length. The embedded model error approach is applied to the Bayesian uncertainty analysis. Firstly, the total Sobol index is calculated by non-intrusive polynomial chaos method to represent the sensitivity of wall pressure and separation length to model parameters. Then, the pressure data and the separation length are respectively served as calibration data to get the posterior uncertainty of model parameters and Quantities of Interests (QoIs). The results show that the relative error of the wall pressure predicted by the SA turbulence model can be reduced from 14.99% to 2.95% through effective Bayesian parameter estimation. Besides, the calibration effects of four likelihood functions are systematically evaluated. The posterior uncertainties of wall pressure and separation length estimated by different likelihood functions are significantly discrepant, and the Maximum a Posteriori (MAP) values of parameters inferred by all functions show better performance than the nominal values. Finally, the closure coefficients are also estimated at different jet total pressures. The similar posterior distributions of model parameters are obtained in different cases, and the MAP values of parameters calibrated in one case are also applicable to other cases.

Study of the vortex structure of a subsonic jet in an axisymmetric transonic nozzle

The jet interaction flow field generated by a subsonic circular jet exhausting into a transonic cross-flow over a convergent–divergent nozzle is investigated using numerical simulations. The simulations use the three-dimensional large eddy simulation and Reynolds-averaged Navier–Stokes equations coupled with the standard k-ε turbulence model. The numerical method is verified via cold-flow and schlieren experiments. The vortex structures are identified via the Liutex–Omega method, and the flow details of various pressure ratios and injection angles are studied. The numerical results capture the main vortex structures of a jet in cross-flow, such as the trailing upper vortex and trailing major vortex. The trailing top vortex, which is difficult to capture, and a new vortex structure, named the longitudinal shear vortex, are both observed when the momentum flux is sufficiently large. This study identifies the longitudinal shear vortex for restricted flow, which to some extent facilitates the mixing of the cross-flow and the jet. The results presented in this paper indicate that the vortex structure distribution of a subsonic jet and transonic cross-flow in the restricted region can be optimized. The main vortex structures are analyzed in detail.

Sensitivity analysis of flowfield modeling parameters upon the flow structure and aerodynamics of an opposing jet over a hypersonic blunt body

Implementation of an opposing jet in design of a hypersonic blunt body significantly modifies the external flowfield and yields a considerable reduction in the aerodynamic drag. This study aims to investigate the effects of flowfield modeling parameters of injection and freestream on the flow structure and aerodynamics of a blunt body with an opposing jet in hypersonic flow. Reynolds-Averaged Navier-Stokes (RANS) equations with a Shear Stress Transport (SST) turbulence model are employed to simulate the intricate jet flow interaction. Through utilizing a Non-Intrusive Polynomial Chaos (NIPC) method to construct surrogates, a functional relation is established between input modeling parameters and output flowfield and aerodynamic quantities in concern. Sobol indices in sensitivity analysis are introduced to represent the relative contribution of each parameter. It is found that variations in modeling parameters produce large variations in the flow structure and aerodynamics. The jet-to-freestream total-pressure ratio, jet Mach number, and freestream Mach number are the major contributors to variation in surface pressure, demonstrating an evident location-dependent behavior. The penetration length of injection, reattachment angle of the shear layer, and aerodynamic drag are also most sensitive to the three crucial parameters above. In comparison, the contributions of freestream temperature, freestream density, and jet total temperature are nearly negligible.

Numerical Investigation of Interaction of Counter Flow Jet and Hypersonic Capsule Flow Via Modified DsmcFoam

Abstract In this work, numerical investigation of interaction of counter flow jet and hypersonic re-entry capsule flow has been carried out through modification of DsmcFoam solver. The DsmcFoam modification includes implementation of variable soft sphere (VSS) collision model for more accurate collision model, adjustment of nonuniform initial condition for faster convergence and nonuniform boundary condition, calculation of local Knudsen number in postprocessing for adaptive grid generation, and implementation of different gas species for multigas flow interaction simulations. Therefore, the modified DsmcFoam can be used for investigation of the effect of counter flow jet on the vehicle aerodynamics and aerothermodynamics. New validation test cases from Von Karman gas dynamics facility (VKF) tunnel data of Apollo and blunt-cone re-entry geometries are studied via DsmcFoam in which a suitable agreement of results is observed compared to experimental data and also MONACO code computations. Also, the influence of counter flow jet has been presented, i.e., changing of bow shock configuration and its distance from the vehicle. Consequently, it is observed that by increasing counter flow jet velocity or density, reduction of the drag coefficient and heat flux on the vehicle will occur. Furthermore, variation of the velocity or density of counter flow jet leads to different jet-flow interaction patterns which are presented evidently.

Numerical Investigation of Jet Interactions for a Lateral Thrust Jet Controlled Interceptor Operating at Medium Altitudes

Lateral thrust jets exhibit better maneuverability performance than control surfaces such as conventional fins for attitude control or the orbital transfer of guided weapons. In the supersonic region, however, jet interaction phenomena occur due to the lateral thrust jet during flight and a complicated flow structure is exhibited by the interaction of the shock wave, boundary layer flow, and vortex flow. In particular, hit-to-kill interceptors require precise control and maneuvering; therefore, it is necessary to analyze the effect of the jet interaction flow. A number of conventional jet interaction analyses have been performed under low-altitude conditions; however, there are not many cases with respect to medium-altitude conditions. Unlike low-altitude conditions, jet interaction flows at medium-altitude conditions have different flow characteristics. In this study, a jet interaction flow analysis is performed on a lateral thrust jet controlled interceptor operating at medium altitudes. Based on the results, the characteristics of the flow structure and the changes in the aerodynamic coefficients are analyzed.

중고도에서 운용되는 측 추력 제어 요격체에 대한 제트 간섭 유동 분석

측 추력 제트는 유도무기의 자세제어 및 궤도 천이 기동을 하는 데 있어 기존의 핀과 같이 제어 면을 이용한 방식보다 우수한 기동성을 갖는다. 하지만 초음속 영역에서 비행 시측 추력 제트로 인한 제트 간섭 유동이 발생하며 충격파와 경계층 유동, 와류 유동의 상호작용으로 인해 매우 복잡한 유동 구조를 나타낸다. 특히 직격 파괴(hit-to-kill) 방식의 요격체의 경우 정밀한 제어 및 기동이 요구되기 때문에 제트 간섭 유동이 미치는 영향에 대한 분석이 필요하다. 기존의 제트 간섭 해석은 저고도 운용 조건에서 주로 수행되었으나 중고도 운용 조건의 경우 해석 사례가 많지 않으며 대기 조건으로 인해 분사 제트 유동이 상대적으로 크게 발달하는 특징을 갖는다. 본 연구에서는 중고도에서 비행하는 요격체 형상에 대해 받음각 조건에 따라 제트 간섭 유동 해석을 수행하였다. 해석 결과를 바탕으로 유동장의 구조적인 변화 특성을 분석하였으며, 공력 계수의 변화를 비교하였다.

Numerical study on lateral jet interaction in supersonic crossflows

This paper presents numerical analyses of lateral jets in supersonic cross flows on a flat plate and on a generic missile. The freestream Mach number is 4 for the flat plate and 3 for the missile, and the jets are sonic for both cases. The numerical results are validated with wind tunnel data such as Schlieren images and surface pressure distributions. The flow structure due to the jet interaction with the supersonic free-stream is examined in terms of the vortex structure. A 3-dimensional compressible RANS solver is used for the study. To describe the effects of high temperature, a thermally perfect gas is assumed. When high temperature is applied, the shock structure changes, which affects the separation region and recirculation zone. Next, the effects of turbulence models on the jet interaction flow are investigated. The Spalart–Allmaras, Menter's shear-stress transport k–ω, Huang and Coakley's k–ε, and Coakley's q–ω models are used to analyze the flows. The differences in pressure distribution among the turbulence models are larger in the case of the flat plate than the missile. In addition, several numerical flux functions are compared to investigate their effects on the jet interaction: the Roe scheme with Sanders's H-correction, RoeM scheme, and the HLLE scheme. Although the HLLE scheme shows a little difference at the indent of the barrel shock, the three numerical flux schemes give similar CP distributions on the wall.

Hemodynamics Characteristics of a Four-Way Right-Atrium Bypass Connector

Currently, the surgical procedure followed by the majority of cardiac surgeons to address right ventricular dysfunction is the Fontan procedure, which connects the superior vena cava and inferior vena cava (IVC) directly to the left and right pulmonary arteries (LPA and RPA, respectively) bypassing the right atrium. The goal of this study is to develop a patient-specific four-way connector to bypass the dysfunctional right ventricle and augment the pulmonary circulation. The four-way connector was intended to channel the blood flow from the inferior and superior vena cava directly to the RPA and LPA. By creating a connector with proper hemodynamic characteristics, one can control the jet flow interactions between the inferior and superior vena cava and streamline the flow toward the RPA and LPA. The focus for this study was on creating a system that could identify the optimal configuration for the four-way connector for patients from 0 to 20 years of age. A platform was created in ANSYS that utilized the design of experiments (DOE) function to minimize power-loss and blood damage propensity in the connector based on junction geometries. It was confirmed that as the patient's age and artery size change, the optimal size and shape of the connector also changes. However, the corner radius did not decrease at the same rate as the opening diameters. However, it was found that power losses within the connector decrease, and average and maximum blood traversal time through the connector increased for increasing opening radius.

Turbulence statistics and distribution of turbulent eddies for jet flow and rigid surface interaction

The behavior of turbulent eddies within the self-similar region of a rigid surface interacting round jet is experimentally investigated. Results show that the turbulent jet flow structure is significantly affected due to the rigid surface interaction; particularly within the lower portion of the jet shear layer. It is observed that the jet and rigid surface interactions rather enhance the scale of axial velocity fluctuations within the intermediate region of the jet. An additional mixing layer is observed in the lower shear layer region close to the rigid surface due to the production of eddies from the rigid surface. The depth of penetration of the fluctuating eddies decreases significantly at the mixing layer region and this mixing layer acts like a shield which restricts the downward propagation of fluctuating eddies from the plane of symmetry of the jet. The results suggest that the region below the mixing layer can be treated as the shear less mixing region. The interesting consequence of this is that the rate of production of vorticity is enhanced below the mixing layer close to the rigid surface. Also, the enstrophy destruction is favored over enstrophy production at the upper portion of the mixing layer, and exactly the opposite phenomenon is observed in the lower portion of the mixing layer.

Simulation of the Supersonic Starting Jet Flow Interactions with a Rigid Body

Simulation of the Supersonic Starting Jet Flow Interactions with a Rigid Body

A New Gaskinetic Model to Analyze Background Flow Effects on Weak Gaseous Jet Flows from Electric Propulsion Devices

Recent work on studying rarefied background and jet flow interactions is reported. A new gaskinetic method is developed to investigate two closely related problems. The first problem is how a collisionless background flow can affect a highly rarefied jet flow. The rarefied jet and background flow conditions are assumed available and described with seven parameters. Gaskinetic theories are applied and formulas are obtained for the mixture properties. Simulations are performed to validate these expressions, and excellent agreement is obtained. The second problem is to recover the collisionless background and jet flow parameters with limited measurements. A group of linearized equations are derived for the flowfield properties. The solving process includes initial estimations on the seven parameters, followed with iterations. Numerical tests are performed and the results indicate the procedure is accurate and efficient. The new method and expressions can reduce the amount of experimental work and numerical simulations to analyze facility effects. Parameter studies with particle simulations may require several months; however, the new methods may require minutes. These methods can be used to quantify and predict jet performance, vacuum chamber designs and optimization. Applications may be for many societies using vacuum conditions.

Experimental study on underwater supersonic gas jets in water flow

The objective of this study is to investigate the flow structure of underwater supersonic gas jets in water flow. Supersonic gas jets submerged in a liquid flow field is experimentally studied in a water tunnel. In the experiments, a high speed camera system is used to observe the evolution of the gas jet bubble, and a dynamic pressure measurement system is used to measure the pressure fluctuation under different flow velocities simultaneously. We seek to study the mechanism of the vortex structure and the pressure fluctuation phenomenon during the gas jet evolution. The obtained results conclude that the main body formation and the pressure fluctuation of the gas jets depend heavily on the ambient flow speed. The instantaneous patterns of gas jets remarkably go upward due to the gravity effect in the still water. A shear vortex will be formed by jet-flow interaction when the ambient fluid flows. Larger vortexes are formed when the main body of the jet evolves downstream and mixes with the jet shear layer. The evolution pattern and pressure fluctuation characteristics of the gas-liquid interface are educed through a detailed analysis of the shear layer vortex structure. Backward reflection of pressure fluctuation is formed accompanying the jet bulging, necking, and back-attack. Consequently, the pressure fluctuation is transferred to the fluid at the nozzle surface and the test section. The pressure measurement system is used to confirm the pressure fluctuation phenomenon. Two measuring positions are set, i.e., pressure transducers are embedded at the nozzle surface and the test section. The pressure fluctuation with magnitude of 10 kPa is measured by the nozzle surface transducer in still water. The pressure fluctuation induced by the gas jets near the nozzle exit disappears simultaneously when the ambient fluid flows. However, the amplitude of pressure fluctuation decreases at the nozzle surface but increases at the test section with the increasing flow velocity. Power spectrum analysis is carried out and shows that the mechanical energy of the water tunnel gas jets is mainly distributed in the frequency band of 0-700 Hz. A jet induced large pressure fluctuation with a dominant frequency about 200 Hz can be captured near the nozzle surface in still water. With increasing water velocity, the dominant frequency of the unsteady pressure fluctuation decreases significantly at the nozzle surface. Conversely, the flow velocity leads to an increase in the spectral intensity of the pressure at the test section.

Some influence factors in aerodynamic heat transfer numerical simulation of jet-interaction flow

Some influence factors in aerodynamic heat transfer numerical simulation of jet-interaction flow

Numerical studies on the separation performance of liquid- liquid Hydrocyclone for higher water-cut wells

Liquid-liquid hydrocyclones have nowadays become very useful in the oil industry because of their numerous applications. They can be installed downhole in the case of a well that produces higher water-oil ratios. The design of a liquid-liquid hydrocyclone for such a task is critical and every geometric part of the hydrocyclone has a part to play as far as separation is concerned. This work, through validated numerical technique, investigated the liquid-liquid hydrocyclone performance for the cases of single-inlet and dual-inlets, with different upper cylindrical lengths, specifically, 30mm and 60mm.It was observed that the hydrocyclones with the 30mm upper cylindrical section perform better than the ones with 60 mm upper cylindrical section. It was again noted that, even though higher number of tangential inlets increases the swirl intensity, they have the tendency to break up the oil droplets within the hydrocyclone because of increasing shear and jet flow interaction.

Twin Jet Interaction and Reverse Flow

Starting characteristics of the underexpanded twin jets and reverse flow as a consequence of interaction at high altitudes were experimentally investigated in a High Altitude Jet Simulation Facility. The flowfield characteristics were captured through Schlieren flow visualization. Pitot pressure survey upstream of the jet inflection point showed the existence of reverse flow due to jet interaction. The nature of the reverse flow at higher pressure ratios, in the vicinity of the jet inflection point was supersonic and become lower subsonic near the base. On the other hand, at lower pressure ratios, the reverse flow was subsonic throughout the base region. The reverse-flow Mach number was dictated by the dissipation effect and the vented area shape in the base region. Base pressure measurements confirmed that reverse flow was fully diffused at the base.

Numerical investigation of lateral jet interaction effects on the hypersonic quasi-waverider vehicle

Numerical simulations are carried out to investigate lateral jet interaction effects for the hypersonic quasi-waverider vehicle. A reasonable jet nozzles layout is proposed. Based on three-dimensional viscous compressible Reynolds Averaged Navier-Stokes codes, comparisons of the jet interaction flow structures between quasi-waverider vehicle and general axisymmetric vehicle are conducted. Furthermore, the effects of lateral jet control are examined for different angles of attack and free-stream Mach numbers. From detailed flow structure and pressure distribution analysis, the quasi-waverider vehicle gets a better effect of lateral jet without “wrap-around” the body. With the increase in angle of attack or free-stream Mach number, the attitude control moment reduces and the effect of lateral jet decreases.