COMPARISON OF PERFORMANCE OF CONIC AND RAMP INLET USING CFD

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 7, July 2017, pp , Article ID: IJMET_08_07_023 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed COMPARISON OF PERFORMANCE OF CONIC AND RAMP INLET USING CFD Alekhya. N Assistant Professor, Department of Aeronautical Engineering MLR Institute of Technology, Hyderabad, Telangana, India N. Prabhu Kishore Associate Professor, Department of Mechanical Engineering MLR Institute of Technology, Hyderabad, Telangana, India M. Satyanarayana Gupta Professor, HoD, Department of Aeronautical Engineering MLR Institute of Technology, Hyderabad, Telangana, India Y. Swetha Assistant Professor, Department of Aeronautical Engineering Institute of Aeronautical Engineering M Vishnu Vardhan Department of Mechanical Engineering Vardhaman College of Engineering, Hyderabad, Telangana, India ABSTRACT An aircraft travelling at the supersonic speeds undergoes a vibration called as shock waves. These shock waves are caused as an airplane reaches the speed of sound, the air ahead of it receives no warning of the plane s approach. So the airplane moves faster through the air which indeed produces the shockwaves. When the aircraft experiencing the shock wave, its pressure, density, and temperature all increase abruptly. If these shockwaves enters into the engine causes damages in the blades and even can lead to the failure of the engine. So the in order to control these shock waves use of supersonic inlets came into existence. In this paper, two types of supersonic inlets are analyzed and compared for their better performance. The conic and ramp inlets are the main inlets used mostly for all the supersonic aircrafts. The total pressure recovery is the main parameter to judge between the inlets. More the pressure recovery index, better the performance. Key words: Supersonic, Inlet, Conic Inlet, Ramp Inlet, Shock Waves editor@iaeme.com

2 Alekhya. N, N. Prabhu Kishore,M. Satyanarayana Gupta, Y. Swetha and M Vishnu Vardhan Cite this Article: Alekhya. N, N. Prabhu Kishore,M. Satyanarayana Gupta, Y. Swetha and M Vishnu Vardhan, Comparison of Performance of Conic and Ramp Inlet Using CFD. International Journal of Mechanical Engineering and Technology, 8(7), 2017, pp INTRODUCTION An inlet for a supersonic aircraft has a sharp lip which is used to minimize the performance losses from shock waves [7]. For a supersonic aircraft, the inlet must slow the flow down to subsonic speeds before the air reaches the compressor. Some supersonic inlets like conic inlets use a central cone to cut down the flow to subsonic speeds. Normally in shockwaves, the properties of the fluid surrounding the aircraft change very abruptly which result in the vibrations of the body. There are two types of shockwaves namely: normal shock wave, oblique shock waves [1]. These are the types which are mostly experienced by the pilots in supersonic aircrafts. At the region where this occurs, sound waves travelling against the flow reach a point where they cannot travel any further upstream and the pressure progressively builds in that region; a high pressure shock wave rapidly forms Conic Inlets The conic inlet is mainly used to slow down the flow of the supersonic air to subsonic air before entering the engine. All the air breathing engines except scramjets, requires such kind of inlets to reduce the speed of the air entering [2]. This conic inlet sloping rearwards, forms the apex of the cone with which air passes through a strong normal shock wave within the diffuser passage and then enters inside with subsonic velocity. A sharp-lipped version of the pitot intake, described above for subsonic applications, performs quite well at moderate supersonic flight speeds. A detached normal shock wave forms just ahead of the intake lip and 'shocks' the flow down to a subsonic velocity. Although centre-body diffusers and intakes are more describes at high supersonic Mach numbers than a pitot-type intakes on account of the improvement in pressure recovery, they are often prone to violent prone to violent flows oscillations for part or all of the mass flow oscillations is complex but two main types can be recognized. One we shall call the larger oscillation and the other the small or organ pipe oscillations. As the mass flow through the diffuser is reduced, the flow configuration at the entry has to adjust itself to satisfy the new requirement. Fig below shows such a configuration with air being spilled round the outside of the cowl with a three-shock configuration ahead of the diffuser. Figure 1 Centre-body diffuser Full mass flow editor@iaeme.com

3 Comparison of Performance of Conic and Ramp Inlet Using CFD 1.2. Ramp Inlets The ramp inlet is one of the type of the supersonic inlets which is rectangular in shape and is designed to generate a number of shock waves to aid the inlet compression process at supersonic speeds. The deflection of the air stream creates a number of oblique shock waves at each change of gradient along at the ramp. It avoids the air spillage and pre occurrence of drag on the body. The advanced supersonic inlets includes ramp with number of changes to generate the multiple oblique shock waves. The inlet ramp is followed by a diverging ramp which makes the air to pass through the first ramp to become the subsonic and the second ramp reduces the air stream velocity and then increases the pressure. This inlet is known for the best pressure recovery and also improves the fuel efficiency. Figure 2 Figure showing the working of ramp inlet The preliminary design for a two dimensional mixed compression, two ramp supersonic inlets to maximize total pressure recovery and match the mass flow demand of the engine. For an on-design condition, the total pressure recovery is maximized according to the optimization criterion, and the dimensions of the inlet in terms of ratios to the engine face diameter are calculated. The optimization criterion is defined such that in a system of (n-1) oblique shocks and one normal shock in two dimensions, the maximum shock pressure recovery is obtained when the shocks are of equal strength. This paper also provides a method to estimate the total pressure recovery for an off-design condition for the specified inlet configuration. The variable ramp provides the air to be smoothened and optimized as it can. So the ramps are given the stages in the inlet which dissolves the shockwave and gives a smooth air flow inside the compressor to increase the pressure. The aerodynamic design of a supersonic intake becomes a critical issue to estimate the overall performance of an air-breathing propulsion system which operates at supersonic to hypersonic speeds and captures the incoming air to supply to combustor of main engine after compression. 2. OPTIMIZATION CRITERION TO MAXIMIZE THE PRESSURE RECOVERY In order to maximize the pressure recovery index for any inlet, optimization of the angles and the supersonic sections are to be done. The optimization criterion is mainly used for the determining the ramp angles in the supersonic section. The optimization is the iterative process by which the accurate results can be obtained and also is the faster way. As the important parameter in the supersonic inlets or subsonic inlets is pressure recovery index which is pressure gained by the fluid while shock wave and after shock wave. So the maximum the pressure recovery is the better performance of the inlet will be. So to get the maximum shock pressure recovery the shock waves of equal strengths are considered. That is the mach numbers perpendicular to the individual shocks are equal as shown in the equation 1. M 1sin 1 = 2 = 1 1 (1) editor@iaeme.com

4 Alekhya. N, N. Prabhu Kishore,M. Satyanarayana Gupta, Y. Swetha and M Vishnu Vardhan Figure 3 Multi Shock Compression For Optimization Assume the on-design cruise speed is the highest speed the aircraft will fly. Then at offdesign points, in general, the total pressure recovery will be higher than those of the on-design points because the flow speed is lower and thus the shocks are weaker and losses are less. However, it is very hard to calculate the total pressure recovery at off-design points because the flow field is much more complicated. For example, a detached shock may occur. In order to provide an estimation of inlet pressure recovery for engine performance evaluation, a conservative value of inlet pressure recovery can be given by using the following assumptions or simplifications. 1. Whenever an oblique shock becomes detached, the equations of normal shock are used to calculate the parameters of this shock, and the shock line is perpendicular to the upstream flow and the downstream flow is parallel to the ramp. 2. If the shock that originates at the lower cowl lip is an attached oblique shock, assume a normal shock will occur just after this oblique shock. The total pressure ratio of the subsonic diffuser is pr =0.98, which is a conservative estimation according to calculations performed.however, let pr=0.985 if there is detached shock because the equations of normal shock were used to calculate the parameters of this shock, resulting in resulting in lower total pressure recovery. Therefore, pr was increased a small to compensate. 3. CFD ANALYSIS The present work is a wind tunnel modeling in ICEM CFD. A rectangular domain is made and is chosen as the boundary for the inlet. This is used to stimulate on time conditions at supersonic flow regimes. In ICEM CFD the geometry model is done and is meshed. Then the model is checked to ensure connectivity of adjacent members /elements in assemblage. The model of mesh chosen is tetrahedron type, as the model is uniform in its shape. The meshed geometry is imported to CFX-pre and the conditions like temperature, pressure and velocity conditions are given to the meshed geometry model. Then it is simulated in CFXpost to obtain results. 4. RESULTS AND ANALYSIS 4.1. Cone Inlet The cone inlet is designed and a boundary is formed around it to make it a boundary condition. The modeled cone inlet is shown in the figure 4. It is then analyzed in the CFD ANSYS giving the air as the medium with Mach number editor@iaeme.com

5 Comparison of Performance of Conic and Ramp Inlet Using CFD Figure 4 Cone inlet in the boundary The pressure contours are been considered and at those contours the pressure points are considered. The total pressure is calculated with those pressure contours. Figure 5 and 6 shows the total pressure at contour 1 and Mach contour1. Figure 5 Cone inlet total pressure contour editor@iaeme.com

6 Alekhya. N, N. Prabhu Kishore,M. Satyanarayana Gupta, Y. Swetha and M Vishnu Vardhan Figure 6 Cone inlet Mach number contour 4.2. Ramp Inlet The ramp inlet is designed and is imported in CFX-pre and then to calculate the pressure is imported to CFX-post. The figure 7 shows the ramp inlet in CFX-Pre. Figure 7 Ramp inlet CFX-PRE Same as the conic inlet the pressure contours are considered and the total pressure is calculated using these contours at the Mach number 1.7. Figures 8 and 9 shows the pressure contour 1 and the total pressure contour 1 for the ramp inlet. The values obtained by this analysis are shown in the tables. These are then calculated for total pressure recovery index. This shows which is the best inlet for the better performance editor@iaeme.com

7 Comparison of Performance of Conic and Ramp Inlet Using CFD Figure 8 Ramp inlet pressure contour Figure 9 Ramp inlet total pressure 4.3. Comparison of Cone and Ramp Inlet Pressure Recovery The total pressure recovery can be measured from the total pressure difference occurred in the CFD analysis. The table 1 and 2 shows the total pressure obtained from the analysis. Table 1 Total pressure values obtained from the analysis Pressure at entry of Difference between inlet Sl. No Pressure at inlet(atm) compressor(atm) and exit pressures(pi-pe) editor@iaeme.com

8 Alekhya. N, N. Prabhu Kishore,M. Satyanarayana Gupta, Y. Swetha and M Vishnu Vardhan Sl. No Table 2 Total Pressure values obtained for Ramp inlet Pressure at inlet(atm) Pressure at entry of compressor(atm) Difference between inlet and exit pressures(pi- Pe) To calculate the total pressure recovery index for a inlet, we consider the pressure at the inlet lip and the pressure at the exit of the inlet/diffuser. The ratio of the pressure at inlet lip to exit pressure gives the inlet pressure ratio then efficiency is calculated. The total pressure recovery index ηr depends mainly on the Mach number. If the Mach number is less than 1, the pressure recovery index is equal to 1. But for supersonic inlets the shock waves enter into the inlet so the pressure recovery index is calculated as =[.. The pressure recovery is calculated for each inlet is given in the table 3 Table 3 Total Pressure Recovery Index Sl. No Conic Inlet Ramp Inlet Pressure Recovery Index Comparison of Pressure Recovery Index conic inlet ramp inlet Figure 10 Comparison of Pressure Recovery Index 5. CONCLUSIONS The two supersonic inlets, conic and ramp are mainly used to reduce the velocity of the air entering into the engine before it enter the compressor. The shock waves formed due to the supersonic speeds are intake through these inlets and are sent to the compressor as the smooth air. The diffuser oppresses the shock waves so that the engine damage is not done. The analysis of the inlets is done based on the pressure recovery index. As discussed in the results, the ramp inlet has the best total pressure recovery index. So the ramp inlet is mostly preferred for the engines operating at supersonic speeds. The conic shaped spikes are preferred to use at the nose of the aircraft as spikes to delay the shock wave formation editor@iaeme.com

9 Comparison of Performance of Conic and Ramp Inlet Using CFD REFERENCES [1] B. Alekhya, Neela Manoj Kumar. Design and Performance Analysis of Supersonic Inlets Using Computational Fluid Dynamics. IJMETMR, 3-12, 2016, pp [2] Reza Aghaei tog, Abolghasem M. Tousi, Experimental and numerical investigation of design optimization of a partial admitted supersonic turbine. Propulsion and Power Research, 7, 2013, pp [3] Chimmiri Sasanka Mouli, Chimmmiri Naga Vardhan, G Vengaiah Chowdary, Palavalli Jeevan Reddy, Aerodynamic Design and Performance of Nozzle with Different Mach Numbers Using CFD Analysis. SSRG, International Journal of Mechanical Engineering, 3, 2017, pp [4] Mayur R Anvekar. Aircraft Propulsion, Eastern Economy Edition, PHI Editions, [5] T. Narendiranath Babu, Prasanth, E. Raj Kumar, R. Mageshvaran, T. Shankar and D. Rama Prabha, Structural Analysis on Wing Box Spliced Joint for an Aircraft Using Finite Element Method. International Journal of Civil Engineering and Technology, 8(3), 2017, pp [6] Dr. Sumathy Muniamuthu, Karthikeyan T, Poovazhagan V, Poovarasan D, Ramki P, Review On one Manned Aircraft, International Journal of Mechanical Engineering and Technology, 8(3), 2017, pp [7] Yasushi Watanabe, Akira Murakami Control of Supersonic Inlet With Variable Ramp, International Congress Of The Aeronautical Science, [8] NASA inlets, editor@iaeme.com