Reattachment Zone Research Articles

Superposition and Amplitude Modulation Effects in Separated Flow

Abstract This article adopts direct numerical simulation method to study concave cavity flow with high Reynolds number, and explores the influence of outer region structure on inner region turbulence of concave cavity flow, as well as the mechanism of coherent structure in the near wall region of concave cavity flow. This article finds that the superposition and amplitude modulation effects of separated flow are weaker than those in smooth wall turbulence. At different positions within the concave cavity, the superposition effect in the reattachment zone is the strongest, while the superposition effect in the separation zone is the weakest, indicating that flow separation prevents large-scale structures from outer region penetrating into the near wall region. The amplitude modulation effect of the reattachment point is the strongest, which is related to the strong adverse pressure gradient of the reattachment point.

New insights on cavitating flows over a microscale backward-facing step

This study introduces the first experimental analysis of shear cavitation in a microscale backward-facing step (BFS) configuration. It explores shear layer cavitation under various flow conditions in a microfluidic device with a depth of 60 μm and a step height of 400 μm. The BFS configuration, with its unique characteristics of upstream turbulence and post-reattachment pressure recovery, provides a controlled environment for studying shear-induced cavitation without the complexities of other microfluidic geometries. Experiments were conducted across four flow patterns: inception, developing, shedding, and intense shedding, by varying upstream pressure and the Reynolds number. The study highlights key differences between microscale and macroscale shear cavitation, such as the dominant role of surface forces on nuclei distribution, vapor formation, and distinct timescales for phenomena like shedding and shockwave propagation. It is hypothesized that vortex strength in the shear layer plays a significant role in cavity shedding during upstream shockwave propagation. Results indicate that increased pressure notably elevates the mean thickness, length, and intensity within the shear layer. Instantaneous data analysis identified two vortex modes (shedding and wake modes) at the reattachment zone, which significantly affect cavitation shedding frequency and downstream penetration. The wake mode, characterized by stronger and lower-frequency vortices, transports cavities deeper into the channel compared to the shedding mode. Additionally, vortex strength, proportional to the Reynolds number, affects condensation caused by shockwaves. The study confirms that nuclei concentration peaks in the latter half of the shear layer during cavitation inception, aligning with the peak void fraction region.

Flow past two diamond-section cylinders in tandem arrangement at a low Reynolds number

The unsteady flow surrounding two fixed diamond cylinders is analyzed at Reynolds number 100 over normalized center-to-center spacing ratios 2−15. By analyzing the contours of instantaneous vorticity, variations of recirculation length, surface pressure, and fluid forcing of cylinders, the value of normalized critical spacing is found to be 3.4. In the reattachment zone below critical spacing, vortex-shedding from the upstream (UC) and downstream (DC) cylinders is anti-phase. At the critical spacing, regular vortex-shedding commences also from the UC, and vortex-shedding from the cylinders becomes phase synchronized for the first time. The analysis of a vortex-shedding cycle at the critical spacing reveals that the cylinders shed vortices at the same frequency, but with a time delay. Impingement of vortices shed from the UC on the DC strengthens vorticity around the DC and shifts the instantaneous position of its forward stagnation point from the leading edge. The understanding that locations of stagnation points govern the direction and magnitude of lift force comes from the analysis of flow at the critical gap. When the surface bounded by stagnation points is occupied mostly with negative vorticity, the instantaneous lift is negative and vice versa. At critical spacing, mean streamlines show the emergence of an anti-wake at forward stagnation point of the DC for the first time. Over the entire range of cylinder separation, nine distinct patterns of separation topologies are identified. Below critical spacing, both pressure and viscous drag components, and hence, total drag of the DC are negative or upstream-acting.

Experimental study on the heat flux of transitional shock wave–boundary layer interaction at Mach 6

The shock wave–boundary layer interaction (SWBLI) phenomenon was investigated experimentally to explore the heat flux distribution characteristics of SWBLIs under different boundary layer flow regimes and the influence/mechanism of different transition positions on peak heat flux of SWBLI. Experiments were conducted in a flow of Mach number 6. The shock generator deflected the flow by 20 °, 22 °, 25 ° and 30 ° resulting in an oblique shock impinging on a flat plate. The rough elements with different heights were arranged to achieve different transition positions. The influence of the relative position of transition and interference zone on the peak heat flux and its physical mechanism are revealed. The results demonstrated that the transitional SWBLI has a higher peak heat flux than the turbulent SWBLI, however the overshoot phenomenon is not reflected in the peak pressure. The increment of heat flux peak in transitional SWBLI is related to the relative positions of transition and interference zones. The increment of heat flux peak of transitional SWBLI compared to turbulent SWBLI can reach 25.5–38.9% and 51.9–65.1% when transition approaches the separation zone and reattachment zone, respectively. This overshoot phenomenon is caused by the streamwise vortex in transitional and so-called laminar SWBLIs, which enhances the energy exchange in the boundary layer and leads to an increase in heat flux. However, in the turbulent SWBLI, the energy mixing in the boundary layer is not significantly enhanced due to the breakup of the large scale streamwise vortex into turbulent small-scale structure.

Generalisation of the Penalised Wall Function Method for the Simulation of Turbulent flows With Unfavourable Pressure Gradients

The penalized wall function method for simulation of compressible near-wall turbulent flow regions in the numerical modeling of viscous compressible flows is developed. The method is formulated as a differential condition to match the outer and the wall function solutions and is based on a generalized characteristic-based volume penalization method to transfer shear stress from the outer region of the boundary layer to the wall. The method is modified to extend its applicability to turbulent flows with adverse pressure gradient, when separation and reattachment zones are formed, as well as to use computational meshes with coarser near-wall resolution. These advantages are demonstrated for two test problems, namely, the flow over a flat plate with zero and adverse pressure gradients.

Evolution of unsteady secondary flow structures near the onset of stall in a tip-critical transonic axial flow compressor stage

The aerodynamic stability of an axial compressor stage depends on the rotor and stator. However, due to the specific design requirements, the evolving flow field and the resulting secondary flow structures are different in both components. This study investigates the evolution of dominant secondary flow structures occurring in the rotor and stator of a tip-critical transonic compressor stage at the near-stall condition using unsteady numerical analysis and validates performance characteristics with the experimental data. The investigation reveals that the presence of rotor tip shock creates a large difference in the pressure gradient across the pressure surface and the suction surface, intensifying tip leakage flow and shock-induced boundary layer separation. The higher incidence angle near the hub leading edge creates a local separation and reattachment zone. The radial pressure gradient causes the low momentum flow from this local separation zone to migrate radially upward. This migrated flow interacts with the tip leakage flow and separated blade boundary layer, eventually creating a colossal recirculation zone and subsequent rotor blockage of around 46%. The increasing streamwise adverse pressure gradient pushes the tip shock upstream, and at the onset of the stall, the flow directly separates from the rotor leading edge avoiding the shock formation. The stator flow field is dominated by the asymmetric hub corner separation induced by the streamwise adverse pressure gradient and the tip corner separation caused by the vortex structures convected downstream from the rotor tip region leading to stator blockage of around 48%. Along with the blade passing frequency, four other dominating frequencies (0.06×BPF, 0.12×BPF, 0.44×BPF, and 0.84×BPF) related to the aerodynamic instabilities are observed at the inception of stall.

Simulation of High-Enthalpy Turbulent Shock Wave/Boundary Layer Interaction Using a RANS Approach

In the era of space exploration, the scientific community is strongly focusing on the analysis of hypersonic flows in the presence of shock wave/boundary layer interaction. In these conditions, the flow field presents a complex shock structure due to the interaction of different shock waves with the boundary layer. The strong adverse pressure gradient makes the boundary layer separate, giving rise to a separation bubble. In the reattachment zone, the temperature can reach very high values, inducing thermochemical non-equilibrium effects. This research field is recently achieving more and more relevance in aerospace research, as the analysis of turbulent shock wave/boundary layer interaction so far has been mainly focused on perfect gas flows. In this manuscript, a Reynolds averaged Navier–Stokes (RANS) approach is considered, the shear stress transport (SST) model being coupled with the multitemperature approach proposed by Park to investigate thermochemical non-equilibrium effects in hypersonic turbulent shock wave/boundary layer interaction. The first part of the manuscript is devoted to the validation of the solver, and results for low enthalpy flat plate and compression ramp flows are presented. The numerical results are shown to be in good agreement with numerical solutions and experimental measurements. Afterward, the free stream conditions are modulated to make non-equilibrium relevant and analyze a reacting flow.

Direct numerical simulation of thermal turbulence in an aero-engine blade channel

The flow and heat-transfer phenomena are simulated by direct numerical simulation in the NACA65 blade channel with a Reynolds number equaling to 1.367×105. Induced by the strong adverse pressure gradient, the flow separations are observed on the suction surface with the multi-scale and multi-layer vortices. The DNS results indicates that the backflow transition is triggered by the small-scale spanwise-vortex fluctuations due to the viscous linear instability, and thereafter is further stretched into the quasi-streamwise vortices due to the upper K-H rolls, which generates the typical coherent structures in the flow-separation region. The Reynolds shear stresses and turbulent heat flux are found very strongly and actively concentrating in the region bounded by the blade-wall and the upper boundary of separation where the variety of ejections and sweeps are observed. These ejections and sweeps promote the momentum and heat transfers, which results in the large temperature gradients in both the near-wall and flow-separation regions. Moreover, the separation and reattachment zones present the non-similarity distributions for both the wall-normal heat flux and Reynold shear stresses due to the strong adverse pressure gradient. Therefore, the diverse profiles of velocity and temperature can be found developing in streamwise along the suction surface. However, through applying the newly-developed wall-bounded law formulations, it is demonstrated that these wall-laws are even universally capable of accurately representing these diverse velocity and temperature profiles.

Deposition characteristics of particles in backward-facing step flow and a radiant syngas cooler

Investigation of the mechanism of particle transport and deposition in backward-facing step (BFS) flow is conducive to enhancing the understanding of the deposition characteristics of fly ash in the radiant syngas cooler (RSC). In this study, the regional characteristics of particle deposition in BFS and RSC are deeply studied by numerical simulation. The results show that the deposition of small particles in the recirculation (RC) zone and most particles in the reattachment and redevelopment (RR) zone is promoted while that of large particles in the RC zone is inhibited by the main flow. The variation curves of dimensionless deposition velocity gradually approach to that in straight channel with the increase in deposition length, but they are little affected by the step height and inlet velocity. The differences in particle deposition rates and size distributions between the two zones in RSC are analyzed. The average deposition rate in the RC zone is 21% lower than that in the RR zone, and the proportion of particles smaller than 45.03 μm in the RC zone is higher than that in the RR zone by 24%. This study can provide a basis for the establishment of ash deposition control strategies.

Numerical Analysis of Turbulent Flow over a Backward-facing Step in an Open Channel

Abstract Computational examinations of the flow field in an open channel having a single Backward--Facing Step (BFS) with a constant water depth of 1.5 m were performed. The e ects of the expansion ratio, and the flow velocity along the reattachment length, were investigated by employing two di erent expansion ratios of 1.5 and 2, and eight various flow velocities of 0.5, 1, 2, 3, 4, 5, 7.5 and 10 m/sec in the Computational Fluid Dynamic (CFD) simulations. Commercially available CFD software, ANSYS FLUENT, was used for calculations. The simulation outcomes were verified using experimental results. Moreover, analyses were performed by using two equation turbulence closure models, K-ɛ family (standard, RNG and realizable), and K-ω family (Wilcox’s and SST K-ω). The analyses have revealed that the reattachment length increases with an increase in the expansion ratio, the flow velocity and the Reynolds number. The results obtained for two expansion rates and eight di erent flow velocities have shown insignificant di erences between one turbulence closure model and the others. Furthermore, it was observed that both velocity and expansion ratios have an e ect on the reattachment zone size.

Wall‐resolved large eddy simulation of turbulent flows in helically ribbed steam cracker reactors

AbstractHelically ribbed coils are commonly applied in steam cracking furnaces. To fully understand the impact of these ribbed wall modifications on the local heat transfer and associated pressure drop throughout the reactor, detailed experimental, and numerical studies have been performed. Experimental data based on stereo‐particle image velocimetry (S‐PIV) and liquid crystal thermography have been used to validate the numerical results from wall‐resolved large eddy simulations using OpenFOAM. The validation shows an excellent agreement in terms of mean and fluctuating velocities, pressure drop, and heat transfer behavior in a discontinuously ribbed tube. Compared with the pressure drop in a continuously ribbed tube, an approximately 40% lower pressure drop is obtained with a discontinuously ribbed tube, at the cost of a slightly decreased heat transfer enhancement. This makes the discontinuously ribbed tube design particularly interesting for steam cracking applications. The results also show that the nonuniform heat transfer at the wall is inherently linked to the flow reattachment and recirculation zones caused by the rib. Finally, the validated numerical model was used to study comparable designs and propose novel helical rib designs. Based on the results of the study, enlarging the trailing edge of the conventional ribbed geometry will improve the thermal enhancement performance, and is therefore found most promising for steam cracking reactor design.

Structure of turbulence in the flow around a rectangular cylinder

The separating and reattaching turbulent flow past a rectangular cylinder is studied to describe how small and large scales contribute to the sustaining mechanism of the velocity fluctuations. The work is based on the anisotropic generalised Kolmogorov equations, exact budget equations for the second-order structure function tensor in the space of scales and in the physical space. Scale-space energy fluxes show that forward and reverse energy transfers occur simultaneously in the flow, with interesting modelling implications. Over the longitudinal cylinder side, the Kelvin–Helmholtz instability of the leading edge shear layer generates large spanwise rolls, which get stretched into hairpin-like vortices and eventually break down into smaller streamwise vortices. Independent sources of velocity fluctuations act at different scales. The flow dynamics is dominated by pressure–strain: the flow impingement on the cylinder surface in the reattachment zone produces spanwise velocity fluctuations very close to the wall, and at larger wall distances reorients them to feed streamwise-aligned vortices. In the near wake, large von Kármán-like vortices are shed from the trailing edge and coexist with smaller turbulent structures, each with its own independent production mechanism. At the trailing edge, the sudden disappearance of the wall changes the structure of turbulence: streamwise vortices vanish progressively, while spanwise structures close to the wall are suddenly turned into vertical fluctuations by the pressure–strain.

Active control of flow over a backward-facing step at high Reynolds numbers

This work provides new insight into the transient flow effects of forcing a backward-facing step flow at high Reynolds number. The detailed flow structure and surface pressure is investigated over the range 118,000⩽ReH⩽472,000 using time-resolved particle-image velocimetry. Notably, this research considerably extends the Reynolds number ranges of previous studies. The effect of periodic shear-layer forcing on the global mean and fluctuating flow structure is examined over the forcing frequency range 0.036⩽StH⩽1.98. The effect of forcing on the base pressure, which has received relatively little attention, is also detailed. These studies allow us to characterise the relationship between the forcing frequencies, with a particular focus on frequencies near and significantly above the shear-layer instability. Importantly, despite the high Reynolds number, we are able to perturb the shear layer to control both the reattachment length and base pressure. Forcing at frequencies close to the shear-layer instability results in a significant reattachment length reduction, as has been well reported, with a corresponding base pressure reduction of up to 45%. At the highest forcing frequency, an increase in mean base pressure of 9.7% is found, with a corresponding increase in reattachment length of 3.9% over the unforced case. This high-frequency forcing reduced initial growth of the shear-layer instability and stabilised the latter half of the reattachment zone. This enabled more flow entrainment upstream to the step-base, resulting in a mean base-pressure increase. Although, this came at the cost of triple the base-pressure fluctuations, an important insight for practical flow-control applications. The spatial distribution of spectral power for key instabilities in the flow, and the influence of forcing on these distributions, is also examined. To our knowledge, the spatial distribution of these key instabilities, with or without control, has not been previously presented for high Reynolds numbers (ReH>104).

An Eddy‐Resolving Numerical Model to Study Turbulent Flow, Sediment, and Bed Evolution Using Detached Eddy Simulation in a Lateral Separation Zone at the Field‐Scale

AbstractTurbulence‐resolving simulations elucidate key elements of fluid dynamics and sediment transport in fluvial environments. This research presents a feasible strategy for applying state‐of‐the‐art computational fluid mechanics to the study of sediment transport and morphodynamic processes in lateral separation zones, which are common features in canyon rivers where massive lateral flow separation causes large‐scale turbulence that controls sediment erosion and deposition. An eddy‐resolving model was developed and tested at the field‐scale, coupling a viscous flow and sediment transport solver using Detached Eddy Simulation techniques. A morphodynamic model was applied to the viscous flow/sediment solver to calculate erosion and deposition. A simulation of turbulence was performed at the grid resolution for a straight channel to determine the relative contributions of modeled and resolved diffusivity. The time‐dependent, energetically important, correlative, non‐stationary signals of the simulated quantities were captured at the lateral separation zone. Strong periodic signals featured by high amplitude were found at the separation zone, while low frequency pulsations were observed at the reattachment zone of the lateral separation zone. Interactions between the eddies and the loose bed boundaries resulted in erosion of sediment at the main channel followed by deposition at the primary eddy and eddy bars.

Impact of Mach number on the flow pattern in suddenly expanded duct

A study is undertaken to assess the dynamic control's effectiveness at two supersonic Mach numbers, 2.2 and 2.58 being considerably large Mach number being very significant in the design of High-speed aerospace vehicles. The relief available to the flow while the shear layer exits from the nozzle and enters the enlarged duct. The investigation area ratio is 4.84, and the NPR tested is from 3 to 11, covering the various level of expansion. The investigation was done for eight sizes of circular duct cases. Still, the results are discussed only when a significant change in the wall pressure is noticed during the experimentation. The dynamic control is located at a 6.5 mm radial distance from the primary jet's axis, with a 1 mm diameter generating at sonic Mach from the active flow control management. For lower duct length at NPRs, the wall pressure assumes large values. Later, with a rise in the duct section and NPR, a progressive decline in the pressure values is seen due to the decrease in adverse pressure levels and the intensity of the oblique shock waves. The duct flow mild oscillations are seen for duct section 3D, 5D, 6D, and 10D. The duct length portrays a crucial role while determining the stream development in the enlarged circular tube. When the duct's size is 6D and 10D, the low wall pressure is seen. For NPR = 5, the wall pressure takes moderate values due to the influence of the tube. At NPR = 7, 9, and 11, the pressure rise is limited within the reattachment zone, and ambient conditions are nearly attained within a short duct length. Despite nozzles, they are over-expanded flow control effects in a rise of pressure at Mach 2.58 for duct size 6D and 10D. For the duct size 10D, the attainment of ambient pressure is further advanced towards the upstream.

Buzz characteristics and separation bubble dynamics in supersonic intake

The flow field in an axisymmetric supersonic mixed-compression inlet is numerically solved to understand the separation bubble dynamics at different freestream Mach numbers of M∞ = 2.0, 3.0, 5.0, and throttling ratios of ψ = 0.515, 0.40, and 0.35. The two-dimensional compressible Reynolds Averaged Navier Stokes equations were solved in a finite volume framework. The computational results were validated with the wind tunnel experimental data for steady as well as unsteady operating conditions. Throttling conditions are simulated by varying the exit area of the model in the form of plug inserts. The analysis of the flow features in the complete computation domain indicates the formation of multiple separation bubbles near the exit plug as well as near the isolator entrance of the inlet. The frequency of unsteadiness (f) associated with the ramp surface pressure decreases with a decrease in throttling ratio ψ. The possibility of a common origin that is regardless of any buzz criteria is analyzed by considering separation and reattachment zones in the flow field in terms of wall shear stress variation. Inside the supersonic intake, the multiple shock waves interact with the wall boundary layer that can lead to a large separation bubble. This bubble is always unstable inside the intake flow passage and can generate the source of instability. The propagation of a pressure disturbance is analyzed by the temporal variation of the pressure on the ramp wall. The cross-correlation coefficient Cij(t) of the pressure signal on the ramp surface suggests the upstream propagation of the disturbance generated from the separation zone near the exit plug. The numerical Schlieren provides further information on the formation and propagation of the separation bubble near the exit plug.

Mitigation of shockwave induced boundary layer separation through a secondary recirculation duct in a hypersonic flow

A secondary recirculation duct which leaks fluid from a high pressure reattachment zone to a low pressure upstream location of a shock wave boundary layer interation zone is discussed in the below article. The mitigation can be attributed to both suction and blowing. Computational analyses of the above problem at a freestream of Mach 8.6 with various jet injection locations were studied for its effectiveness via a commercial software ANSYS Fluentl9 and the results are very promising. The jet injection close to the separation point is found to be most effective in delaying separation and reducing the separation bubble.

Microclimatic Effects of a Forest-to-Peatland Transition on Aerodynamic Resistance to Water Vapour Transfer in the Sub-humid Boreal Plains

Peatlands often experience turbulent sheltering from their surrounding upland forests, which results in spatially variable surface–atmosphere exchanges of momentum, heat, and moisture produced by flow-separation dynamics, which suppresses the transport of such scalars in the sheltered region while promoting transport in the reattachment zone. With evapotranspiration being the dominant source of water loss in the Boreal Plains, it is necessary to understand the dynamics and controls on evapotranspiration within these peatlands. We used the regional atmospheric forest large-eddy simulation (RAFLES) model to study the impact of flow separation and surface roughness on microclimates leeward of a forest-to-peatland roughness transition. We parametrized our simulation with observed vegetation characteristics and meteorological data from three natural peatlands to accurately estimate natural ranges of peatland roughnesses and energy dynamics. Our simulations show that changes to peatland roughness do not affect the distances required for flow reattachment, and therefore the size of the sheltered region. However, increasing the surface roughness produces greater surface turbulence, quicker flow recovery, and decreased flow reversals within the sheltered region. Further, substantial microclimatic differences are observed throughout the flow regions of the roughness transition. Our results show that turbulence, aerodynamic resistance, and the microclimate vary throughout the backward-facing step transition and should be taken into account when estimating the spatial dynamics of evaporative demand leeward of a roughness transition. Furthermore, increasing the surface roughness of a peatland minimizes the spatial variability of turbulent drivers of evapotranspiration across a roughness transition. That is, flow separation and the surface roughness of the peatland should be accounted for when estimating the spatial variability and total evaporative potential across a peatland.

Study on Flow Characteristics of Three-Dimensional Backward-Facing Step at High Reynolds

Fan, J.; Yan, C.; Lei, P.; Wang, C., and Liu, G., 2020. Study on flow characteristics of three-dimensional backward-facing step at high Reynolds. In: Gong, D.; Zhang, M., and Liu, R. (eds.), Advances in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 106, pp. 522–525. Coconut Creek (Florida), ISSN 0749-0208.Based on FLUENT, the three-dimensional Realizable k-e turbulence model is used to simulate the flow over a backward-facing step at 40 Reynolds numbers between 500 and 80,000, and the results are combined with the results of particle image velocimetry experiments to verify the reliability of the model. The three-dimensional flow characteristics of the flow over a backward-facing step at Re = 25,822 are analyzed. The results show that in the two-dimensional aspect, the numerical simulation results are in good agreement with the experimental values, the separation and reattachment zone length change curves are consistent, the flow field structure is similar, and the model reliability is high. In three dimensions, slight differences occur in the flow distribution of the sections perpendicular to Z axis, and the closer the section is to the wall, the greater the change of flow is. Along the Z axis, the velocity and turbulent energy of water flow are unevenly distributed in the spreading direction, showing strong three-dimensional flow characteristics.

Experimental Study on Unsteady Characteristics of Shock and Turbulent Boundary Layer Interactions

In this paper, the experimental study on the shock wave and turbulent boundary layer interactions was performed in the Mach 3.4 supersonic low-noise wind tunnel. The angle of the shock generator was θ = 15°, and the unit Reynolds number of 6.30 × 106 m–1. The wall temperature and pressure distribution during the disturbance process of the shock wave and the turbulent boundary layer were obtained based on the temperature-sensitive paints technique and the flush air data sensing system, and the basic flow field of the interactions region was partitioned. Meanwhile, based on the nano-tracer planar laser scattering technique, and the instantaneous fine structures in the interaction region were obtained and the spatiotemporal evolution characteristics of the flow structure were analyzed. The flow visualization images showed that the oscillation position of the induced shock wave satisfied the normal distribution. Compared with the flow visualization images and the temperature results, the correlation between the flow structure of the interactions region and the wall temperature change was obtained. At the same time, the wall fluctuation pressure of the center surface of the shock wave and turbulent boundary layer interactions region was measured by the high-frequency pulsating pressure sensor. The power spectrum density results showed that under the action of the shock wave incident by the shock generator, there were two characteristics frequency signal of 12 and 30 kHz in the induced shock oscillation interval. For the signal of 12 kHz, the frequency value and the amplitude were increased from the turbulent boundary layer to the separation bubble, and the oscillation energy of the induced shock wave was enhanced. The amplitude of the peak signal of each measurement point gradually decreased from the separation bubble to the reattachment zone, and the energy was gradually attenuated. For the high frequency signal of 30 kHz, the frequency variation of each channel was relatively small, relatively stable, and the energy was concentrated.