Total Pressure Recovery Research Articles

Experimental and numerical investigation on a supersonic inlet with large bleed window

AbstractThe design of a two-dimensional supersonic inlet with large bleed window at low Mach number was developed. Numerical simulation and wind tunnel experiments were carried out to investigate the aerodynamic performance and variable geometric rules of the inlet. The result indicates that the single-degree-of-freedom variable geometry scheme adopted in this paper guarantees the steady work of the inlet over a wide speed range. The large bleed window caused by rotation of the compression ramp appears near the throat at low Mach number. Low-pressure airflow near the bleed window neutralises the original high-pressure airflow behind the shock train, which decreases the overall pressure of the downstream region of the internal contraction section. To match the lower pressure, the structure of the shock train changes from strong $\lambda$-type to weak $\lambda$-type, and finally to a normal shock wave as backpressure increases at Mach number 2.5. Herein, the total pressure recovery coefficient of the inlet near the critical condition improves by 8.5% as the backpressure ratio (Pe/P0) adds from 13 to 14.6 at Mach number 2.5. It proves that the scheme is effective on terminal shock wave control and inlet performance improvement. In addition, due to the background wave and the bleed window, two kinds of shock wave oscillation occur when the backpressure ratio is 13.1.

Direct-Connect Test of Solid Scramjet with Symmetrical Structure

The solid scramjet has become one of the most promising engine types. In this paper, we report the first direct-connect test of a solid scramjet with symmetrical structure, carried out using boron-based fuel-rich solid propellant as fuel. During the test, which simulated a flight environment at Mach 5.6 and 25 km, the performance of the solid scramjet was obtained by measuring the pressure, thrust, and mass flow. The results show that, due to the change in the combustion area of the propellant and the deposition of the throat in the gas generator during the test, the equivalence ratio gradually increased from 0.54 to 0.63. In a solid scramjet, it is possible to obtain a symmetrical distribution of the flow field within the combustor. Moreover, in a multi-cavity combustor, the combustion state expands from the cavity to the center of the flow channel. The performance of the solid scramjet increased during the test, reaching a combustion efficiency of about 42%, a total pressure recovery coefficient of 0.35, and a thrust gain specific impulse of about 418 s. The solid scramjet with symmetrical structure is feasible. The cavity configuration adopted in this paper can reduce the ignition delay time of fuel-rich gas and improve the combustion efficiency of gas-phase combustible components. The shock trains in the isolator are conducive to the recovery of the total pressure. The performance of the solid scramjet is limited by the low combustion efficiency of the particles.

Optimization of the aerodynamic characteristics of a NACA air intake based on DoE and numerical methods

The Design of Experiment (DoE) method combined with numerical simulations is employed to optimize the aerodynamic characteristics of a National Advisory Committee for Aeronautics (NACA) air intake. The drag force, total pressure recovery coefficient, mass flow rate at the outlet, and Mach number at the outlet are used to evaluate the performance of the air intake based on computational fluid dynamics (CFD) numerical methods. Three critical geometric parameters, namely the ramp angle a, ramp divergence angle θ, and turning corner radius R, are considered as variables in the DoE design. Results under the baseline conditions indicated that axial vortexes are formed near the side edge close to the ramp wall. DoE analysis indicated that above four performance parameters are largely influenced by the ramp angle a, while the ramp divergence angle θ has negligible effects. A small radius of the turning corner is beneficial to enhance the pressure recovery coefficient and the mass flow rate. The Mach number at the outlet declines and the velocity uniformity on a certain section increases with decreasing value of ramp angle a. Meanwhile, larger total pressure recovery coefficient, mass flow rate, and vortex tube length are acquired under a smaller value of a. Thus, the aerodynamic performance of this air intake can be improved by a set of optimized geometric parameters.

Обґрунтування моделі турбулентної в’язкості для дослідження характеристик співвісного гвинтовентилятора і вхідного пристрою ГТД

The issues of substantiation of the most rational, based on adequacy, model of turbulent viscosity for mathematical modeling of the flow near the propfan and in the inlet of the turbine-propeller engine are considered. It was found that at present there is no universal turbulence model for determining the parameters of the boundary layer, energy loss in the flow, and laminar-turbulent transition. Analysis of the results of previous studies showed that there is a need to select and justify a turbulent viscosity model for each type of research object. The task of modeling the flow near the propfan and in the inlet device of the power plant was performed using the ANSYS CFX software product, which allows using various standard mathematical models and tools for modeling turbulent flow. The object of research is an annular axial inlet device, in front of which there is a coaxial propfan with two rows of propellers: the first row has eight blades, the second - six. 7 types of models of turbulent viscosity, which most fully describe the phenomena in the flow around the propfan and the inlet device, have been investigated: k-ωmodel; SSТ (shear stress transport) SST Transitional №1 Fully turbulence; SST Transitional №2 Specified Intermittency; SST Transitional №3 Gamma model; SST Transitional №4 Gamma theta model; SST Transitional №5 Intermittency. The results of mathematical modeling of the flow near the propfan and in the inlet device at the corresponding operating mode of the turbopropfan engine using the selected models of turbulent viscosity, the total pressure value in front of and behind the inlet device was obtained to determine the total pressure recovery coefficient in it and the value of the propfan thrust. The value of the recovery factor of the total pressure in the inlet device and the propfan thrust are compared with the flight test data of the prototype. An analysis of the comparison of the values of the total pressure recovery factor in the inlet device and the propfan thrust showed that the use of the SST Transitional №4 Gamma theta model allows obtaining the value of the total pressure recovery factor in the inlet device and the propfan thrust that is closest to the flight test results.

Design and analysis of a supersonic axisymmetric inlet based on controllable bleed slots

Aiming at the problem of starting and inlet-engine matching of axisymmetric variable geometry inlet with complex structure, a novel design concept of axisymmetric inlet is proposed based on controllable bleed slots switch. The laws of the typical geometric parameters of multi-slots effecting on inlet start, supercritical and subcritical performances are numerically studied. Accordingly, a three-dimensional aerodynamic design scheme of the inlet operating at Ma1.5-4 and control laws of the bleed slots are gained, which is slightly altered inlet surface and structure is simplified. The aims of minimum starting Mach number to 2 and inlet-engine matching inlet are achieved by controlling switch of bleeding slots, and inlet operates well at high total pressure recovery and low exit Mach number. The results show that: at Ma=2, the inlet starts with 30% bleeding and 16.5% total pressure recovery coefficient improving; At Ma=3, mass flow of inlet-engine matches with 23% subsonic bleeding but cost of total pressure loss about 2.6%.

Design and validation of a two-dimensional variable geometry inlet

Abstract The design of a two-dimensional variable geometry inlet which applied to a tandem type turbine-based combined cycle (TBCC) propulsion system was investigated in the present paper through three-dimensional simulations and wind tunnel tests. The operation Mach number range was between 0 and 3. A multi-ramp geometry scheme was adopted to achieve acceptable performance at different inflow Mach number. The first ramp angle was fixed whilst the angles of the second and the third ramps were variable at different inflow Mach numbers. The Mach numbers at throat region were maintained between 1.3 and 1.5 at different inflow Mach numbers according to this variable geometry scheme. A fixed geometry rectangular-to-circular shape diffuser was adopted to improve aerodynamic performance of the inlet. Three-dimensional numerical simulations were carried out between Ma1.5 and Ma3.0. The results indicated that good aerodynamic performance can be achieved at different inflow speed. At the design point, total pressure recovery of the inlet was 0.66 at critical condition. Wind tunnel validation experiment tests were conducted at Ma2.0, showing the movement of terminal shock wave from downstream to upstream as the back pressure increased. The inlet operated at supercritical, critical and subsonic conditions at different back pressure.

Effect of turbulence model uncertainty on scramjet strut injector flow field analysis

The effect of turbulence model closure coefficient uncertainty on the Reynolds-averaged Navier–Stokes solution of a scramjet strut fuel injector flow field is investigated with an uncertainty quantification and sensitivity analysis study for the Menter-BSL and Wilcox-2006 k-ω turbulence models. Simulations were performed using the VULCAN flow solver. Nonintrusive polynomial chaos theory was used for efficient propagation of uncertainty, and Sobol indices were utilized to quantify the sensitivity of various solution metrics to the variation of each closure coefficient. The output metrics of interest were evaluated at three crossflow planes, and included the integrated quantities of mixing efficiency, circulation, total pressure recovery, and one-dimensional Mach number, as well as the pointwise vorticity and eddy viscosity distributions. Influential sets of closure coefficients were identified for each turbulence model, with the Kármán and diffusion constants being the most prominent. These results are expected to assist future efforts aimed at reducing the uncertainty in the numerical design of scramjet fuel injectors through the identification of closure coefficients and physical aspects of the flow that warrant further investigation.

Design and evaluation of a conical hypersonic vehicle with an overturned aerodynamic layout

A conical hypersonic vehicle with an overturned aerodynamic layout was accomplished and its aerodynamic performances were evaluated. In this work, the aerodynamic design methodology was addressed firstly, and then the conical vehicle integrated with an overturned inlet was obtained. The mass flow capture performance and the total pressure recovery performance were evaluated under design and off-design conditions. Results show that the mass flow capture increases and the total pressure recovery decreases as the inflow Mach number increases. The total pressure recovery decreases when the inflow Mach number increases. After that, the self-starting performance of the inlet was obtained by simulating an accelerating process. The initial inlet self-starts at Mach 5.2 on attack angle 6∘ situation. Furthermore, an improvement of the inlet self-starting performance was achieved with keeping the designed mass flow capture almost constant. By altering the 3-D shape of the inlet leading edge, the inlet self-starting Mach number decreases from Mach 5.2 to Mach 4.6 on attack angle 6∘ situation.

Shock dynamics and expansion characteristics of an aerospike nozzle and its interaction with the rotating detonation combustor

The flow of products through the aft-end of a detonation combustor is intrinsically unsteady, ultimately resulting in periodic and nonuniform flow parameters at the exit plane of a rotating detonation combustor. Therefore, the integrated design of the nozzle and combustion chamber is an important challenge in rotating detonation engines (RDEs). This paper describes a thorough three-dimensional numerical simulation of a hydrogen–air rotating detonation combustor with/without an aerospike nozzle and investigates the nozzle flow without a combustor. The simulation results allow us to analyze the coupling characteristics of the rotating detonation combustor and the aerospike nozzle. The new features of the shock wave dynamics and expansion characteristics in the nozzle with/without an integrated RDE combustor are compared. For the same rotating detonation combustor exit, the propagation mode of the detonation wave and backpressure in the RDE combustor exit are affected by the aerospike nozzle. The intensity of the shock wave and the angle with respect to the direction of the air flow are lower with the aerospike nozzle than in the nozzleless model, which is consistent with the effect of backpressure increase on the shock dynamics. Regardless of whether the nozzle is connected to the combustor, the nozzle affects the dynamic alternation of the design point state to over-expansion and under-expansion along the circumferential direction. The shock wave intensity and total pressure recovery inside the nozzle with the combustor are slightly stronger than those in the nozzle without the combustor. Consequently, the thrust and total pressure recovery of the nozzle integrated with the RDE combustor are enhanced by 7% and 5.6%, respectively. Thus, decoupling the nozzle from the rotating detonation combustor is feasible for testing the design performance of the unsteady nozzle.

Multipoint Design Optimization of Busemann-Based Intakes for Scramjet-Powered Ascent Flight

Scramjet engines are one of the most promising hypersonic airbreathing propulsion technologies for robust, efficient, and economical access to space. Multi-objective design optimization has been conducted for Busemann-based intakes in inviscid and viscous regimes at single and multiple design points, respectively, by means of surrogate-assisted evolutionary algorithms coupled with computational fluid dynamics in the present research. Intake geometries are generated by applying geometric alterations to the full Busemann intake via leading-edge truncation, axial stunting, and radial contraction, aiming to simultaneously minimize intake drag and maximize the compression efficiency at two different design conditions (i.e., Mach 7.7 at an altitude of 30 km and Mach 10 at 33.5 km on a constant dynamic pressure ascent trajectory). The single-point inviscid optimization study has found that the nondominated solutions obtained from minimizing drag and maximizing compression efficiency are approximately the same as those obtained from maximizing total pressure recovery and minimizing static pressure ratio. From the multipoint viscous optimization study, the optimal solutions have been found to retain the original advantages of the inviscid full Busemann intakes in terms of high compression efficiency with shorter intakes and higher static pressure as well as adequately high mean exit temperature for both design conditions.

A low-loss vector exhaust guide vanes and its application

The exhaust device of gas-driven fan propulsion system (for a VTOL aircraft) adopts vector exhaust guide vane (VEGV) to achieve vector thrust in the range of 0-90°, which requires that the deflection angle of the VEGV reach about ±45∘ and the total pressure recovery coefficient above 0.985. Therefore, the exhaust device needs a wide-range and low-loss VEGV to ensure efficient operation of the propulsion system. And the key of this VEGV is to eliminate the separation of the suction side under large deflection angle. So, this paper designed a new type of VEGV that can meet the demands by reducing the inverse pressure gradient of the suction surface (one of the necessary conditions for two-dimensional separation). In order to realize this design process, the spectral method of small disturbance equation (SMSDE) for two-dimensional subsonic flow was developed. Then, two VEGVs were designed by the SMSDE and verified by numerical simulation with Reynolds number 106 and blade solidity 1.18. The results show that the two VEGVs eliminate the separation of suction side at inlet Mach number of 0.25 and blade stagger angle of 45°. And the VEGV with lateral blade guarantees this characteristic up to Mach 0.3. Besides, when the inlet Mach number is below 0.3, the VEGV with lateral blade can ensure that the total pressure recovery coefficient is greater than 0.985, the outlet area ratio is greater than 0.95 and the exhaust angle error is less than 3.5°. Finally, Experimental verification of the vector exhaust device using the VEGV with lateral blade was carried out. The results show that the new VEGV has a higher total pressure recovery coefficient and outlet area ratio than the traditional VIGV at large deflection angles.

Numerical Investigation of the Inlet with Different Lip-plane Shapes under Ground Running

The inlet of the UAV is usually designed on the back of the aircraft in order to give consideration to the overall arrangement and stealth performance. Under ground running, there are often severe vortices in the duct of the backpack inlet, which leads to low total pressure recovery and large circumferential distortion index at the AIP. Different shapes of the lip-plane produce different vortices, which have great impact on circumferential distortion index at the AIP. In this paper, the characteristics of three different lip-plane shapes were studied under the ground running. Results indicate: (1) W-shaped inlet has lowest circumferential distortion index and the flow distribution is the most uniform at the AIP; (2) Λ-shaped inlet has the weakest of the vortex strength and the largest total pressure recovery, which means the thrust loss caused by the inlet is smallest; (3) V-shaped inlet has the strongest vortex strength and the lowest total pressure recovery.

Optimization Design and Experimental Study of S-shaped Inlet

Lip and diffuser are two important parts of S-shaped inlet, which are difficult to balance in the optimization design of S-shaped inlet. This paper presents an optimization method for S-shaped inlet. Firstly, the parametric models of the lip and the diffuser are established. Combining with automatic mesh generation technology, numerical simulation and genetic algorithm, an optimization platform of s-shaped inlet design based on Isight is established. Aiming at the design of inlet for an unmanned aerial vehicle (UAV), compared with the prototype, the total pressure recovery coefficient of the optimized inlet obtained by this optimization method is increased by 1.5%, and the steady-state circumferential distortion is reduced by 58.6%. The wind tunnel experiment is carried out to obtain the aerodynamic performance of the inlet, and the experimental results are in good agreement with the numerical simulation results.

Performance of 2-D inlets with curved compression surface formed by segments with controllable compression angle

Suppose that curved surface consists of tiny polylines. Two 2-D inlets with curved surfaces formed by equal compression angles of the micro-element segments and a slight increase in the compression angle of the micro-element segments are designed respectively. The numerical simulation method is used to compare the performance of two curved surface 2-D inlets with the reference three-wedge compression 2-D inlet. Select NASA classic test data, in order to determine the turbulence model and calculation method chosen by the numerical simulation Fluent software. Numerical simulation results show: the pressure ratio of the curved compression system at the place corresponding to the wedge compression second shock wave is only 0.55 of the wedge compression pressure ratio, which is much smaller than the critical pressure ratio of the boundary layer separation; at design point, the performance of three inlets is similar; at non-design points, the 2-D inlets with the curved surface have a higher flow coefficient and total pressure recovery coefficient. The configuration of the small segments compression angles is the key to the performance of the curved surface compression two-dimensional inlet.

Parameterization and optimization design of a two-dimensional axisymmetric hypersonic inlet

Optimization method, as a promising way to improve inlet aerodynamic performance, has received increasing attention. The present research is undertaken to design a two-dimensional axisymmetric hypersonic inlet using parametric optimization. The inlet configuration is parameterized and optimized in consideration of total pressure recovery and starting performance. A Pareto front is obtained by solving the multi-objective optimization problem. Then, the flow structures of the optimized inlets are analyzed and the starting performances are evaluated. Results show that the total pressure loss mainly occurs in the internal contraction section, especially near the inlet entrance, and therefore the total pressure recovery coefficient can be greatly improved by decreasing external compression. As a result, the guidance for designing high-performance inlets is concluded. Besides, it is found that as the internal contraction ratio increases, the inlet starting ability becomes worse, which attributes to the larger separation bubble at the inlet entrance. Finally, the total pressure recovery coefficient and the starting Mach number of the optimized inlets are obtained, which can be a reference for engineering design.

Design and aerodynamic performance analysis of a variable geometry axisymmetric inlet for TBCC

Abstract Design and aerodynamic performance analysis of a variable geometry axisymmetric inlet was carried out for tandem scheme turbine-based combined cycle (TBCC) propulsion system. The operation Mach number of the inlet was between 0 and 4. The design point was chosen as Mach number 4.0 in this paper. The determination of external and internal compression and the design method of annular to circle diffuser were illustrated. The inlet was unstart under Ma 3.0 without adjustment. Then, a variable scheme was designed to ensure self-start of the inlet and match the requirement of mass flow rate during the whole flight envelope. And four supports were used to fix the spike. According to the 3D numerical simulations, the total pressure recovery was 0.52 at Ma 4.0 at critical condition and the mass flow rate was consistent with the requirement at different flight Mach number.

Performance evaluation for scramjet based on ground direct-connected test: A method investigation

Scramjet has become one of the most efficient hypersonic vehicles because of its broad application potentiality. The ground direct-connected test is a relatively easy and economical way to test the performance of the scramjet under “real” condition. In this paper, an efficient performance evaluation method based on ground direct-connected test was developed. It can determine the performance parameters of the scramjet combustor (internal resistance, combustion efficiency, and total pressure recovery coefficient) and that (specific impulse and thrust) of the overall scramjet during the working time under the assumptions of adiabatic inlet and adiabatic-isentropic nozzle. Compared with the previous evaluation methods, using this method not only greatly reduces the time and money cost, but also provides more accurate boundary conditions for unsteady numerical simulation, and reference values for free jet and flight test furtherly. In the end, a case analysis was conducted and the real-time performance parameters were obtained. The results show that the internal resistance, combustion efficiency, and total pressure recovery of combustor are about 280 N, 0.69, and 0.21, respectively. The specific impulse and thrust of the overall scramjet reach about 6000 Nskg−1 and 370 Nskg−1, correspondingly.

Numerical analysis on the conceptual design of an air-breathing engine inlet working in mach number 3∼5.5

Based on the equal-intensity shock theory, this article designed a supersonic inlet working in Mach number 3.0∼5.5 with the background of an air-breathing engine. The inlet applied the four-shock train mixed compression configuration and inserted a sidewall compression at the beginning of the isolator. Through developing effective 3D RANS computations validated by current experiments, the performance of the designed inlet was identified. The designed inlet self-starts at freestream Mach number Ma∞ = 3.0 under which the total pressure recovery coefficient has dramatic increment, and the aerodynamic choking at the inlet throat no longer presents; the inlet keeps working at all studied flight states with zero angle of attack (AoA) and achieves shock-on-lip at the design point Ma∞ = 5.0. Both positive and negative AoAs can disrupt the equal-intensity shock allocations, which degrade the inlet performance. The inlet obtains maximum total pressure recovery coefficient at zero AoA. The maximum back pressure at Ma∞ = 3.0∼5.5 obtained by the inlet surpasses the requirements and keeps a certain margin. The inlet performance basically meets all the goals proposed by the engine.

Design space optimisation of an unmanned aerial vehicle submerged inlet through the formulation of a data-fusion-based hybrid model

ABSTRACTThe research focuses on the design space optimisation of National Advisory Committee for Aeronautics (NACA) submerged inlets through the formulation of a hybrid data fusion methodology. Submerged inlets have drawn considerable attention owing to their potential for good on-design performance, for example during cruise flight conditions. However, complexities due to the geometrical topology and interactions among various design variables remain a challenge. This research enhances the current design knowledge of submerged inlets through the utilisation of data mining and Computational Fluid Dynamics (CFD) methodologies, focusing on design space optimisation. A two-pronged approach is employed where the first step encompasses a low-fidelity model through data mining and surrogate modelling to predict and optimise the design parameters, while the second step uses the Design of Experiments (DOE) approach based on the CFD results for the candidate design geometry to construct a surrogate model with high fidelity for design refinement. The feasibility of the proposed methodology is demonstrated for the optimisation of the total pressure recovery of a NACA submerged inlet for the subsonic flight regime. The proposed methodology is found to provide good agreement between the surrogate and CFD-based model and reduce the optimisation processing time by half in comparison with conventional (global-based) CFD optimisation approaches.

Study on the aerodynamic performance of boundary-layer-ingesting inlet with various geometries

The mixing loss in S-shaped duct causes the contradiction between the total pressure recovery and circumferential distortion, which confuses the design process for boundary layer ingestion (BLI) inlet. This article is aiming to present a detailed understanding of the effect of two kinds of loss resources (mixing loss and frictional loss) on the performance for various BLI inlet geometries. To achieve the above objective, a design method including three control parameters is established. With this method, a systematic investigation of control parameters on the performance of BLI inlet is carried out, which leads to the contour map for the performance of BLI inlet. Based on the map, the flow physics of BLI inlet with two kinds of losses is then analyzed. Finally, an empirical design principle is provided. The results show that the appropriate design for BLI inlet has the potential to increase the total pressure recovery or reduce the circumferential distortion.