Lateral Jet Research Articles

Hypersonic flow characteristics and relevant structure thermal response induced by the novel combined spike-aerodome and lateral jet strategy

Huge aerodynamic drag and severe aeroheating are the inevitable challenges for hypersonic vehicles, this paper proposes a novel combined spike-aerodome and lateral jet strategy for drag reduction and thermal protection. Meanwhile, the hypersonic flow characteristics and structure thermal response are numerically investigated by an in-house code. The obtained results demonstrate that this novel strategy not only further reduces the total drag, but also provides excellent thermal protection for both the blunt body and spike rod. Then the effects of lateral jet pressure ratio, spike length and aerodome diameter on the flow properties, drag and heat reduction performance are thoroughly explored. Increasing the lateral jet pressure ratio can effectively enhance the thermal protection. Surprisingly, in a certain range, higher lateral jet pressure ratio even leads to larger pressure peak value on the blunt body. Increasing the spike length would enhance the heat transfer along the blunt body surface, and the total drag changes non-monotonically as the spike length varies. The total drag rises significantly when the aerodome diameter increases, and it can be increased by 40.1% when the aerodome diameter ratio increases from 0.15 to 0.5. Besides, increasing the aerodome diameter is beneficial to remarkably enhance thermal protection.

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.

Thermal performance of radially rotating trapezoidal channel with impinging jet-row

The detailed Nusselt number distributions and Fanning friction factors of the rotating trapezoidal channel cooled by a row of six in-lined impinging jets were measured. The channel orientation relative to the rotating axis was 45 degrees and the six lateral jets issued from a plenum chamber were aimed at the centerline of the apex wall of the trapezoidal channel. The experimental conditions in terms of channel Reynolds (Re), rotation (Ro) and buoyancy (Bu) numbers were 5000–17500, 0–0.3 and 0–0.088, respectively. Also the rotational impact on the mass flow rate through each nozzle was examined. The coupled and isolated effects of Coriolis force and rotating buoyancy on the thermal performance of the rotating channel were illustrated using a selective set of test results. Due to the Coriolis-force effect on the radially outward crossflow and the impinging jets, the airflow rates issued from the jets 1–3 and 5–6 were respectively increased and decreased from the non-rotating values. With the different degrees of Ro impact on the leading, apex and trailing walls of the rotating trapezoidal channel, the Coriolis force effect on the heat transfer distribution was spatially asymmetric. The present “cavity-like” channel hub configuration significantly undermined the fluency of the spent flow to incur weak convection region adjacent to the sealed channel hub. But the Coriolis force effect considerably improved the heat convection over the channel hub region. All the Nusselt number ratios between the rotating (Nu) and non-rotating (Nu0) channels followed the general pattern of hub-to-tip decay. While the rotating buoyancy effect impaired the heat transfer performance, its impact was systematically weakened when the relative strength of Coriolis force enhanced. Two sets of empirical correlations that permitted the evaluations of the regionally averaged Nusselt number over the leading, apex and trailing walls and the overall Fanning friction factors were devised to assist the development of an internal cooling scheme of a gas turbine rotor blade.

Evidence for a Bright-edged Jet in the Optical/Near-infrared Afterglow of GRB 160625B

Abstract Using deep and high-cadence gamma-ray burst (GRB) afterglow data from the Reionization And Transients Infra-Red/Optical camera, we observe a sharp and achromatic light curve break 12.6 days after the GRB, accompanied by an approximately achromatic bump. Fitting of the optical, near-infrared, and X-ray data suggest a very narrow (2°) jet that remains collimated at late time. We argue that the sharp light curve bump suggests an edge-brightened jet, perhaps emitting only during a brief period of lateral jet expansion. The light curve also exhibits a gradual spectral evolution lasting >10 days. The evolution of the flux can be modeled as , with a temporal slope α = −0.956 ± 0.003 and a gradually time-varying spectral slope .

Intermittent round jet controlled by lateral pulse-modulated synthetic jets

A round air jet was actively controlled by a pair of lateral control jets. The control jets were generated by a pair of opposing synthetic jet actuators, which were driven by the pulse-modulated sinusoidal signal. Two carrier frequencies were tested, namely 160 Hz and 840 Hz. Moreover, control jets driven by un-modulated sinusoidal signals were also tested. An unforced continuous jet was used as the reference case, and for all cases, the Reynolds number of the main round jet was 1570 (related to the nozzle exit diameter of 10 mm). Experiments (flow visualization and hot-wire anemometry) revealed that the flow control caused a suppression of the jet core and a more rapid jet flow decay. In addition, the pulse modulation caused jet intermittency that was distinguished by the periodicity of the time-averaged and fluctuating velocity components. For the case of the lower carrier frequency of 160 Hz, a flapping motion of the controlled jet occurred and the jet formed a zigzag pattern.

PIV Experimental Study on Flow Field near Lateral jet under the Condition of Vegetation

The high-frequency PIV was applied to measure the flow field near the lateral jet under the condition of rigid vegetation and flexible vegetation. Both the Single row vegetation and broadleaf grass were analyzed. The results showed that different vegetation arrangements have different effects on the jet flow field. The vegetation arrangement and vegetation resistance cause significant changes. The changes in flow velocity with changes in water depth displayed “S” type and anti-“S” type distributions, and the flow velocity of free layer was approximately logarithmic. Due to vegetation resistance and jet pressure differences, the lateral jet trajectory in water with vegetation also have different distributions. The lateral jet trajectory in water with broadleaf grass was more likely to bend than in water with rigid vegetation Compared to the influence of two vegetation arrangements on the water flow near the jet, the flexible vegetation has a better deceleration effect on the flow field near the lateral jet.

Model free active flow control of a simplified car model

Abstract A model free control (MFC) approach is presented and used to symmetrize the unstable wake flow of a simplified car model named Ahmed body. Such unstable phenomena with regards to the space-time evolution of the low pressure wake vortex core, is known to increase the global drag of square back vehicles. Results highlight the ability of a MFC to reduce the wake symmetry breaking phenomena by using lateral blowing slit jets. A model free control scheme derived from (Fliess and Join, 2013) is proposed and a tuning procedure is suggested. At last experimental results on an Ahmed body in wind tunnel are provided.

Analysis of an improved trajectory correction scheme based on mass blocks

In conventional technical trajectory correction schemes, continuous attitude adjusting mechanisms, such as canards, are inferior in terms of response time and efficiency of executing instructions. Discontinuous attitude adjusting mechanisms, such as the lateral pulse jet, have complex impact on the airflow layer of the projectile surface caused by the thrust vector jet flow. An improved two-dimensional trajectory correction mechanism is designed based on the principle of firing mass blocks by a tailor-made propellant. The mechanical properties of the thrust force (namely the correction force) is analyzed. The trajectory correction model is established to analyze the effects of correction starting moment and correction phase angle of a thrust force on the projectile's trajectory. According to the trajectory correction scheme, an improved genetic algorithm is employed to this work. The scheme is tested in the simulation. The results show that the correction scheme is effective to reduce target dispersion and increase the precision of the impact point.

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.

Coupled investigation on drag reduction and thermal protection mechanism induced by a novel combinational spike and multi-jet strategy in hypersonic flows

Drag and heat reduction strategy in hypersonic vehicle design has already attracted worldwide attention. In this paper, a novel combinational spike and multi-jet strategy has been proposed for the drag and heat reduction in hypersonic flows. The flow field induced by this novel strategy has been numerically investigated by an in-house code. High-resolution upwind scheme (AUSMPW) and SST k-ω turbulence model are employed in the code. The fluid-thermal interaction is considered by using the conjugate heat transfer (CHT) approach. In addition, the thrust produced by the opposing jet is taken into account in computing the total drag. The influences of the spike length-to-diameter ratio, jet pressure ratio and lateral jet location on the flow field, drag reduction and heat properties are investigated thoroughly. The numerical results reveal that this novel strategy has better drag and heat reduction efficiency of unit mass flow rate, and the negative thrust induced by the opposing jet proved to be an important factor for the total drag. The spike length-to-diameter ratio has a great influence on the drag reduction, and the drag coefficient decreases significantly as the spike length-to-diameter ratio increases. However, the Stanton number is less affected by the spike length-to-diameter ratio variation. The jet pressure ratio, including the pressure ratios of opposing jet and lateral jet, are the key parameters for the drag reduction and thermal protection, and both the drag coefficient and the Stanton number decrease significantly as jet pressure ratio rises. For the lateral jet location effect, it influences the flow features, drag reduction and thermal protection significantly. The drag coefficient can be reduced by nearly 20% as the lateral jet location increases from 0.1 to 0.7, and the peak value of the Stanton number increases sharply by 49.36% when the lateral jet location varies from 0.9 to 0.1.

Novel Combinational Aerodisk and Lateral Jet Concept for Drag and Heat Reduction in Hypersonic Flows

Hypersonic vehicles have attracted lasting and worldwide attention in recent years. Considerable aerodynamic drag and severe aerothermal loads are major challenges for hypersonic vehicles. A novel combinational aerodisk and lateral jet concept is proposed for drag reduction and thermal protection in hypersonic flows. The flow field characteristics have been numerically investigated with in-house code. The Reynolds-averaged Navier-Stokes (RANS) equations were adopted to simulate the flow field, and the shear stress transport (SST) k−ω turbulence model was used to present the turbulent nature. Fluid–thermal interaction is also taken into consideration in this paper. The influences of the lateral jet pressure ratio and its location on the flow field have been thoroughly studied using numerical methods. The obtained results demonstrate that the novel concept is beneficial for drag reduction and thermal protection in hypersonic flows. Increasing the lateral jet pressure ratio can further improve drag reduction performance. In addition, the heat flux can be significantly reduced by increasing the lateral jet pressure ratio. The lateral jet location also has important effects on the flow properties. The peak values of the Stanton number and wall static pressure can even be reduced by 19.76% and 22.15%, respectively, with different lateral jet locations.

Effect of a Lateral Jet on the Turbulent Flow Characteristics of an Open Channel Flow with Rigid Vegetation

Aquatic vegetation can purify polluted bodies of water and beautify the environment, as well as alter the structure of water flow and affect the migration and diffusion of pollutants in bodies of water. Vegetation can significantly change the original water flow, especially in cases in which aquatic vegetation interacts with a jet. Characteristics of jet flow open channels without vegetation have been studied, but research on the characteristics of open-channel flows under the action of lateral jets and in the presence of vegetation are rare. High-frequency particle image velocimetry (PIV) was used to measure a lateral jet in water with rigid vegetation and our results were compared to the lateral jet flow field in water without vegetation. The results show that the vegetation arrangement and vegetation resistance cause significant changes. The presence of vegetation increased the surface velocity of the water, and the flow velocity decreased in the interior area of the vegetation and near the bottom of the water tank. The changes in flow velocity with changes in water depth displayed “S” type and anti-“S” type distributions, and the flow velocity of free layer was approximately logarithmic. Due to vegetation resistance and jet pressure differences, the lateral jet trajectory in water with vegetation was more likely to bend than in water without vegetation. The turbulence intensity and Reynolds stress had different distributions for water with and without vegetation. At the top of the vegetation and near the water surface, turbulent mixing of the water flow was strong, the flow velocity gradient was large and the turbulence intensity and the Reynolds stress reached their maxima. The effects of a lateral jet on an open-channel flow were compared for different vegetation conditions, revealing that a rhombic vegetation arrangement has a stronger deceleration effect than other arrangements. The theoretical results can be applied to wastewater discharge into vegetation channels.

An experimental study of binary lateral jets on a standard model in subsonic, transonic, and supersonic cross-flows

There are numerous aerodynamic and nonaerodynamic methods to control flying devices, one of which is lateral jets, i.e. a high-speed method with convenient operation at low speeds or high altitudes. In this research, a new arrangement of lateral jets is examined by testing in a wind tunnel. The test is conducted on the Basic Finner model. In this design, the jets at the top and bottom of the model are arranged in pairs and parallel to each other. This combination, in addition to controlling pitch channel, provides the necessary conditions to control the roll channel. In this paper, pressure distribution is examined in the upstream and downstream areas as well as middle of jets. The flow visualization method is also used. The results are provided for subsonic, transonic, and supersonic free flow regime at the positive and negative angles of attacks. In the subsonic and supersonic flows, the achievements of the binary jets are the further pressure reduction on the middle line of jets compared with the same position at downstream of a single jet, and maintaining a high-pressure area of a single jet at the upstream of jets compared with the upstream area. However, the pressure reduction rate is lower in the transonic regime and the effectiveness of the angle of attack is greater than the subsonic and supersonic flows. Finally, a comparison with numerical result is accomplished.

Slam Loads and Kinematics of Wave-Piercing Catamarans During Bow Entry Events in Head Seas

Centre bow (CB) design for wave-piercing catamarans (WPCs) is a critical compromise between minimization of slamming and protection against deck diving. To inform the design process, this article investigates the slam loads and kinematics during bow entry events in regular head seas for a 112-m WPC with systematic variations to its CB and wet-deck geometry. Model tests using a 2.5-m hydroelastic segmented catamaran considered five different CB configurations, designated as the parent, high, low, long, and short CB. The results indicated that changes in the CB length had little effect on the general kinematic trends obtained for the pitch, heave, and bow vertical displacement at the instant of slamming, but increasing the wet-deck height resulted in an increase in heave (but not pitch) at slamming. Two new design ratios are proposed. The CB immersion depth to arch height ratio showed slamming occurring in the range of 0.3–0.6 depending on the wave encounter frequency and the CB configuration. The CB buoyancy in the encountered waves was estimated by considering both immersion depth and area along the CB in waves through relative motion analyses. It was found that the buoyancy to slam force ratio increased with increasing wet-deck height but not with increasing CB length. This suggests that an optimal CB configuration could be achieved by first modifying the arched cross-structure to reduce the arch filling effect on slamming severity and then maximizing the CB buoyancy to slam force ratio by increasing either the wet-deck height or the CB length. 1. Introduction An above-water centre bow (CB) for improving seakeeping is a feature of modern wave-piercing catamarans (WPCs) (Soars 1993; Boulton 1998; Fang & Chan 2007; Dubrovsky 2014). Figure 1 shows a 112-m Incat WPC with the CB located between the two demihulls. There are several important factors to be considered when designing such a central bow. First, the reserve buoyancy offered by the CB is the primary design factor for providing a pitchrestoring moment and eliminating deck diving in the following waves (Davis & Whelan 2007). Second, the CB configuration can influence the slamming loads in WPCs during bow entry in waves (Lavroff et al. 2013). This is due to the complex fluid-structure interaction in the CB area. When the CB enters waves, the water gradually fills the spaces between the CB and demihulls, referred to here as archways, and may result in complete closure of the archways and slamming in excessive pitch conditions. Finally, the frequency of slamming occurrence is, to some extent, related to the CB design as it contributes to lateral jet flow during the CB entry. As a result, slamming may occur in even partial water entrapment below the arch wet-deck cross-structure, which could be the case in small pitch motions (Lavroff & Davis 2015).

Study on draining off water mechanism and interaction characteristic of high-temperature and high-pressure combustion-gas jets with the water

A new method of underwater launching is proposed to overcome the water resistance in the barrel and realize continuous launching by forming gas curtain without any complex device. Namely, part of gunpowder combustion-gases behind the projectile is guided to the space in front of underwater projectile by opening pores around the circumference of the warhead, to form a dry launching path. Based on this, the expansion process of combustion-gas jets in the confining tube filled with water, especially complex interaction of high-pressure and high-temperature combustion-gas jets and water is studied by experiments and numerical calculations. The results show that, when the high-velocity combustion-gases inject into motionless liquid environment, multiple Taylor cavities are formed and typical structure of Taylor cavity presents two parts, including bubble head and combustion-gas path. The distribution of the recirculation zone is an important factor for the flow field structure and the effect of draining off water. The recirculation zone of the central jet expands downstream with time going on and is decreasing until it disappears. While, the recirculation zone of lateral jet is strengthening with developing downstream. In the whole expansion process, lateral combustion-gas jet plays a significant role on radial expansion process of Taylor cavities.

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.

The influence of coolant jet direction on heat reduction on the nose cone with Aerodome at supersonic flow

Reduction of aerodynamic heating is a critical issue for the development of the hypersonic vehicles. In this study, a computational fluid dynamic is applied to study the effect of location of coolant jet in the vicinity of the aerodome on the heat reduction of the nose cone at M = 5. In addition, the influence of the gas types (Air, He and CO2) on the cooling performance is investigated. This research mainly focused the flow feature and mass distributions of various coolant jets. In order to study these effects, a two-dimensional model with spike is chosen to simulate the various shocks in the vicinity of the nose cone. The effect of significant parameters is studied by using the Reynolds-averaged Navier–Stokes equations with Menter's Shear Stress Transport (SST) turbulence model. Results show that the injection of the coolant gas from the top of aerodome significantly decreases the heat load on the nose cone. In addition, injection of the coolant jet from the top is more efficient on the recirculation region on the top of spike. The obtained results reveal that the injection of coolant from the front of the aerodome does not reduce the heat load substantially. In addition, the cooling performance of helium jet as the lateral jet is 15% more than other gases.

Tunable Droplet Breakup Dynamics on Micropillared Superhydrophobic Surfaces.

Functional materials with controllable droplet breakup properties have extensive application prospects in aircraft anti-icing, spraying cooling, surface coating, and so on. Here we show that introducing micropillar arrays with various morphologies to fabricate superhydrophobic surfaces could either facilitate or suppress droplet splitting. The spacing and height of micropillars play an essential role in tuning the splitting patterns. Delayed splashing occurs on dense pillars which support the liquid lamella and provide channels for air to escape. A novel droplet breakup mechanism is found on sparse tall pillars, which rises from the instability of lateral liquid jets and significantly reduces the droplet breakup threshold. The critical Weber number of the rupture of low-viscous liquid is solely determined by the geometric parameters of micropillars and droplets. This work unveils the impact of ordered microstructures on the droplet breakup dynamics and provides a quantitative analysis of the geometric parameters in revising the breakup criteria.

Numerical Investigation of Lateral Jet with Supersonic Reacting Flow

To improve the understanding of the lateral jet, this paper reports the computational fluid dynamics simulations of a cone–cylinder–flare model with lateral jet control, especially with regard to the interaction of a cold- or hot-gas jet with a supersonic crossflow. The Spalart–Allmaras turbulence model is used to solve the three-dimensional compressible Navier–Stokes equations, and the methodology is first validated by comparing the numerical results with the wind-tunnel data. The predicted axial pressure coefficient profiles are acceptably accurate with the experimental data. However, in the case of a hot-gas jet without considering the chemical reaction, there is a significant error at the separation point compared with the experimental result. Using a simplified reaction mechanism, the chemical reaction is carried out in the hot-gas jet simulation. The numerical results show that the separation of the boundary layer takes place at a distance of eight times of the nozzle diameter, which is very close to the experimental result. The aforementioned results indicate that, in the simulation of lateral jet interference, it is necessary to consider the chemical reaction, which can improve the numerical accuracy of predicting both the aerodynamics performance and flow structures.

Application of a modified pseudopotential lattice Boltzmann model for simulation of splashing phenomenon

In this study, a two dimensional modified pseudopotential single-component multiphase lattice Boltzmann model is utilized to simulate impingement of single and double droplets on both stationary and moving liquid films. The model is confirmed to be accurate according to the power law in terms of crown spreading. In addition, coexistence densities at both liquid and gas phases are compared with densities, obtained by Maxwell analytical solution. The effects of the Reynolds number, Weber number, Bond number, liquid film thickness, and wall interactions with liquid film for the case of single droplet are individually investigated. The results prove that the enhancement of liquid film thickness postpones the droplet break-up on the crown’s free edge. It is also found that, the hydrophobic surface abates the splashing mechanism due to the existing repulsive force between wall and liquid film. Simulation of splashing phenomenon inside a slit indicates that the crown formation follows the rectangular and curvature shape of the slit. The simulation is also carried out for two droplets with horizontal and vertical arrangements. For the horizontal arrangement, the crown is divided into central and lateral regions. In comparison with lateral jets, crown’s central jet is higher. Furthermore, droplets’ vertical arrangement elevated the cross section of the crown’s free edge, therefore the secondary droplets do not form in this condition. Up to the end of this study, the effect of the bottom moving wall on the binary droplet impact is examined, and it is found that by increasing the moving wall’s velocity, the crown height at the central region and the downstream side abates. Moreover, the effect of moving wall at the upstream side is different, and the splashing mechanism can be either suppressed or enhanced at this side. In fact, the moving wall performance at the upstream depends on the impact conditions and the governing non-dimensional numbers.