Short Penetration Mode Research Articles

Numerical investigation of effect of the design parameters of the counter-flow jet for drag reduction in hypersonic low-Reynolds number regime

Due to the correlation of design parameters of the counter-flow jet in addition to the complexity of the flow field, understanding the mechanism of the counter-flow jet for drag reduction and flow control remains challenging. Furthermore, to satisfy the demands of the space transportation system, investigating the counter-flow jet's suitability for a range of flight conditions is critical. To solve these problems, a study was performed by varying the pressure ratio (PR) and exit Mach number of the counter-flow jet at hypersonic low-Reynolds number regime. For numerical simulations, laminar, axisymmetric Navier–Stokes equations were solved by the total variation diminishing scheme with second-order accuracy in space and the explicit strong stability preserving the Runge–Kutta method. With given numerical conditions, the flow field was categorized as the long penetration mode (LPM) based on the penetration length and the fluctuation of the flow field at the high-Reynolds number regime. By reducing the free-stream flow Reynolds number while keeping other parameters unchanged, the flow field transitioned from the LPM to a stable LPM, short penetration mode, or long penetration with periodically oscillation mode. The critical Reynolds number for the transition of the flow field is highly dependent on the exit Mach number of the counter-flow jet and PR. The extended jet layer was the primary reason for the fluctuation of the drag coefficient. Furthermore, with the counter-flow jet at certain flight conditions, drag can be reduced by up to 78% regardless of the stability of the flow field.

Investigation on the opposing jet penetration mode transition mechanism in the hypersonic flow

Abstract As an effective drag reduction and thermal protection technology, the opposing jet can guarantee the flight safety of the hypersonic vehicle. In this paper, the jet mode transition is realised by controlling the total jet pressure ratio value (PR) with a function. The jet mode transition from the long penetration mode (LPM) to the short penetration mode (SPM) uses an increasing function. However, the jet mode transition from SPM to LPM uses a decreasing function. The flow field reconstruction process of a two-dimensional axisymmetric blunt body model in the hypersonic flow is studied when the jet mode transition between SPM and LPM changes into each other. The flow field structures and wall parameters of the LPM and SPM transition processes are obtained. The results indicate that the drag and Stanton number both decrease in the transition stage from LPM to SPM, and this is beneficial for the improvement of the drag reduction and thermal protection effect. The peak values of drag and Stanton number fall by 36.39% and 46.40%, respectively. When the jet mode transforms from SPM to LPM, the Stanton number increases, and the drag force first increases and then decreases. However, the final drag reduction effect is not obvious. With the increase in the change rate of the total pressure ratio of the two jet transformation modes, the jet mode transition time is advanced, and the flow field changes more violently.

Numerical Investigation on the Thermal Protection Characteristics of a New Active Jet Design Parameter for Hypersonic Flight Vehicle

This study investigated the thermal protection performance of an active jet thermal protection system (PRsAJ-TPS) based on a new jet design parameter PRs for hypersonic flight vehicles (HFVs). The new parameter PRs is defined as the relationship between the jet flow total pressure and the free flow total pressure behind the outer bow shock. A 20° tilted nozzle design is employed together with the PRs to form the PRsAJ-TPS. Theoretical and numerical analysis is performed to prove the advantages of using the PRs. A conventional in-house CFD solver with the k ‐ ω SST turbulence model is utilized to perform the calculation. The influence of different PRs (working in the short penetration mode) and flight angles of attack on the performance of the PRsAJ-TPS is also studied. The simulation results confirmed that with a constant PRs, the Mach disk location stays the same and the normalized heat flux reduction is similar at different flight conditions. Nearly linear relationships exist between the new design parameter PRs and thermal protection performance indicators. The PRsAJ-TPS also exhibits good protection when flight angle of attack (AoA) varies between 0° and 40°, with the best results achieved at AoA = 0 ° . This study provides valuable information for the engineering application of the jet-based TPS to future HFVs.

Numerical Investigation on the Jet Characteristics and the Heat and Drag Reductions of Opposing Jet in Hypersonic Nonequilibrium Flows

We adopted the transient numerical method for the simulation of an ELECTRE vehicle with an opposing jet at an altitude of 53.3 km and 13 Ma to explore the jet characteristics as well as the performance in heat and drag reductions of the opposing jet in hypersonic nonequilibrium flows. The time-accurate, nonequilibrium N-S equations coupled with the five-species Park chemical kinetic model and vibrational energy excitation were applied, and an open source solver Hy2FOAM based on the OpenFOAM platform was adopted. Three opposing jets with different jet radii (R7 jet, R14 jet, and R21 jet) were investigated. The results show that with the increasing jet flow rate, the jet mode of the opposing jet with a small jet radius varies from the overflow mode to the long penetration mode (LPM) and finally to the short penetration mode (SPM), while that with a large jet radius directly changes from the overflow mode to the SPM. The state of the jet in the overflow mode is stable, whereas in SPM and LPM, it is unstable. The investigation of the heat and drag reductions for the R7, R14, and R21 jets shows that except for the jet in LPM, the jet in SPM and overflow mode can provide effective thermal protection, and the thermal protection is enhanced with the increasing jet flow rate. Moreover, the jet in both LPM and SPM can effectively reduce the aerodynamic drag, but the jet in overflow mode cannot provide effective drag reduction. Moreover, the jet with a large radius and in the overflow mode has a better thermal protection effect, and a small jet radius contributes to the drag reduction.

Experimental and numerical investigation on opposing plasma synthetic jet for drag reduction

Experimental and numerical studies are carried out to validate the potential of opposing Plasma Synthetic Jet (PSJ) for drag reduction for a hemisphere. Firstly, flow field changes of opposing PSJ are analyzed by comparing the experimental schlieren images and simulation results in a supersonic free stream of Mach number 3. As PSJ is a kind of unsteady pulsed jet, the shock standoff distance increases initially and then decreases under the control of PSJ, which corresponds to the change of the strength of PSJ. Accordingly, the amount of drag reduction of the hemisphere increases initially and then decreases. It is found that there is a short period of “drag rise” during the formation of PSJ before the drag reduction, which is induced by the generation of normal shock waves and the area difference of the cavity wall of PSJ Actuator (PSJA). Secondly, the effects of five parameters, including exit diameter, discharge energy of PSJA, Mach number, static pressure of incoming flow and angle of attack, on drag reduction of opposing PSJ were studied in detail by using numerical method. It is found that the Maximum Pressure Ratio (MPR) has a significant impact on the average drag reduction for a configuration-determined PSJA. For the configuration selected in this study, the flow field of opposing PSJ shows typical Short Penetration Mode (SPM) in a control cycle of PSJ when the MPR is less than 0.89. However, the flow field shows typical Long Penetration Mode (LPM) at some time when the MPR is bigger than 0.89. Relatively better drag reduction is achieved in this case.

Parametric research on drag reduction and thermal protection of blunt-body with opposing jets of forward convergent nozzle in supersonic flows

Extreme drag and aerodynamic heat are the main penalties for blunt forebody of supersonic vehicles. This results in shorter flight range and higher fuel consumption, and aerodynamic heat seriously affects the performance of internal electronics. In the current study, the flow field mechanism of a blunt body model with a supersonic opposing jet in a supersonic flow field is numerically study. The physical model is a two-dimensional axisymmetric blunt forebody model with a convergent nozzle structure, and the numerical calculation model is a coupling of the two-dimensional axisymmetric Reynolds average method and the shear stress transport(SST) turbulence model. The calculation results in this paper are compared with the experimental data in the literature, which verifies the accuracy, and the calculation verifies the grid independence. An active flow control method that controls a single pressure parameter is proposed, and the formation process of the opposing jet in the convergent nozzle is considered, and the flow field structure of the opposing jet formed by the convergent nozzle with different nozzle sizes is studied. The results show that a single pressure parameter can control the formation of a supersonic opposing jet to form a long penetration mode and a short penetration mode. The ratio of the ambient pressure to the jet pressure at the stagnation point of the blunt body can directly affect the flow field structure of the opposing jet, and reasonable control of opposing jet parameters is an effective way for thermal protection and drag reduction of blunt body structures.

Characterization of plasma synthetic jet actuator with Laval-shaped exit and application to drag reduction in supersonic flow

A plasma synthetic jet (PSJ) actuator (PSJA) with a Laval-shaped exit is investigated using a numerical method alongside a PSJA with a straight-shaped exit for comparison. The accuracy of the numerical method is first verified by comparing simulation results with experimental schlieren images and pressure measurement values. The performance of the PSJA with the Laval-shaped exit is then investigated in quiescent air. The results show that when the dimensionless energy ε > 5.06, the maximum exit velocity of the PSJA with the Laval-shaped exit becomes supersonic and is higher than that of the actuator with straight-shaped exit. The opposite is true when ε ≤ 5.06. The jet front velocity of the PSJ is much lower than the exit velocity, and no obvious improvement is seen when changing from the straight-shaped exit to a Laval-shaped exit due to the shock waves near the exit. Finally, the drag reduction effect of an opposing PSJ on a hemisphere in Ma3 flow is investigated. For a geometrically fixed PSJA, the flow field of a singled-pulsed opposing PSJ in Ma3 flow can be classified into three patterns according to the values of the maximum pressure ratio and ε: pattern 1 consists of only vortices and a slight change in the bow shock, pattern 2 consists of a typical long penetration mode (LPM) of the opposing PSJ, and pattern 3 consists of both a short penetration mode and a LPM. For PSJAs with both kinds of exits within a certain range, the average drag reduction increases with ε. However, when ε is higher than 48.02 for a Laval-shaped exit and 16.01 for a straight-shaped exit, the drag reduction effect decreases due to the rise in drag associated with the formation of the PSJ. The drag reduction effect associated with a PSJA with a Laval-shaped exit is significantly better than that of one with a straight-shaped exit when ε > 8. The optimal average drag reduction values, 25.82% and 20.55%, are obtained at ε = 48.02 and ε = 16.01, respectively, for a Laval-shaped exit and a straight-shaped exit.

Thermal protection performance of a low pressure short penetration mode in opposing jet and its application

An experiment about the flow mode of opposing jet is performed in a supersonic quiet tunnel, and a Nanoparticle-based plaser scattering method(NPLS) is used to acquire the shock wave information. A stable short penetration mode (SPM) in low jet pressure is observed in experiment aside from the traditional unstable long penetration mode (LPM) and high-pressure stable SPM. Hence, the flow mode of the opposing jet presents three kinds structures as the increasing jet pressure: low-pressure stable SPM, unstable LPM and high-pressure stable SPM. Then, numerical analysis about the flow-field and surface heat transfer on the opposing jet is conducted. The low-pressure SPM in hypersonic flow is also acquired in numerical results. Comparing to the unstable LPM, the low-pressure SPM has better cooling efficiency than the unstable LPM with smaller coolant gas. Nevertheless, the low-pressure SPM is not suitable for opposing jet TPS than the high-pressure SPM because its intensity is not strong enough to provide available thermal protection performance. The low-pressure SPM can be introduced to the combinational opposing jet and platelet transpiration TPS which the cooling efficiency in reattachment region is strengthened by transpiration coolant so the intensity of the opposing jet can be reduced to save coolant mass. The numerical results indicate that opposing jet and platelet transpiration combinational TPS with low-pressure SPM mode can realise better cooling effect and high efficiency than the traditional high-pressure opposing jet TPS.

Drag reduction analysis of counterflow jets in a short penetration mode

The characteristics around counterflow jets are difficult to predict, because of the many variables involved. To analyze counterflow jets with different freestreams, a numerical simulation was conducted, by solving a two-dimensional axisymmetric RANS equation. The trends in drag reduction were reviewed in short penetration mode, with freestream conditions (altitude: 10 to 19 km, M∞: 2.0 to 4.0). According to the results of the numerical analysis, it was determined that the differences in overall flow structure arise from the freestream Mach number. The recirculation zone is the key feature of the flow. In the flow mechanism, the recirculation zone is affected by the velocity and pressure at the boundary, and the position and pressure of the reattachment point are the main parameters influencing the recirculation zone. Observed differences in the flow structure depending on the freestream Mach number can be explained by these parameters. As a result, different drag reduction curves can be drawn for each freestream Mach number, and a maximum value on drag reduction exists.

Combination of counterflow jet and cavity for heat flux and drag reduction

In the present work, a computational study is carried out to explore the potential of a combination of a forward-facing cavity and a counterflow jet for drag and heat flux mitigation for an axisymmetric body in a supersonic free stream of Mach 2. A comparison between the axisymmetric body with a forward-facing cavity and counterflow jet and the baseline geometry without the cavity and jet is made. The first part of this study focuses on capturing the transition point of the two counterflow jet modes, Long Penetration Mode (LPM) and Short Penetration Mode (SPM), by changing the pressure ratio of the nozzle. It gave an appropriate nozzle operating pressure selection based on the design requirement. The LPM is found to be suitable when only drag reduction is required, while the SPM provides both drag and heat flux reduction, but at a higher operating jet pressure. Next, a study is conducted to characterize the effect of the angle of attack on system performance. The LPM shows improvement over the baseline geometry for only a narrow range of angles of attack, while the SPM provides improved performance for a wider range of angles of attack. The effect of cavity and cavity dimensions on performance is then studied.

Hypersonic drag reduction mechanism of a novel combinational spike and multi-opposing jets aerodynamic configuration

The shock wave drag significantly affects the aerodynamic performance of hypersonic vehicles, a novel combinational configuration is proposed to reduce the drag in this paper. The basic configurations are the spike, nose cone, front and rear jets, respectively. The numerical method is used to study the drag reduction performance. The combinational configuration has weaker reattachment shock wave than the other configurations, and both the peak pressure of nose cone and drag coefficient are decreased by more than 45%, which verifies the excellent drag reduction performance of combinational configuration. The influencing factors are analyzed in this paper. Lengthening the spike and increasing the total pressures of two jets can make the reattachment shock wave away from wall, weaken its intensity and increase the drag reduction performance. Furthermore, the change rates of wall pressure distribution of the nose cone and drag coefficient gradually decrease. When the sizes of two nozzles are small, the rear jet appears as the long penetration mode. When the sizes of two nozzles are larger than corresponding critical sizes, respectively, the rear jet will convert to the short penetration mode. Increasing the sizes of two nozzles makes the reattachment shock wave away from wall and increases drag reduction performance with the rear jet being SPM as well. The size and total pressure of front jet has greater influence on the drag coefficient. The influence of above factors on the flow characteristics and mass flow rate of nozzle is also studied in this paper.

Parameter study on drag and heat reduction of a novel combinational spiked blunt body and rear opposing jet concept in hypersonic flows

A novel combinational configuration is proposed for drag and heat reduction in this paper, the CFD numerical method is adopted to study its drag and heat reduction performance. The results show that the aerodisk enhances the compression of hypersonic free stream by the spike to reduce the intensity of reattachment shock wave. The rear jet pushes the reattachment shock wave away from the blunt body and reduce the intensity of reattachment shock wave as well. In addition, the low-temperature gas from rear jet can also cool the blunt body directly. Increasing the length-diameter ratio of the spike reduces the intensity of reattachment shock wave, the rear jet gas can be ejected farther to push the reattachment shock wave father away from the blunt body. Increasing the diameter of aerodisk enhances the compression of hypersonic free stream to reduce the intensity of reattachment shock wave, while the shock wave drag of spike gradually increases. Therefore, with the increase of diameter of aerodisk, the total drag coefficient of combinational configuration first decreases and then increases. The rear jet presents the long penetration mode and short penetration mode. Increasing the total pressure ratio and the size of nozzle can push the reattachment shock wave away from the blunt body and reduce the intensity of reattachment shock wave, more low-temperature gas can also be injected into the flow field to cool the blunt body effectively. Finally, the flat disk has better drag and heat reduction performance than conical disk and hemispherical disk.

Penetration mode effect on thermal protection system by opposing jet

The effect of the penetration mode on the thermal protection system by opposing jet is studied in this paper. The results show that the opposing jet not only pushes the bow shock away from the blunt body and reduces the shock intensity, but also directly cools the blunt body by the low-temperature jet gas. Therefore, the opposing jet can significantly reduce the aerodynamic heating of the blunt body. When the total pressure ratio of the opposing jet is less than critical value, the opposing jet presents the long penetration mode. When the total pressure ratio is greater than critical value, the opposing jet presents the short penetration mode. The critical total pressure ratio gradually decreases with the increase of diameter of the opposing jet. Increasing the total pressure ratio and diameter of the opposing jet can improve the thermal control efficiency of the opposing jet, and increasing diameter of the opposing jet can also reduce the drag coefficient. However, the drag coefficient increases abruptly when the penetration mode changes.

Numerical Study of the Effects of a Counterflow Jet on the Drag Reduction of a Blunt Body in a Hypersonic Flow

A numerical investigation has been conducted for the drag reduction of a counterflow jet with a blunt body at Mach 6. The computational study was carried out by solving two-dimensional axisymmetric Reynolds-averaged Navier–Stokes (RANS) equations. The Spalart–Allmaras one-equation turbulence model was used in this study. The jet flow of exit Mach number 2.86 interacts with the free stream and changes the single shock structure to a multiple shock structure. The purpose of this study was to investigate the influence of the stagnation pressure based on a parameter, the momentum parameter ratio (MPR), which can characterize the jet. The result shows that the flow field can be categorized as being in a long penetration mode (LPM) or short penetration mode (SPM) depending on the penetration length of the free-stream flow. In the LPM, under overexpanded jet conditions, the shock structure fluctuates continuously, so the flow field is unstable. On the other hand, in the SPM, the shock structure is nearly fixed, and the entire flow field is stable. For this reason, even if the penetration length of the flow field in the SPM is less than that in the LPM, the aerodynamic drag can be reduced by up to 40%. Therefore, it becomes clear that jet pressure conditions can significantly improve aerodynamic performance by reducing the drag applied to the blunt body.

Drag reduction of supersonic blunt bodies using opposing jet and nozzle geometric variations

Passive and active flow control methods are used to manipulate flow fields to reduce acoustic signature, aerodynamic drag and heating experienced by blunt bodies flying at supersonic and hypersonic speeds. This paper investigate the use of active opposing jet concept in combination with geometric variations of the opposing jet nozzle to alleviate high wave drag formation. A numerical study is conducted to observe the effects of simple jet as well as jet emanating from a divergent nozzle located at the nose of a blunt hemispherical body. An initial discussion is presented of the complex shock wave pattern flow physics occurring when opposing jet ejected from a nozzle under various operating conditions interacts with the free stream flow. The complex flow physics that include long penetration and short penetration mode is studied in conjunction with effect on drag. The numerical setup consists of supersonic free stream flow interacting with an opposing sonic jet under varying pressure ratios. Initial computational results are validated by identifying prominent flow features as well as comparing available experimental data of surface pressure distributions. Preliminary validation is followed by the introduction of a divergent nozzle in the blunt body nose region. A series of numerical iterations are performed by varying nozzle geometric parameters that include nozzle divergent angle and nozzle length for a certain jet pressure ratio. Long penetration mode, short penetration mode as well as flow separations are captured accurately during the analysis. The results show a considerable reduction in drag by the use of a divergent nozzle. Specifically, 46% and 56% reduction in drag coefficient is achieved at pressure ratio of 0.6 and 0.8 respectively in the divergent nozzle cases as compared to the simple blunt body without any nozzle.

Computational Study of Drag Reduction at Various Freestream Flows Using a Counterflow Jet from a Hemispherical Cylinder

A computational study of the counterflow drag reduction by a cold supersonic jet from a hemispherical cylinder at four different hypersonic freestream flows is conducted by solving the unsteady Reynolds-averaged Navier-Stokes (RANS) equations with the two-equation k-ɛ turbulence model. The investigations focused on two different flow regimes, SPM (short penetration mode) → LPM (long penetration mode) and LPM to ensure that the maximum drag reduction is achieved. For the present configuration, the oscillatory flow regime SPM→LPM remains dominant over the most of the pressure ratios at all the freestream flows investigated. A higher drag reduction is obtained for the higher Mach number flows at a constant pressure ratio which can be attributed to the increase in relative mass flow rate of the jet. The physical mechanism suggests that the drag reduction using a counterflow jet with different oncoming freestream flows can be expressed as a function of mass flow ratio. A relation describing the drag reduction at various freestream flows as a function of the relative mass flow rate is proposed.

Dynamics of Shock Dispersion and Interactions in Supersonic Freestreams with Counterflowing Jets

This study describes an active flow control concept that uses counterflowing jets to significantly modify external flowfields and strongly disperse the shock waves of supersonic and hypersonic vehicles to reduce aerothermal loads and wave drag. The potential aerothermal and aerodynamic benefits of the concepts were investigated by conducting experiments on a 2.6%-scale Apollo capsule model in Mach 3.48 and 4.0 freestreams in a trisonic blowdown wind tunnel, as well as pretest computational fluid dynamics analyses of the flowfields, with and without counterflowing jets. The model employed three sonic and two supersonic (with design Mach numbers of 2.44 and 2.94) jet nozzles with exit diameters ranging from 0.25 to 0.5 in. The schlieren images were consistent with the pretest computational fluid dynamics predictions, showing a long penetration mode jet interaction at low jet flow rates of 0.05 and 0.1 Ib m /s, whereas a short penetration mode jet was revealed at higher flow rates. The long penetration mode jet appeared to be almost fully expanded and was unsteady, with the bow shock becoming so dispersed that it was no longer discernible. High-speed camera schlieren data revealed the bow shock to be dispersed into striations of compression waves, which suddenly coalesced to a weaker bow shock with a larger standoff distance as the flow rate reached a critical value. Heat transfer results showed a significant reduction in heat flux, even giving negative heat flux for some short penetration mode interactions, indicating that the flow wetting the model had a cooling effect, instead of heating, which could significantly impact thermal protection system requirements and design. The findings suggest that high-speed vehicle design and performance can benefit from the application ofcounterflowing jets as an active flow control.

Influence of a Counterflow Plasma Jet on Supersonic Blunt-Body Pressures

Aerodynamic augmentation in the presence of a thin high-temperature onboard plasma jet directed upstream of a slightly blunted cone was studied experimentally and numerically. The flow around a truncated cone cylinder at zero incidence was considered for Mach numbers M∞ = 2.0, 2.5, and 4.0. For the first time, computationally validated experimental pressure distributions over the model surface in the presence of the plasma jet were obtained. As in the conventional (nonplasma) counterflow jet, two stable operational regimes of the plasma jet were found. These were a short penetration mode and a long penetration mode (LPM) aerospike into the opposing supersonic freestream. The greatest drag reduction occurred in the moderate LPM regime. LPM strong overblowing reduces the benefits. The experimental pressure results were approximately validated against an Euler computational fluid dynamics simulation, modeling a perfect gas hot jet, counterflowing against a perfect gas supersonic freestream. Plasma effects such as electron pressure, radiation, electric field interactions, Joule heating, and induced vorticity, streamers, and plasmoids have been identified that, if accounted for, may improve the comparison. Procedures for the use of these experimental results have been outlined as a baseline that will be useful in separating fluid dynamic/thermal effects from plasma processes in understanding the physics of onboard plasma jets for aerodynamic augmentation.