Flow interaction between external flow and cell jet flows of a simplified clustered linear aerospike model was experimentally investigated based on the surface pressure measurements and a flow visualization using background oriented Schlieren (BOS) technique. The test model has four clustered cell nozzles with a designed Mach number of 3.47 and is connected to a straight section following a 12-degree-inclined straight ramp. It is set up in a Mach 2.0 supersonic wind tunnel to simulate conditions of supersonic external flow impinging on the cell nozzle jets and ramp surface. Under conditions with or without external flow, pressure distributions on the ramp surface were measured and compared to flow visualization results. Results of measured pressure distributions on the test model surface for the with-external flow case were obviously different due to the external flow: ramp surface pressures were maintained at a certain level above the environmental pressure level according to the cell jet expansion conditions, and the pressure distribution for conditions without-external flow can be nearly approximated by the method of characteristics. Furthermore, the external flow makes the entire flowfield on the ramp more uniform compared to that for the conditions without-external flow by eliminating periodic compression/expansion feature of jet. Flow visualization found that those tendencies are mainly governed by the fact that the external flow controls jet expansion by pressing it against the ramp wall surface. While flowfield was investigated, BOS technique itself was assessed to have better sensitivity and accuracy for a given setup.