Straight Cone Research Articles

The influence of guide vane opening on internal cavitation of Francis turbine

Abstract In response to the theme of national multi energy complementary power grid construction, hydropower stations need to frequently change the opening of active guide vanes. Operation deviates from the rated working condition. And output is adjusted to meet the flexible power demand of users. Cavitation phenomenon as the biggest problem restricting the eccentric operation of Francis turbine. Easily induce cavitation damage to the flow passage components of the unit and shorten the service life of the unit. Therefore, there is a good engineering research background for the cavitation characteristics inside Francis turbines in the process of exploring the variation of guide vane opening. This paper takes a high head Francis turbine as the research object, based on numerical simulation and model test. The results show that the maximum amplitude of the draft tube vortex gradually increases during the process of decreasing the opening. The degree of cavitation is gradually serious, and the streamline distribution of the flow field inside the impeller is uneven. As the opening of the guide vane gradually increases, the vortexof the draft tube gradually decreases. The cavitation degree is weakened, and the streamline distribution inside the impeller is significantly improved. With the increase of the guide vane opening, the low-speed area on the outlet surface of the impeller gradually decreases, resulting in a gradual reduction of the low-speed zone in the straight cone section of the draft tube, a smaller vortex, a weaker cavitation degree. The internal flow distribution of the impeller is significantly improved.

Boundary-layer instability on a highly swept fin on a cone at Mach 6

The growth and characteristics of linear, oblique instabilities on a highly swept fin on a straight cone in Mach 6 flow are examined. Large streamwise pressure gradients cause doubly inflected cross-flow profiles and reversed flow near the wall, which necessitates using the harmonic linearized Navier–Stokes equations. The cross-flow instability is responsible for the most-amplified disturbances, however, not all disturbances show typical cross-flow characteristics. Distinct differences in perturbation structure are shown between small ( $\sim$ 3–5 mm) and large ( $\sim$ 10 mm) wavelength disturbances at the unit Reynolds number $Re' = 11 \times 10^6$ m $^{-1}$ . As a result, amplification measurements based solely on wall quantities bias a most-amplified disturbance assessment towards larger wavelengths and lower frequencies than would otherwise be determined by an off-wall total-energy approach. A spatial-amplification energy-budget analysis demonstrates (i) that wall-normal Reynolds-flux terms dictate the local growth rate, despite other terms having a locally larger magnitude and (ii) that the Reynolds-stress terms are responsible for large-wavelength disturbances propagating closer to the wall compared with small-wavelength disturbances. Additionally, the effect of free-stream unit Reynolds number and small yaw angles on the perturbation amplification and energy budget is considered. At a higher Reynolds number ( $Re' = 22 \times 10^6$ m $^{-1}$ ), the most-amplified wavelength shrinks. Perturbations do not behave self-similarly in the thinner boundary layer, and the shift in most-amplified wavelength is due to decreased dissipation relative to the lower-Reynolds-number case. Small yaw angles produce a streamwise shift in the boundary layer and disturbance amplification. The yaw results quantify a potential uncertainty source in experiments and flight.

Heat transfer characteristics of water jet impingement on high-temperature steel plate by angular nozzle

The average jet flow rate, vapor volume fraction inside the nozzle, and the distribution of pressure, shear force, turbulence intensity, temperature, and Nusselt number on the heat transfer surface were simulated when water jet impinged on a 900 °C steel plate by a straight cone nozzle and an angular nozzle under the condition of 0.7 MPa inlet pressure. Results indicate that the strong cavitation effect of the angular nozzle makes its jet impingement heat transfer intensity superior to the straight cone nozzle. Although the average jet flow rate of the angular nozzle is 3.33% lower than that of the straight cone nozzle, its shear force, turbulence intensity and Nusselt number at the stagnation point are 18.43%, 20.43%, and 18.81% higher than those of the straight cone nozzle. Experiments also show that the jet impingement heat transfer intensity of the angular nozzle is better than that of the straight cone nozzle. Its maximum cooling rate at the stagnation point increased by 13.16%, and the time to reach the maximum cooling rate decreased by 60%, compared with the straight cone nozzle. It is hoped that the results can help improve the performance of online cooling equipment for hot-rolled steel.

Structure optimization of straight cone nozzle and its effect on jet impingement heat transfer

In order to reduce the pressure loss of the nozzle and boost the efficiency of jet impingement heat transfer, this article takes the flow coefficient as the target variable and uses response surface methodology to optimize the straight cone nozzle’s internal structure. The optimal structural parameters obtained are as follows: the contraction angle is 30° and the lengths of the contraction section and the outlet section are 5 and 2 times of the outlet diameter, respectively. Besides, the influence of nozzle structural parameters on the heat transfer characteristics of a single water jet impinging on a high-temperature steel plate are simulated by ANSYS-Fluent. According to the results, the optimized nozzle has the largest flow coefficient, and the average Nusselt number on the steel plate is also the largest under the same inlet pressure.

Numerical Study of the Internal Fluid Dynamics of Draft Tube in Seawater Pumped Storage Hydropower Plant

Pumped storage hydropower plants are renewable energy systems that are effective in saving energy and solving electricity peak-on shortage. Seawater pumped storage hydropower plants are a novel type of pumped storage hydropower plant specifically supplying electric power for ocean islands with the support of solar energy and wind energy. Compared with traditional pumped storage hydropower plants that are constructed on the mainland, seawater pumped storage hydropower plants should take the influence of the complex marine environment, such as extreme waves and winds, into consideration. Taking the characteristics of waves near islands in the East China Sea as an example, we explored the transient hydraulic characteristics in the draft tube of a pump turbine under wave disturbance using a sliding grid interface and the detached eddy simulation (DES) turbulence model. By analyzing the characteristics of unsteady flow in the draft tube, the vortex characteristics under the Q criterion, the frequency characteristics of the pressure pulsation, the evolution law of the internal fluid, and the propagation law of the pressure pulsation were explored. For the situation without wave disturbance, an obvious eccentric vortex in the straight cone section of the draft tube was observed in the case where the opening of the guide vane was small. With the increase in the opening of the guide vane, the eccentric vortex gradually dissipated. For the situation with wave disturbance, the main frequency of the draft tube equaled the frequency of the wave disturbance, the maximum pressure pulsation at the selected monitoring points increased 5 to 15 times, and the superposition of the wave pressure pulsation signals and the draft tube pressure pulsation produced more low-frequency, high-amplitude pressure pulsation signals. Even though the pressure pulsation frequency spectrum varied a lot, the frequency domain of the pressure pulsation without wave disturbance still existed. In addition, the wave disturbance merely varied with the pressure of the draft tube. The influence of wave disturbance on the pressure distribution in the draft tube was relatively small. The results can provide a reference for the operation of seawater pumped storage hydropower plants.

Performance analysis of cyclone separators with bulged conical segment using large-eddy simulation

The present study proposes and investigates the performance of novel cyclone separators with bulged conical sections. For this, the curved profile replaces the straight cone wall while using the two fixed ends of the former – the resulting cyclone model resembles the shape of a pot. Five different cyclone configurations with a curvature radius equal to 1.5, 1.25, 1.0, 0.75, and 0.5 m are considered. Advanced closure large-eddy simulation (LES) has been used for numerical simulations to evaluate the mean and fluctuating flow field, collection efficiency, and pressure losses. Conclusive results indicate that the pressure drop and the collection efficiency decrease with an increasing curvature size. Since the proposed model has a larger separation space to accumulate more solid particles than the conventional design, it can be potentially utilized as the pre-separators.

AXOIDS OF HOOKE’S JOINT

The analysis of literary sources devoted to the research and construction of cardan transmissions using the Hooke's joint showed that the peculiarities of the spherical movement of the cardan joint crosspiece are insufficiently covered. This is explained by the relatively small weight of the crosspiece, due to which it almost does not affect the dynamics of the cardan transmission. The need to take into account the mass-geometric parameters of the crosspiece and to analyze comprehensively its movement may arise during accurate calculations of high-speed cardan transmissions. In this case, it is convenient to consider the movement of the crosspiece as rolling without sliding of the moving axoid on the stationary axoid. This approach makes it possible to more fully investigate the peculiarities of the spherical movement of the crosspiece and gives a visual representation of the orientation of its instantaneous axis of rotation in fixed and moving coordinate systems. Based on this, this work is devoted to the construction of a kinematic model of the Hooke's joint crosspiece, the movement of which is considered as rolling without sliding of a moving axoid on a stationary one.
 As a result of the kinematic analysis of the Hooke's joint, the equations of the hodographs of the vector of the absolute angular velocity of the crosspiece in the fixed and moving coordinate systems were obtained, and the parameters of the fixed and moving axoids of the crosspiece of the cardan joint were determined. It is proved that the stationary axoid of the crosspiece of the Hooke's joint is an oblique elliptic cone with the apex in the center of the crosspiece, and its opposite generatrices, crossing the major axis of the guide ellipse, coincide with the axes of the drive and driven shafts of the joint. The moving axoid of the crosspiece is a closed conical surface with a variable opening angle, the maximum value of which is equal to twice the value of the interaxial transmission angle. With small values of the interaxial angle, which occur in the practice of using a single Hooke’s joint, a moving axoid can be approximately considered as a straight circular cone with a vertex in the center of the crosspiece and an opening angle equal to twice the value of the interaxial transmission angle. The error of this assumption increases rapidly with the increase of the interaxial transmission angle. The correctness of the obtained mathematical model was confirmed by computer modeling in the Autodesk Inventor environment.
 The obtained results can be used in the study of dynamic processes that occur in cardan transmissions using Hooke's joint.

Accurately predicting hypersonic transitional flow on cone via a symmetry approach

A new algebraic transition model is proposed based on a Structural Ensemble Dynamics (SED) theory of wall turbulence, for accurately predicting the hypersonic flow heat transfer on cone. The model defines the eddy viscosity in terms of a two-dimensional multi-regime distribution of a Stress Length (SL) function, and hence is named as SED-SL. This paper presents clear evidence of precise predictions of transition onset location and peak heat flux of a wide range of hypersonic Transitional Boundary Layers (TrBL) around straight cone at zero incidence, to an unprecedented accuracy as validated by over 70 measurements for varying five crucial influential factors (Mach number, temperature ratio, cone half angle, nose Reynolds number and noise level). The results demonstrate the universality of the postulated multi-regime similarity structure, in characterizing not only the spatial non-uniform distribution of the eddy viscosity in hypersonic TrBL on cone, but also the dependence of the transition onset location on the five influential factors. The latter yields a novel correlation formula for transition center Reynolds number which takes similar functional form as the SL function within the symmetry approach. It is concluded that the SED-SL model simulates TrBL around cone with uniformly high accuracy, and then points out to an optimistic alternative way to construct hypersonic transition model.

Roughness effect on hypersonic second mode instability and transition on a cone

Recent studies by Fong et al. [“Finite roughness effect on modal growth of a hypersonic boundary layer,” AIAA Paper No. 2012-1086, 2012; “Stabilization of hypersonic boundary layer waves using 2-D surface roughness,” AIAA Paper No. 2013-2985, 2013; “Numerical simulation of roughness effect on the stability of a hypersonic boundary layer,” Comput. Fluids 96, 350–367 (2014); and “Second mode suppression in hypersonic boundary layer by roughness: Design and experiments,” AIAA J. 53, 1–6 (2015)] have shown that finite roughness can attenuate Mack's second mode instability when placed at the discrete mode synchronization location for two-dimensional planar flow over a flat plate. However, more practical hypersonic flows are non-planer conical flows, and the roughness effect phenomenon in conical flows has not been extensively investigated. For that reason, this investigation research the ability of finite roughness strips to attenuate the second mode instability on a Mach 8 straight blunt cone with a freestream unit Reynolds number of 9 585 000. Two roughness configurations are studied: a single roughness strip and an array of six sequential strips. N-factor calculations determine the second mode frequency most likely to lead to turbulent transition, and the linear stability theory is used to determine the mode's synchronization location. In the unsteady simulations of the roughness configurations, a blowing-suction actuator introduces an upstream broadband Gaussian pulse. Fourier decomposition of the pulse's history shows that the single roughness strip attenuates frequencies higher than 208 kHz while lower frequencies are amplified. Likewise, the roughness array exhibits similar results, attenuating frequencies higher than 164 kHz and amplifying lower frequencies downstream. The results show that both configurations can delay second mode instability growth on a hypersonic blunt cone and possibly delay turbulent transition. However, investigations of the roughness effect's behavior downstream of the roughness configurations show that disturbance growth resumes and becomes more destabilizing to the boundary layer.

Calculation method and model tests of pile frost jacking for railway overhead contact systems in permafrost regions

One of the major challenges encountered in electrification reconstruction project of Golmud-Lhasa section of Qinghai-Tibet railway of China is ensuring the frost jacking stability of the pile foundation of overhead contact system mast (OCSM). To evaluate the resisting frost jacking performance of OCSM pile in permafrost regions, a theoretical model of OCSM pile in permafrost soils under the effect of frost heave was constructed based on superposition principle and deformation coordination relationship between the pile and soil. The model was solved by using the finite difference method combined with MATLAB. Then, large scale model tests were performed to investigate the thermodynamic behaviors of OCSM piles with different sections (equal section circular pile, straight cone cylindrical pile and curved cone cylindrical pile) in the permafrost soils under freeze-thaw actions, after which the theoretical model were validated. It was found that distribution curves of pile axial force obtained by the calculation method is basically consistent with model test results in the overall trend, implying that the calculation model is reasonable and feasible. During soil freezing, the pile is under tension as a whole, and the axial force is greatest near the depth of frost penetration. The maximum value of tangential frost-heave stress occurs near the ground surface. The total tangential frost heaving force of the curved cone cylindrical pile is the smallest, and the effect of resisting frost jacking is the best. These research results can provide a reference for resisting frost jacking design of OCSM pile in permafrost regions.

Experimental Investigation of Hypersonic Boundary Layer Transition on a 5° Smooth Straight Cone

Experimental Investigation of Hypersonic Boundary Layer Transition on a 5° Smooth Straight Cone

Experimental study of the separation performance of a hydrocyclone with a compound curve cone

The entrainment of fine particles in the underflow and coarse particles in the overflow is a well-known problem in separation using a conventional cylindrical–conical hydrocyclone that reduces the separation accuracy and efficiency. To address this problem, this paper presents a hydrocyclone equipped with a compound curved cone (the CCC hydrocyclone). The CCC hydrocyclone was experimentally compared with a hydrocyclone with a conventional straight cone (the CSC hydrocyclone) in terms of five separation performance metrics, namely, the split ratio, total separation efficiency, concentration and particle size of the products, and grade efficiency. To provide further guidance on the application of the CCC hydrocyclone in real-world production, the effects of three process parameters—the underflow apex diameter and the particle mass concentration and pressure of the feed—on the separation performance of the CCC hydrocyclone were investigated in depth. Moreover, the CCC hydrocyclone was successfully used in a real-world industrial application.

Optimization Design and Analysis of Bionic Friction Reducing Nozzle in Oil Shale High-Pressure Jet Mining

The borehole hydraulic mining method has unique advantages for underground oil shale exploitation. Breaking rock with a high-pressure water jet is a crucial step to ensure the smooth implementation of borehole hydraulic mining in oil shale. The hydraulic performance of the nozzle determines the efficiency and quality of high-pressure water jet technology. To obtain a superior hydraulic performance nozzle, based on the bionic non-smooth theory, a circular groove was selected as the bionic unit to design a bionic straight cone nozzle. The structural parameters of the circular groove include the groove depth, width, and slot pitch. The optimization objective was to minimize the pressure drop, where the fluid has the least resistance. A genetic algorithm was used to optimize the structural parameters of the circular grooves in the inlet and outlet sections of the bionic straight cone nozzle. The optimal structural parameters of the nozzle were as follows: the inlet diameter was 15 mm, the inlet length was 20 mm, the outlet diameter was 4 mm, the length-to-diameter ratio was 3, and the contraction angle was 30°. In addition, in the inlet section, the groove width, slot pitch, and groove depth were 3.9 mm, 5.2 mm, and 5.5 mm, respectively, and the number of circular grooves was 2. Moreover, in the outlet section, the groove width, slot pitch, and groove depth were 2.25 mm, 3 mm, and 5.5 mm, respectively, and the number of circular grooves was 2. The CFD numerical simulation results showed that under the same numerical simulation conditions, compared with the conventional straight cone nozzle, the bionic straight cone nozzle velocity increase rate could reach 13.45%. The research results can provide scientific and valuable references for borehole hydraulic mining of high-pressure water jets in oil shale drilling.

Heat Flux on a Hypersonic Cone with a Highly Swept Fin

A detailed comparison between computations and experiments is given for Mach 6 flow over a straight cone with a highly swept fin. Five cases are simulated that vary the cone nose radius, fin thickness, fin sweep angle, and freestream unit Reynolds number. Experimental data are available for four cases. Surface heat flux comparisons between steady, laminar simulations and experimental measurements are made on the surface of the cone and fin. Uncertainty for both computations and experiments is estimated. Three cases are identified as transitional or turbulent, while one case is identified as laminar. Estimates of transition location are derived from experimental heat transfer and measurements of surface pressure fluctuations over a range of unit Reynolds numbers. The effect of geometric parameters is deduced. Further investigation into geometric changes demonstrates the sensitivity of the finned cone flowfield (e.g., vortex location and strength) to the shape of the fin–cone junction. Additionally, simulations demonstrate that the flow on the fin and cone is largely unaffected by truncating the fin. Changes in the flowfield remain localized to the fin truncation.

A symmetry-based length model for characterizing the hypersonic boundary layer transition on a slender cone at moderate incidence

The hypersonic boundary layer (HBL) transition on a slender cone at moderate incidence is studied via a symmetry-based length model: the SED-SL model. The SED-SL specifies an analytic stress length function (which defines the eddy viscosity) describing a physically sound two-dimensional multi-regime structure of transitional boundary layer. Previous studies showed accurate predictions, especially on the drag coefficient, by the SED-SL for airfoil flows at different subsonic Mach numbers, Reynolds numbers and angles of attack. Here, the SED-SL is extended to compute the hypersonic heat transfer on a 7 ∘ half-angle straight cone at Mach numbers 6 and 7 and angles of attack from 0 ∘ to 6 ∘. It is shown that a proper setting of the multi-regime structure with three parameters (i.e. a transition center, an after-transition near-wall eddy length, and a transition width quantifying transition overshoot) yields an accurate description of the surface heat fluxes measured in wind tunnels. Uniformly good agreements between simulations and measurements are obtained from windward to leeward side of the cone, implying the validity of the multi-regime description of the transition independent of instability mechanisms. It is concluded that a unified description for the HBL transition of cone is found, and might offer a basis for developing a new transition model that is simultaneously of computational simplicity, sound physics and greater accuracy.

Investigation of Flow Characteristics of Flow Passage Components in Francis Turbine under No-load and 50% Load operating conditions

Due to the varying demand of power grid for the electric supply of hydraulic power stations, the units are often under low-load operating condition and no-load standby state, causing a significant flow instability in hydraulic generator units. To further investigate the inside flow characteristics of hydraulic turbines under such operating conditions. In this study, a CFD (computational fluid dynamics) numerical simulation with applying RNG (Renorm alization Group) k-ε turbulence model is performed to study the inside flow characteristics of each flow passage components of a Francis turbine under no-load and 50% load conditions. The results indicate that under the two operating conditions, the flow distribution inside and outside the draft tube pier is significantly nonuniform. Simultaneously, the large-scale vortex in the runner area caused by the high-speed flow in the vane-free area with small opening and the nonuniform flow velocity distribution in the straight cone section of the draft tube are the main reasons for the increase of hydraulic loss and the decrease of efficiency.

The physiology of polar bear mating (Ursus maritimus)

The well‐being of any species depends on successful reproduction, so the study of mating is essential, mainly to prevent the extinction of rare animals. In the process of evolution, each new species has adapted to environmental conditions in the struggle for survival through the morphological and physiological characteristics of the reproductive anatomy. Polar bear mating lasts 10‐20 minutes and corresponds to uterine insemination, but the description of the physiology of polar bear mating is lacking due to technical difficulties. Studies of the penis of a polar bear during an erection caused by the impact of electrical impulses of an electro‐ejaculator on the pudendal and external spermatic nerves and smooth muscles of the genital organs before reaching ejaculation to obtain sperm suggest how this happens. We studied the manifestation of sexual reflexes in a male polar bear (Ursus maritimus), age 10 years. The bear was kept in the Kazan Zoo from birth and did not participate in mating. An electro‐ejaculator was used to collect sperm. We have established the following features: the penis was covered entirely with a prepuce (praeputium) in a not erect state. The length of the penis is 19 cm. It practically does not change due to the presence of the os penis, which is 18.6 cm long and extends into the head of the penis. The diameter of the body of the penis is 1.5 cm. Initially, the head was 2 cm in diameter, two plates stood out on it, filling with blood during an erection. The opening of the urogenital canal (canalis urogenitalis) extends with its free end outside the head and has soft processes at the end of the canal. The length of the processes of the free end of the canal is 6 mm, and the width of their bifurcation is 4 mm. During an erection, the shape and size of the body of the penis (corpus spondiosum glandis) change and increase. The spongy body of the glans penis swells like a conus from the main shaft with the broadest part at the end. It has a length of 4 cm. The upper part is like an ellipse inclined at an angle of 45 degrees to the plane of the cone. Further, the head of the penis (glans penis) increases and takes the form of a straight cone with swollen urogenital canal sponges about 20 mm long, 10 mm in diameter at the base, 15 mm at the end. In the upper part, the funnel has an outer diameter of 40 mm, takes an angle of almost 90 degrees to the shaft of the penis, looks like a hand pump cuff. It can be assumed that the function of the swollen sponges is to ensure maximum passage of seminal fluid through the cervix, which is 15 mm long and opens during mating, and to prevent sperm leakage during insemination. They close the backflow of seminal fluid from the body of the uterus. During intercourse, the ejaculate pours into the vagina and partly irrigates the cervix. During coitus, it occurs from 3 involuntary muscle contractions of the body, which indicate stepped ejaculation (in portions). However, polar bears should be regarded as animals with uterine type of insemination, the highly swelling glans of the male penis, poorly covered by the walls of the vagina, acts on the principle of a piston. The penis pushes ejaculate from the vagina into the uterus.

A nonlinear compressible flow disturbance formulation for adaptive mesh refinement wavepacket tracking in hypersonic boundary-layer flows

A new numerical approach for simulating nonlinear wavepackets in hypersonic boundary-layers is presented. The adaptive mesh refinement wavepacket tracking (AMR-WPT) method has been developed as an efficient alternative to conventional direct numerical simulations (DNS). The AMR-WPT method employs the nonlinear disturbances equations (NLDE), an overset dual mesh approach with higher-order interpolation, and adaptive mesh refinement (AMR) to track wavepackets in hypersonic boundary-layer flows. After introducing the numerical details, the method is used to simulate linear and nonlinear wavepackets for an axisymmetric M=9.81 straight cone and 2-D/3-D M=5.35 flat plate boundary-layer. The simulation results are compared against classical stability and transition prediction tools, such as linear stability theory (LST), parabolized stability equations (PSE) and DNS. It is demonstrated that the AMR-WPT method requires only about 10% of the number of grid points when compared to DNS of a nonlinear wavepacket inside a hypersonic flat plate boundary-layer flow.

An improved physics-informed transition-turbulence model for asymmetric transition over supersonic rotating projectiles

On the surface of a rotating projectile flying with a supersonic speed, due to the rotational motion, an asymmetric boundary layer transition will occur. This boundary layer distortion caused by the rotation has a significant contribution to the Magnus effect, which will produce a large instability moment and cause flight instability. Therefore, it is of great significance to conduct in-depth research and flow mechanism analysis on the asymmetric boundary layer transition phenomenon on the surface of high-speed rotating projectiles. On the one hand, in supersonic boundary layers, the steamwise flow instability modes are mainly the first mode and the laminar flow separation mode; on the other hand, strong crossflow velocity shear will be generated in the self-rotating state of the projectile and the compressible crossflow instability plays an extremely important role. This paper proposes a physics-informed transition-turbulence model suitable for supersonic/hypersonic boundary layers, which contains physical instability mechanisms and all variables can be solved locally. New time scales for the first mode and crossflow mode are developed. Furthermore, compressibility corrections and cooled wall modifications are performed on the model. Based on this model, we conducted the unsteady simulations of the high-speed rotating straight cone, and carefully compared the mesh sensitivity. In detail, the boundary layer transition characteristics under different Mach numbers, angles of attack, Reynolds numbers and rotational speeds are analyzed through the present transition-turbulence model. Decent agreement with the experiment data verifies that the transition-turbulence model developed by the authors can be applied to predict the asymmetric transition phenomenon on the supersonic flying rotating projectiles with high accuracy.

Hypersonic boundary layer transitions over a yawed, blunt cone

The boundary layer transition process for a straight circular cone with angle of attack (AoA) of 6° at Mach 6 was studied via high-resolution direct numerical simulations and stability analyses. A pair of strong streamwise vortices simultaneously induced a low-speed mushroom structure to emerge near the leeward plane. This structure was subject to low-frequency sinuous and high-frequency varicose instabilities. The transition between windward and leeward rays likely occurred due to the interactions between low-frequency traveling and stationary crossflow vortices. The lower-amplitude high-frequency secondary crossflow instability mode could be traced back to the upstream Mack mode. Although the axial and crossflow vortices were fundamentally different, there was a striking similarity between them since both high-frequency perturbations were driven by azimuthal shear and resulted in staggered positive and negative axial vortices along the streamwise direction.